1) The document investigates the nuclear activity of the barred spiral galaxy NGC 1672 using X-ray data from Chandra and XMM-Newton, as well as optical data from Hubble and infrared data from Spitzer.
2) It detects 28 X-ray sources within NGC 1672, with nine being ultraluminous X-ray sources located at the ends of the galaxy's bar.
3) For the first time, it shows NGC 1672 possesses a hard nuclear X-ray source surrounded by an X-ray bright circumnuclear star-forming ring, which dominates the central X-ray emission of the galaxy. The data indicates the nuclear source is a low-luminosity active gal
1. Chandra observations of the galaxy NGC 3351 revealed X-ray emission from its circumnuclear star-forming ring that is composed of numerous point-like sources embedded in diffuse hot gas.
2. The morphology of the X-ray emission is similar to but not identical with UV and H-alpha hot spots in the ring, which can be understood if star formation occurs through intermittent starbursts around the ring with different emissions tracing later evolutionary stages.
3. X-ray emission also extends beyond the ring, which is interpreted as outflowing gas from the ring into the disk and halo of NGC 3351, providing evidence for confined outflow near the plane but less restricted outflow perpendicular to
The document summarizes a study that presents the first panoramic view of the outskirts of the Milky Way analogue galaxy NGC 891 based on ground-based imaging. The key findings are:
1) Numerous stellar overdensities and coherent substructures were detected out to distances of ~90 kpc from the center of NGC 891, including a giant stream looping around the galaxy up to ~50 kpc.
2) A previously undetected large, flat, and thick cocoon-like stellar structure was found surrounding the bulge and disk of NGC 891 out to radial distances of ~40 kpc and vertical distances of ~15 kpc.
3) The properties of the substructures suggest NGC
This document summarizes observations of the debris disk around the subgiant star κ CrB using Herschel and Keck. Herschel spatially resolved images of the debris disk, the first such images of a disk around a subgiant star. Keck radial velocity monitoring provided evidence for a second planetary companion around κ CrB. Keck adaptive optics imaging placed an upper limit on the mass of this companion. Modeling of the Herschel images showed the dust is broadly distributed but could not distinguish between a single wide belt or two narrow belts. The observations are consistent with dynamical depletion or collisional erosion clearing the inner regions of the disk.
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
X ray emission-from_strongly_asymmetric_circumstellar_material_in_the_remnant...Sérgio Sacani
This document summarizes a study of X-ray emission from circumstellar material (CSM) in the remnant of Kepler's supernova. The researchers used a statistical technique to isolate X-ray emission from CSM versus ejecta based on spectral characteristics. They found that most CSM is distributed along the bright north rim, but substantial amounts are also projected against the center, indicating a disk-like distribution of CSM from the progenitor system before the supernova. Hydrodynamic simulations support an AGB star companion as the origin of the asymmetric CSM. Quantitative analysis of magnesium emission identifies CSM and requires Kepler to have originated from a close binary system.
Off nuclear star_formation_and_obscured_activity_in_the_luminous_infrared_gal...Sérgio Sacani
The document summarizes observations of the luminous infrared galaxy NGC 2623 from multiple telescopes. Hubble Space Telescope images reveal over 100 bright star clusters in a 3.2 kpc extension south of the galaxy's nucleus, making it one of the richest concentrations of clusters observed. The clusters have ages between 1-100 Myr based on their optical colors. Archival GALEX data show the extension is very bright in far-ultraviolet but less significant at longer wavelengths. Spitzer data detect [Ne V] emission, confirming the presence of an active galactic nucleus. The off-nuclear star formation corresponds to a rate of 0.1-0.2 solar masses per year, while the bulk of the infrared
A possible carbonrich_interior_in_superearth_55_cancrieSérgio Sacani
1) The document analyzes the possibility that the interior of the super-Earth exoplanet 55 Cancri e could be carbon-rich rather than oxygen-rich.
2) Models that assume an oxygen-rich interior with iron, silicates, and a water envelope cannot fully explain 55 Cancri e's mass and radius measurements. However, a carbon-rich interior containing iron, silicon carbide, and/or carbon could explain the observations without needing a volatile envelope.
3) A carbon-rich interior for 55 Cancri e is plausible given the reported carbon-rich composition of its host star, though more data is needed on the star's elemental abundances and the planet's atmosphere.
The exceptional soft_x_ray_halo_of_the_galaxy_merger_ngc6240Sérgio Sacani
The document summarizes a recent 150-ks Chandra observation of the galaxy merger NGC 6240. Extended soft X-ray emission is detected over a 110x80 kpc region around NGC 6240. Spectral analysis finds the emission comes from hot gas with a temperature of around 7.5 million K and a total mass of about 10^10 solar masses. The gas properties suggest widespread star formation over the past 200 Myr rather than a recent nuclear starburst. The fate of the diffuse hot gas after the galaxy merger is uncertain but it may be retained and evolve into the halo of an elliptical galaxy.
1. Chandra observations of the galaxy NGC 3351 revealed X-ray emission from its circumnuclear star-forming ring that is composed of numerous point-like sources embedded in diffuse hot gas.
2. The morphology of the X-ray emission is similar to but not identical with UV and H-alpha hot spots in the ring, which can be understood if star formation occurs through intermittent starbursts around the ring with different emissions tracing later evolutionary stages.
3. X-ray emission also extends beyond the ring, which is interpreted as outflowing gas from the ring into the disk and halo of NGC 3351, providing evidence for confined outflow near the plane but less restricted outflow perpendicular to
The document summarizes a study that presents the first panoramic view of the outskirts of the Milky Way analogue galaxy NGC 891 based on ground-based imaging. The key findings are:
1) Numerous stellar overdensities and coherent substructures were detected out to distances of ~90 kpc from the center of NGC 891, including a giant stream looping around the galaxy up to ~50 kpc.
2) A previously undetected large, flat, and thick cocoon-like stellar structure was found surrounding the bulge and disk of NGC 891 out to radial distances of ~40 kpc and vertical distances of ~15 kpc.
3) The properties of the substructures suggest NGC
This document summarizes observations of the debris disk around the subgiant star κ CrB using Herschel and Keck. Herschel spatially resolved images of the debris disk, the first such images of a disk around a subgiant star. Keck radial velocity monitoring provided evidence for a second planetary companion around κ CrB. Keck adaptive optics imaging placed an upper limit on the mass of this companion. Modeling of the Herschel images showed the dust is broadly distributed but could not distinguish between a single wide belt or two narrow belts. The observations are consistent with dynamical depletion or collisional erosion clearing the inner regions of the disk.
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
X ray emission-from_strongly_asymmetric_circumstellar_material_in_the_remnant...Sérgio Sacani
This document summarizes a study of X-ray emission from circumstellar material (CSM) in the remnant of Kepler's supernova. The researchers used a statistical technique to isolate X-ray emission from CSM versus ejecta based on spectral characteristics. They found that most CSM is distributed along the bright north rim, but substantial amounts are also projected against the center, indicating a disk-like distribution of CSM from the progenitor system before the supernova. Hydrodynamic simulations support an AGB star companion as the origin of the asymmetric CSM. Quantitative analysis of magnesium emission identifies CSM and requires Kepler to have originated from a close binary system.
Off nuclear star_formation_and_obscured_activity_in_the_luminous_infrared_gal...Sérgio Sacani
The document summarizes observations of the luminous infrared galaxy NGC 2623 from multiple telescopes. Hubble Space Telescope images reveal over 100 bright star clusters in a 3.2 kpc extension south of the galaxy's nucleus, making it one of the richest concentrations of clusters observed. The clusters have ages between 1-100 Myr based on their optical colors. Archival GALEX data show the extension is very bright in far-ultraviolet but less significant at longer wavelengths. Spitzer data detect [Ne V] emission, confirming the presence of an active galactic nucleus. The off-nuclear star formation corresponds to a rate of 0.1-0.2 solar masses per year, while the bulk of the infrared
A possible carbonrich_interior_in_superearth_55_cancrieSérgio Sacani
1) The document analyzes the possibility that the interior of the super-Earth exoplanet 55 Cancri e could be carbon-rich rather than oxygen-rich.
2) Models that assume an oxygen-rich interior with iron, silicates, and a water envelope cannot fully explain 55 Cancri e's mass and radius measurements. However, a carbon-rich interior containing iron, silicon carbide, and/or carbon could explain the observations without needing a volatile envelope.
3) A carbon-rich interior for 55 Cancri e is plausible given the reported carbon-rich composition of its host star, though more data is needed on the star's elemental abundances and the planet's atmosphere.
The exceptional soft_x_ray_halo_of_the_galaxy_merger_ngc6240Sérgio Sacani
The document summarizes a recent 150-ks Chandra observation of the galaxy merger NGC 6240. Extended soft X-ray emission is detected over a 110x80 kpc region around NGC 6240. Spectral analysis finds the emission comes from hot gas with a temperature of around 7.5 million K and a total mass of about 10^10 solar masses. The gas properties suggest widespread star formation over the past 200 Myr rather than a recent nuclear starburst. The fate of the diffuse hot gas after the galaxy merger is uncertain but it may be retained and evolve into the halo of an elliptical galaxy.
Star formation history_in_the_smc_the_case_of_ngc602Sérgio Sacani
This document summarizes a study of the star formation history in the NGC 602 region of the Small Magellanic Cloud based on Hubble Space Telescope observations. Deep photometry reveals numerous pre-main sequence stars as well as young stars on the main sequence, allowing the study of star formation into recent times. New pre-main sequence stellar evolutionary tracks are presented. A stellar population synthesis code is used to derive the best estimate of the star formation history by comparing observed and synthetic color-magnitude diagrams. The star formation rate in the region has increased over the past tens of Myr, reaching 0.3-0.7×10−3 M☉ yr−1 in the last 2.5 Myr, comparable to
First detection of_molecular_gas_in_shells_in_cena_galaxySérgio Sacani
This document reports the first detection of molecular gas (CO) in the shells of the galaxy Centaurus A (Cen A), located 15 kpc from the galaxy's center. The ratio of CO to HI emission in the shells matches what is found in the galaxy's central regions, which is unexpected given typical metallicity gradients in galaxies. The detection of molecular gas in the shells provides evidence that molecular gas in galaxy mergers may be spread further from nuclear regions than previously thought. The dynamics of the gas can be understood if the interstellar medium is considered clumpy and less dissipative than assumed, allowing dense gas to orbit with stars and form shells.
The physical conditions_in_a_pre_super_star_cluster_molecular_cloud_in_the_an...Sérgio Sacani
The document summarizes a study of an extreme molecular cloud in the Antennae galaxies that has properties consistent with forming a globular cluster. ALMA observations reveal a cloud with a radius of 24 pc and mass greater than 5 million solar masses. While capable of forming a globular cluster, a lack of associated thermal radio emission indicates star formation has not yet begun to alter the environment, suggesting the cloud is in an early stage of evolution. For the cloud to be confined as observed, an external pressure over 10,000 times greater than typical interstellar pressure is required, supporting the theory that high pressures are needed to form globular clusters in extreme environments like mergers.
This document summarizes the discovery of Kepler-413b, a Neptune-sized circumbinary planet orbiting the eclipsing binary star system Kepler-413. The planet has an orbital period of approximately 66 days and an eccentric orbit with a semimajor axis of 0.355 AU. Analysis of the Kepler light curve revealed the planet's orbit is misaligned with the binary star plane by about 2.5 degrees, causing it to sometimes fail to transit one of the stars. The orbital configuration of the system places the planet interior to the habitable zone but its obliquity may undergo fluctuations on precession timescales.
Creation of cosmic structure in the complex galaxy cluster merger abell 2744Sérgio Sacani
Abell 2744 is one of the most actively merging galaxy clusters known, appearing to have "dark", "ghost", "bullet", and "stripped" substructures of around 1014 solar masses each. The cluster shows a complex phenomenology that will challenge simulations to reproduce. The authors present a detailed strong lensing, weak lensing, and X-ray analysis of Abell 2744, identifying 34 strongly lensed images around the massive Southern core and producing the most detailed mass map to date. They find evidence that the Southern core and Northwestern substructure are post-merger systems similar to the Bullet Cluster viewed from an angle, and derive a new constraint on the self-interaction cross section of dark matter particles. They
Shaping the glowing_eye_planetary_nebula_ngc6751Sérgio Sacani
This document presents a comprehensive study of the planetary nebula NGC 6751 using spectroscopic observations and imaging. It finds:
1) NGC 6751 has a thick equatorial ring fragmented into knots enclosing a central bubble, surrounded by faint envelope and bipolar lobes with filaments.
2) Kinematic data identify distinct velocities for different components: the outer halo at -15 km/s, inner halo at -31 km/s, and bipolar lobes at ±30 km/s.
3) A 3D morpho-kinematic model is constructed using the SHAPE code that closely matches the observed images and spectra, providing insight into the nebula's complex structure.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
The fornax deep_survey_with_vst_i_the_extended_and_diffuse_stellar_halo_of_ng...Sérgio Sacani
We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep
Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside
two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that
the core of the Fornax cluster is characterised by a very extended and diffuse envelope surrounding
the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (∼ 192 kpc)
from the galaxy center and down to μg ∼ 31 mag arcsec−2 in the g band. The deep photometry
allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399
and towards NGC 1387. By analyzing the integrated colors of this feature, we argue that it
could be due to the ongoing interaction between the two galaxies, where the outer envelope of
NGC 1387 on its east side is stripped away. By fitting the light profile, we found that exists a
physical break radius in the total light distribution at R = 10 arcmin (∼ 58 kpc) that sets the
transition region between the bright central galaxy and the outer exponential halo, and that the
stellar halo contributes for 60% of the total light of the galaxy (Sec. 3.5). We discuss the main
implications of this work on the build-up of the stellar halo at the center of the Fornax cluster.
By comparing with the numerical simulations of the stellar halo formation for the most massive
BCGs (i.e. 13 < logM200/M⊙ < 14), we find that the observed stellar halo mass fraction is
consistent with a halo formed through the multiple accretion of progenitors with stellar mass in
the range 108 − 1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through
a major merging event. The absence of a significant number of luminous stellar streams and
tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early
formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around
NGC 1399 is characterised by a more diffuse and well-mixed component, including the ICL.
Multi wavelenth observations and surveys of galaxy clustersJoana Santos
This document provides an overview of galaxy clusters, focusing on their baryonic components (intracluster medium and galaxies) and how they relate to the cluster's physical properties like mass. It discusses that galaxy clusters form hierarchically through gravitational collapse. The intracluster medium, which makes up most of the baryonic mass, emits X-rays and has been heated to temperatures of millions of degrees. The document reviews properties of the intracluster medium like density, temperature, metallicity, and how they can be measured from X-ray spectra. It also discusses upcoming surveys that will advance the study of galaxy clusters.
Modulations in the_radio_light_curve_of_the_typeiib_supernova_2001igSérgio Sacani
This document summarizes radio observations of the Type IIb supernova SN 2001ig made with the Australia Telescope Compact Array and Very Large Array over 700 days. The observations found periodic deviations from the standard model of radio light curves that are consistent with recurring density modulations in the circumstellar medium with a period of around 150 days. This provides evidence that the progenitor was a Wolf-Rayet star in a binary system with an eccentric 100 day orbit, causing regular build-up of circumstellar material. Such binary systems are thought to produce Type Ib/c supernovae through envelope stripping, linking these events to Type IIb supernovae.
1) Researchers have developed a new technique called mechanophotopatterning (MPP) that uses light irradiation and mechanical deformation to precisely control the topology of light-responsive elastomers, establishing a new patterning method.
2) Using MPP, a variety of surface topologies can be produced, making it potentially useful for applications. When optically thick samples are irradiated, they bow into 3D shapes with promising applications in advanced optics.
3) The intrinsic material properties of the polymers remain unchanged after deformation, allowing for diverse applications at the interface of cell biology and tissue engineering through dynamic control of mechanical feedback to cells.
1) The Fermi bubbles are giant gamma-ray emitting structures extending above and below the galactic center.
2) The bubbles may have been formed by periodic capture of stars by the supermassive black hole at the galactic center, releasing energy of around 3x10^52 ergs per capture.
3) This energy injection could produce very hot plasma, accelerating electrons that produce radio and gamma-ray emission through synchrotron radiation and inverse Compton scattering.
Relativistic collapse and explosion of rotating supermassive stars with therm...Sérgio Sacani
1) The document describes general relativistic simulations of collapsing supermassive stars with and without rotation using a numerical code called Nada.
2) The simulations include effects of gas pressure, radiation, electron-positron pairs, and thermonuclear energy from hydrogen and helium burning.
3) Objects with a mass of around 5×105 solar masses explode if non-rotating with a metallicity over 0.007, while rotation lowers the threshold to 0.001. More massive objects have a higher critical metallicity for explosion.
This document summarizes the results of a deep near-infrared survey of the Carina Nebula complex using the HAWK-I instrument on the VLT. The survey imaged an area of 0.36 square degrees down to magnitudes of J=23, H=22, and Ks=21, detecting over 600,000 infrared sources. Color-magnitude diagrams of the sources were analyzed to determine properties of the low-mass stellar population such as ages and masses. The survey found that about 3200 sources have masses above 1 solar mass, consistent with expectations from the initial mass function. It also found that about half of the young stars in Carina are in a widely distributed, non-clustered configuration. Six
Salts and radiation_products_on_the_surface_of_europaSérgio Sacani
The document summarizes new observations of Europa's surface using high-resolution spectroscopy. Key findings include:
1) Distinct spectral signatures of magnesium sulfate salts were detected, confined to the trailing hemisphere and correlated with radiation products like sulfuric acid and SO2.
2) On the leading hemisphere, many proposed sulfate salts could be ruled out, though distorted water ice bands were present.
3) The association of magnesium sulfate with radiation products suggests it is a radiation product rather than a constituent of an ocean brine.
4) Based on ocean chemistry models, the authors hypothesize magnesium was primarily in the form of MgCl2 prior to irradiation, and that NaCl and KCl are even more abundant and
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
1. The spectrum of the bright Kuiper Belt object 2005 FY9 is dominated by methane absorption features in the near-infrared region. However, the methane absorption lines are significantly broader than seen on any other solar system body, indicating unusually long optical path lengths through methane grains on 2005 FY9, estimated to be around 1 cm in size.
2. In addition to methane, the spectrum also shows clear evidence for ethane, which is expected to form from UV photolysis of methane. No evidence is found for nitrogen or carbon monoxide, both known to be present on Pluto.
3. The differences between 2005 FY9's spectrum and those of Pluto and 2003 UB313 are suggested
This document summarizes the discovery and analysis of a Type Ia supernova (SN Ia) at a redshift of 1.71, the most distant spectroscopically confirmed SN Ia at the time. The Hubble Space Telescope was used to obtain spectroscopy and photometry of the supernova. Analysis of the spectroscopy confirms it as a SN Ia with 92% confidence. The photometry is used to determine the supernova's distance, which agrees with the predictions of the ΛCDM cosmological model. This distant supernova helps improve constraints on the nature and behavior of dark energy in the early universe.
Star formation history_in_the_smc_the_case_of_ngc602Sérgio Sacani
This document summarizes a study of the star formation history in the NGC 602 region of the Small Magellanic Cloud based on Hubble Space Telescope observations. Deep photometry reveals numerous pre-main sequence stars as well as young stars on the main sequence, allowing the study of star formation into recent times. New pre-main sequence stellar evolutionary tracks are presented. A stellar population synthesis code is used to derive the best estimate of the star formation history by comparing observed and synthetic color-magnitude diagrams. The star formation rate in the region has increased over the past tens of Myr, reaching 0.3-0.7×10−3 M☉ yr−1 in the last 2.5 Myr, comparable to
First detection of_molecular_gas_in_shells_in_cena_galaxySérgio Sacani
This document reports the first detection of molecular gas (CO) in the shells of the galaxy Centaurus A (Cen A), located 15 kpc from the galaxy's center. The ratio of CO to HI emission in the shells matches what is found in the galaxy's central regions, which is unexpected given typical metallicity gradients in galaxies. The detection of molecular gas in the shells provides evidence that molecular gas in galaxy mergers may be spread further from nuclear regions than previously thought. The dynamics of the gas can be understood if the interstellar medium is considered clumpy and less dissipative than assumed, allowing dense gas to orbit with stars and form shells.
The physical conditions_in_a_pre_super_star_cluster_molecular_cloud_in_the_an...Sérgio Sacani
The document summarizes a study of an extreme molecular cloud in the Antennae galaxies that has properties consistent with forming a globular cluster. ALMA observations reveal a cloud with a radius of 24 pc and mass greater than 5 million solar masses. While capable of forming a globular cluster, a lack of associated thermal radio emission indicates star formation has not yet begun to alter the environment, suggesting the cloud is in an early stage of evolution. For the cloud to be confined as observed, an external pressure over 10,000 times greater than typical interstellar pressure is required, supporting the theory that high pressures are needed to form globular clusters in extreme environments like mergers.
This document summarizes the discovery of Kepler-413b, a Neptune-sized circumbinary planet orbiting the eclipsing binary star system Kepler-413. The planet has an orbital period of approximately 66 days and an eccentric orbit with a semimajor axis of 0.355 AU. Analysis of the Kepler light curve revealed the planet's orbit is misaligned with the binary star plane by about 2.5 degrees, causing it to sometimes fail to transit one of the stars. The orbital configuration of the system places the planet interior to the habitable zone but its obliquity may undergo fluctuations on precession timescales.
Creation of cosmic structure in the complex galaxy cluster merger abell 2744Sérgio Sacani
Abell 2744 is one of the most actively merging galaxy clusters known, appearing to have "dark", "ghost", "bullet", and "stripped" substructures of around 1014 solar masses each. The cluster shows a complex phenomenology that will challenge simulations to reproduce. The authors present a detailed strong lensing, weak lensing, and X-ray analysis of Abell 2744, identifying 34 strongly lensed images around the massive Southern core and producing the most detailed mass map to date. They find evidence that the Southern core and Northwestern substructure are post-merger systems similar to the Bullet Cluster viewed from an angle, and derive a new constraint on the self-interaction cross section of dark matter particles. They
Shaping the glowing_eye_planetary_nebula_ngc6751Sérgio Sacani
This document presents a comprehensive study of the planetary nebula NGC 6751 using spectroscopic observations and imaging. It finds:
1) NGC 6751 has a thick equatorial ring fragmented into knots enclosing a central bubble, surrounded by faint envelope and bipolar lobes with filaments.
2) Kinematic data identify distinct velocities for different components: the outer halo at -15 km/s, inner halo at -31 km/s, and bipolar lobes at ±30 km/s.
3) A 3D morpho-kinematic model is constructed using the SHAPE code that closely matches the observed images and spectra, providing insight into the nebula's complex structure.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
The fornax deep_survey_with_vst_i_the_extended_and_diffuse_stellar_halo_of_ng...Sérgio Sacani
We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep
Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside
two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that
the core of the Fornax cluster is characterised by a very extended and diffuse envelope surrounding
the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (∼ 192 kpc)
from the galaxy center and down to μg ∼ 31 mag arcsec−2 in the g band. The deep photometry
allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399
and towards NGC 1387. By analyzing the integrated colors of this feature, we argue that it
could be due to the ongoing interaction between the two galaxies, where the outer envelope of
NGC 1387 on its east side is stripped away. By fitting the light profile, we found that exists a
physical break radius in the total light distribution at R = 10 arcmin (∼ 58 kpc) that sets the
transition region between the bright central galaxy and the outer exponential halo, and that the
stellar halo contributes for 60% of the total light of the galaxy (Sec. 3.5). We discuss the main
implications of this work on the build-up of the stellar halo at the center of the Fornax cluster.
By comparing with the numerical simulations of the stellar halo formation for the most massive
BCGs (i.e. 13 < logM200/M⊙ < 14), we find that the observed stellar halo mass fraction is
consistent with a halo formed through the multiple accretion of progenitors with stellar mass in
the range 108 − 1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through
a major merging event. The absence of a significant number of luminous stellar streams and
tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early
formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around
NGC 1399 is characterised by a more diffuse and well-mixed component, including the ICL.
Multi wavelenth observations and surveys of galaxy clustersJoana Santos
This document provides an overview of galaxy clusters, focusing on their baryonic components (intracluster medium and galaxies) and how they relate to the cluster's physical properties like mass. It discusses that galaxy clusters form hierarchically through gravitational collapse. The intracluster medium, which makes up most of the baryonic mass, emits X-rays and has been heated to temperatures of millions of degrees. The document reviews properties of the intracluster medium like density, temperature, metallicity, and how they can be measured from X-ray spectra. It also discusses upcoming surveys that will advance the study of galaxy clusters.
Modulations in the_radio_light_curve_of_the_typeiib_supernova_2001igSérgio Sacani
This document summarizes radio observations of the Type IIb supernova SN 2001ig made with the Australia Telescope Compact Array and Very Large Array over 700 days. The observations found periodic deviations from the standard model of radio light curves that are consistent with recurring density modulations in the circumstellar medium with a period of around 150 days. This provides evidence that the progenitor was a Wolf-Rayet star in a binary system with an eccentric 100 day orbit, causing regular build-up of circumstellar material. Such binary systems are thought to produce Type Ib/c supernovae through envelope stripping, linking these events to Type IIb supernovae.
1) Researchers have developed a new technique called mechanophotopatterning (MPP) that uses light irradiation and mechanical deformation to precisely control the topology of light-responsive elastomers, establishing a new patterning method.
2) Using MPP, a variety of surface topologies can be produced, making it potentially useful for applications. When optically thick samples are irradiated, they bow into 3D shapes with promising applications in advanced optics.
3) The intrinsic material properties of the polymers remain unchanged after deformation, allowing for diverse applications at the interface of cell biology and tissue engineering through dynamic control of mechanical feedback to cells.
1) The Fermi bubbles are giant gamma-ray emitting structures extending above and below the galactic center.
2) The bubbles may have been formed by periodic capture of stars by the supermassive black hole at the galactic center, releasing energy of around 3x10^52 ergs per capture.
3) This energy injection could produce very hot plasma, accelerating electrons that produce radio and gamma-ray emission through synchrotron radiation and inverse Compton scattering.
Relativistic collapse and explosion of rotating supermassive stars with therm...Sérgio Sacani
1) The document describes general relativistic simulations of collapsing supermassive stars with and without rotation using a numerical code called Nada.
2) The simulations include effects of gas pressure, radiation, electron-positron pairs, and thermonuclear energy from hydrogen and helium burning.
3) Objects with a mass of around 5×105 solar masses explode if non-rotating with a metallicity over 0.007, while rotation lowers the threshold to 0.001. More massive objects have a higher critical metallicity for explosion.
This document summarizes the results of a deep near-infrared survey of the Carina Nebula complex using the HAWK-I instrument on the VLT. The survey imaged an area of 0.36 square degrees down to magnitudes of J=23, H=22, and Ks=21, detecting over 600,000 infrared sources. Color-magnitude diagrams of the sources were analyzed to determine properties of the low-mass stellar population such as ages and masses. The survey found that about 3200 sources have masses above 1 solar mass, consistent with expectations from the initial mass function. It also found that about half of the young stars in Carina are in a widely distributed, non-clustered configuration. Six
Salts and radiation_products_on_the_surface_of_europaSérgio Sacani
The document summarizes new observations of Europa's surface using high-resolution spectroscopy. Key findings include:
1) Distinct spectral signatures of magnesium sulfate salts were detected, confined to the trailing hemisphere and correlated with radiation products like sulfuric acid and SO2.
2) On the leading hemisphere, many proposed sulfate salts could be ruled out, though distorted water ice bands were present.
3) The association of magnesium sulfate with radiation products suggests it is a radiation product rather than a constituent of an ocean brine.
4) Based on ocean chemistry models, the authors hypothesize magnesium was primarily in the form of MgCl2 prior to irradiation, and that NaCl and KCl are even more abundant and
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
1. The spectrum of the bright Kuiper Belt object 2005 FY9 is dominated by methane absorption features in the near-infrared region. However, the methane absorption lines are significantly broader than seen on any other solar system body, indicating unusually long optical path lengths through methane grains on 2005 FY9, estimated to be around 1 cm in size.
2. In addition to methane, the spectrum also shows clear evidence for ethane, which is expected to form from UV photolysis of methane. No evidence is found for nitrogen or carbon monoxide, both known to be present on Pluto.
3. The differences between 2005 FY9's spectrum and those of Pluto and 2003 UB313 are suggested
This document summarizes the discovery and analysis of a Type Ia supernova (SN Ia) at a redshift of 1.71, the most distant spectroscopically confirmed SN Ia at the time. The Hubble Space Telescope was used to obtain spectroscopy and photometry of the supernova. Analysis of the spectroscopy confirms it as a SN Ia with 92% confidence. The photometry is used to determine the supernova's distance, which agrees with the predictions of the ΛCDM cosmological model. This distant supernova helps improve constraints on the nature and behavior of dark energy in the early universe.
Este documento analiza críticamente el papel de la tecnología y la participación ciudadana en el urbanismo emergente. Propone que el urbanismo convencional ha fracasado y que el futuro está en modelos basados en redes sociales de ciudadanos que utilizan tecnologías digitales. El autor argumenta que la participación ciudadana debe entenderse como acción directa en la construcción de la ciudad, no solo como debate. El urbanismo emergente surge de forma auto-organizada a través de la interacción de grupos humanos diversos, como los que habitan las ci
Women's Worlds is an international interdisciplinary congress held every three years that focuses on research on women. The 30th anniversary event will take place July 3-7, 2011 in Ottawa-Gatineau. It is estimated that over 2,000 total participants from over 50 countries will attend, including presentations, panels, and cultural events over four days exploring the theme of "Inclusions, exclusions, and seclusions: Living in a globalized world." The University of Ottawa and Carleton University are leading partners in organizing the event.
Social business systems - success factors for Enterprise 2.0 applicationsHuddleHQ
This survey-based report examines the business drivers and adoption levels for Enterprise 2.0 technologies. It also looks at the benefits and issues being highlighted by users, and what platforms and infrastructures are being used for the delivery of social business collaboration across the enterprise. The research focuses on three specific applications - enterprise Q&A, open innovation, and sales and marketing collaboration – and makes recommendations for maximizing the benefits of social business collaboration software.
Huddle joined AIIM in this Social Business Taskforce to investigate the progress of social business technologies and underwrote the research.
The close circumstellar environment of betelgeuseSérgio Sacani
This document summarizes observations of the red supergiant star Betelgeuse and its circumstellar environment using the VLT/VISIR instrument. Diffraction-limited images were obtained in 6 filters between 7.76-12.81 μm and 2 filters between 17.65-19.50 μm. The images reveal a bright, extended, and complex circumstellar envelope at all wavelengths, pointing to the presence of oxygen-rich dust like silicates. A partial circular shell is observed between 0.5-1.0" from the star, which may correspond to the inner radius of the dust envelope. Several knots and filamentary structures are also identified within the nebula.
1) The document reports the discovery of two new circumbinary planets, Kepler-34b and Kepler-35b, orbiting binary star systems.
2) Kepler-34b orbits two sun-like stars every 289 days, while Kepler-35b orbits a pair of smaller stars every 131 days.
3) Analysis of photometric and spectroscopic data confirms the planetary nature of the transiting bodies and determines system parameters like the planets' masses and radii.
El documento reflexiona sobre la importancia de tomarse el tiempo para apreciar a las personas especiales en nuestras vidas, como amigos y seres queridos. Señala que se necesita un minuto para ver a alguien, una hora para apreciarlo, un día para amarlo y toda una vida para olvidarlo. Exhorta al lector a tomarse tiempo para vivir y valorar a sus amigos.
The document summarizes findings from a study published in Science about the detection of water ice in the protoplanetary disk surrounding the young star TW Hydrae. Using the Herschel Space Observatory, researchers detected a large reservoir of water stored as ice in the disk. This suggests icy planetesimals could form in the outer parts of the disk beyond the "snow line." The water vapor observed likely originates from ultraviolet light releasing water molecules trapped in the ice grains. The results provide insights into the distribution and transport of water in protoplanetary disks, which influenced the formation of planets like Earth.
The document lists three things that Kate Schlafly likes: animals, shopping, and winter. It provides a short list of animals, shopping, and winter without any further details about why she likes those things or examples.
The document discusses the benefits of exercise for mental health. Regular physical activity can help reduce anxiety and depression and improve mood and cognitive function. Exercise causes chemical changes in the brain that may help protect against mental illness and improve symptoms.
Este documento presenta una serie de imágenes ppt sin texto que parecen ser diapositivas de una presentación. El documento contiene 6 imágenes ppt sin información adicional.
1. In 2004, nine public libraries in Michigan formed a consortium to purchase eBooks and audiobooks through OverDrive. Each library contributed $1000 for an initial collection.
2. By 2010, the consortium had grown to 25 member libraries providing eBooks, audiobooks, and videos to patrons in multiple formats.
3. The variety of formats from OverDrive can be confusing for both library staff and patrons but the mobile access allows patrons to check out materials from any location.
The document discusses eco-friendly and sustainable fashion, including why it is important to wear such clothing. It outlines eco-friendly materials like organic cotton, soy silk, and corn fiber that are used in clothing production. The document also mentions transportation considerations and lists some eco-brands, stores, and designers that focus on sustainability, such as Levi's, H&M, Nike, and Patagonia. Ways to reuse clothing through donation are presented, as well as eco-celebrities promoting sustainable fashion.
The document discusses the benefits of exercise for mental health. Regular physical activity can help reduce anxiety and depression and improve mood and cognitive function. Exercise causes chemical changes in the brain that may help protect against mental illness and improve symptoms.
This document summarizes a study of the galaxy NGC 3801 using panchromatic data from radio, ultraviolet, optical and infrared wavelengths. The study finds that NGC 3801 is a post-merger early-type galaxy that shows evidence of recent star formation in spiral wisps as well as feedback from active galactic nucleus jets. Specifically, the galaxy has a young radio jet that has not yet impacted the outer gaseous regions, but will likely quench star formation within the next 10 million years and further transform the galaxy into a red elliptical. The multi-wavelength data reveal complex gas and dust structures that may be due to a kinematically decoupled core or warped disk.
Alma observations of_feeding_and_feedback_in_nearby_seyfert_galaxies_outflow_...Sérgio Sacani
ALMA observations of the Seyfert 2 galaxy NGC 1433 reveal a nuclear gaseous spiral structure within a nuclear ring encircling a nuclear stellar bar. Near the nucleus, there is intense high-velocity CO emission interpreted as an AGN-driven molecular outflow. The outflow involves a molecular mass of 3.6 million solar masses and a flow rate of about 7 solar masses per year. Continuum emission at the center is likely thermal dust emission from a molecular torus expected in this Seyfert 2 galaxy. The observations probe gas dynamics within 24 parsecs of the active galactic nucleus.
Alma observations of_feed_and_feedback_in_nearby_seyfert_galaxiesSérgio Sacani
The ALMA observations of NGC 1433 reveal a nuclear gaseous spiral structure within the central kpc. This spiral winds up into a pseudo-ring at ~200 pc from the center. Near the nucleus, there is intense high-velocity CO emission up to 200 km/s that is interpreted as an outflow, involving 3.6 million solar masses of molecular gas and a flow rate of ~7 solar masses per year. The outflow could be driven by both the central star formation and AGN through its radio jets. Continuum emission at 0.87 mm is detected only at the very center and likely comes from thermal dust emission from the molecular torus expected in this Seyfert 2 galaxy.
An exceptional xray_view_of_the_young_open_cluster_ngc6231Sérgio Sacani
The XMM-Newton satellite observed the young open star cluster NGC 6231 for a total of 180 kiloseconds, providing an unprecedented X-ray view. Around 600 point-like X-ray sources were detected, including many early-type O stars. The data helped refine the relationship between X-ray and bolometric luminosities for O stars, finding less scatter than previously thought, with the main exception being X-ray emission from wind interactions in binary systems. The data also provided insight into the low-mass pre-main sequence star population and star formation history of the cluster.
Three newly discovered_globular_clusters_in_ngc6822Sérgio Sacani
This document describes the discovery of three new globular clusters in the Local Group dwarf irregular galaxy NGC 6822. The authors present optical photometry of the clusters from archival CFHT/Megacam data. Two clusters are luminous and compact, while the third is a lower luminosity diffuse cluster. The positions of the new clusters are consistent with the linear alignment of previously known clusters in NGC 6822. Studying globular cluster systems in dwarf galaxies provides insights into the formation of larger galaxies through accretion and mergers.
Catch me if_you_can_is_there_a_runaway_mass_black_hole_in_the_orion_nebula_cl...Sérgio Sacani
This document describes a study investigating the dynamical evolution of the Orion Nebula Cluster through N-body simulations. The simulations assume the cluster was initially much more compact than currently observed, based on evidence that a large fraction of gas was expelled during formation. This likely led to strong few-body relaxation effects early in the cluster's evolution. The simulations find that three-body interactions among massive stars could have ejected them from the cluster while also forming a very massive object through runaway stellar mergers. This object may have collapsed directly into a massive (~100 solar mass) black hole, which could explain the velocity dispersion of stars in the Trapezium system at the cluster core. The simulations further suggest this putative black hole has a ~70
Our deep, wide-field imaging of M101 and its surrounding environment reveals:
1) M101's disk extends to nearly 25 arcminutes (50 kpc), three times the measured optical radius, with an asymmetric plume of light to the northeast following the extended HI disk.
2) This outer plume has very blue colors, suggesting a somewhat evolved young stellar population, while another redder spur is detected to the east.
3) No evidence is found of very extended tidal tails around M101 or its companions despite signs of past interactions shaping M101's asymmetry.
4) The detection of starlight at such large radii allows studying the stellar populations and star formation histories in M101's outer disk
This document summarizes observations from integral field spectroscopy of the low-luminosity Seyfert galaxy NGC 5033 using the INTEGRAL system on the William Herschel Telescope. The Hβ emission line map shows a spiral or ring-like pattern of HII regions, while the [OIII] map shows a markedly asymmetric morphology, indicating ionized gas illuminated by the active galactic nucleus. Kinematic analysis reveals important deviations between the [OIII] emitters and stellar velocity field, related to the asymmetric ionization structure. The Seyfert 1 nucleus is identified by its broad Hβ emission and located in an obscured region with the bluest spectral energy distribution.
Extended x ray emission in the h i cavity of ngc 4151- galaxy-scale active ga...Sérgio Sacani
The document summarizes the discovery of diffuse soft X-ray emission extending about 2 kpc from the active nucleus of NGC 4151, filling the cavity of H i material. The X-ray emission has a luminosity of about 1039 erg s-1 and can be fit with either a thermal plasma model with a temperature of around 0.25 keV, or a photoionized model. This interaction between the AGN and interstellar medium implies the last episode of high nuclear activity occurred relatively recently, around 104 years ago.
This document summarizes a study on the formation of polar ring galaxies through two proposed scenarios: the merging scenario and the accretion scenario. The merging scenario involves a head-on collision between two galaxies, where one becomes the host galaxy and the other's gas forms the polar ring. The accretion scenario involves tidal interactions that allow gas from one galaxy to be accreted by another galaxy to form a polar ring. Through simulations, the study finds that both scenarios can produce stable polar rings, but that the accretion scenario better matches observed properties of polar ring galaxies, such as the frequency and morphology of the rings. The study concludes the accretion scenario is both more likely and more supported by observations to explain how most polar ring galaxies form.
Asymmetrical tidal tails of open star clusters: stars crossing their cluster’...Sérgio Sacani
The document discusses asymmetrical tidal tails observed around five open star clusters, which challenges Newtonian gravity. It summarizes how tidal tails form as stars escape clusters due to energy equipartition. Observations of the Hyades, Praesepe, Coma Berenices, COIN-Gaia 13, and NGC 752 clusters found more stars in the leading tidal tails within 50 pc of the clusters. Simulations show that in Newtonian gravity, tidal tails should be symmetrical, but asymmetries can arise in Milgromian dynamics. Future work is needed to better map tidal tails and develop Milgromian simulations.
A multiband study_of_hercules_a_ii_multifrequency_vlaSérgio Sacani
This document summarizes a multi-frequency study of the radio galaxy Hercules A using the VLA radio telescope. The observations revealed that the bright jets and prominent rings have a flatter spectrum than the surrounding lobes and bridge, suggesting they represent a recent outburst from the active nucleus. The magnetic field closely follows the edges of the lobes, jets, and rings. There is also an asymmetry in the spectral properties between the two lobes that can be explained by relativistic beaming and light travel delays.
This document summarizes a study that uses cosmological simulations to model the formation of stellar halos around galaxies via the tidal disruption of accreted dwarf galaxies. The simulations follow the dynamical evolution and disruption of satellites from high redshift in a fully cosmological setting. The simulations produce stellar halos with masses and density profiles consistent with observations of the Milky Way and M31. The stellar halos show complex structures composed of well-mixed components, tidal streams, shells, and other substructures rather than smooth distributions.
This document summarizes a study using deep Chandra observations of the Seyfert 1 galaxy NGC 4151. The observations allow examination of emission line morphology in the inner 150 pc region with high spatial resolution. The maps show structures correlated with the radio outflow and optical emission. There is evidence for jet-gas cloud interactions, including regions with elevated NeIX/OVII ratios and X-ray emission exceeding expectations from nuclear photoionization alone, suggesting collisional ionization. Constraints are also placed on the spatial distribution of iron Kα emission, finding less than 5% originates beyond 150 pc, in disagreement with a prior claim of 65% from larger regions.
Solving the Multimessenger Puzzle of the AGN-starburst Composite Galaxy NGC 1068Sérgio Sacani
Multiwavelength observations indicate that some starburst galaxies show a dominant nonthermal contribution from
their central region. These active galactic nuclei (AGN)-starburst composites are of special interest, as both
phenomena on their own are potential sources of highly energetic cosmic rays and associated γ-ray and neutrino
emission. In this work, a homogeneous, steady-state two-zone multimessenger model of the nonthermal emission
from the AGN corona as well as the circumnuclear starburst region is developed and subsequently applied to the
case of NGC 1068, which has recently shown some first indications of high-energy neutrino emission. Here, we
show that the entire spectrum of multimessenger data—from radio to γ-rays including the neutrino constraint—can
be described very well if both, starburst and AGN corona, are taken into account. Using only a single emission
region is not sufficient.
This document presents aluminum abundances for about 100 red giant stars in each of the Galactic globular clusters 47 Tuc and M 4. The abundances were derived from intermediate-resolution FLAMES/GIRAFFE spectra, focusing on the Al I doublet at 8772-8773 Å. Previous homogeneous abundances of O, Na, Mg, and Si were also analyzed to study multiple stellar populations in these clusters. The data confirm two stellar populations are visible in M 4, while 47 Tuc shows evidence of at least three distinct stellar groups based on the abundances of O, Na, Mg, Al, and N.
1) NGC 474 is a lenticular galaxy surrounded by shells of matter whose origin is still debated - they could have formed from merging with a low mass galaxy or gravitational interaction with satellite galaxy NGC 470.
2) Photometric analysis of NGC 474 found its surface brightness profile is typical for a lenticular galaxy even in the center, and the color indices of the shells are consistent with NGC 474.
3) This implies the shells most likely originated from gravitational interaction with NGC 470 rather than from merging, as merging would have disturbed the central surface brightness profile.
1) NGC 474 is a lenticular galaxy surrounded by shells of matter whose origin is still debated.
2) Through surface photometry, the authors found that NGC 474's surface brightness profile is typical for a lenticular galaxy even in its central parts, and the color indices of the shells are consistent with NGC 474.
3) This implies that the shells likely originated from gravitational interaction with the nearby satellite galaxy NGC 470 rather than from the merging of two galaxies, as mergers would have disturbed NGC 474's central regions.
This paper presents a study of the extended X-ray emission in the Seyfert galaxy NGC 4151 using deep Chandra observations. Key findings include:
1) Emission line maps show strong OVII, OVIII, and NeIX line emission extending along the northeast-southwest direction, consistent with an ionization cone.
2) Spectral analysis finds the extended emission is well described by photoionized plasma models, supporting a dominant role for nuclear photoionization.
3) Faint extended emission is also seen perpendicular to the ionization cone, indicating some leakage of nuclear ionizing radiation through warm absorbers rather than being blocked by an obscuring torus.
Galaxies often interact and collide due to their close proximity. Collisions trigger intense bursts of star formation and can destroy spiral arms. Over time, collisions and mergers drive the evolution of galaxies, with giant elliptical galaxies forming from the merging of many smaller galaxies through a process called galactic cannibalism. Active galactic nuclei are powered by accretion disks around supermassive black holes, and phenomena such as jets, lobes, and broad emission lines provide evidence of black holes at the centers of galaxies.
Similar to Investigating the nuclear_activity_of_ngc1672 (20)
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
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)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
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cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
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) with
Λ
CDM. Therefore unlike low-
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Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
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counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
AppSec PNW: Android and iOS Application Security with MobSFAjin Abraham
Mobile Security Framework - MobSF is a free and open source automated mobile application security testing environment designed to help security engineers, researchers, developers, and penetration testers to identify security vulnerabilities, malicious behaviours and privacy concerns in mobile applications using static and dynamic analysis. It supports all the popular mobile application binaries and source code formats built for Android and iOS devices. In addition to automated security assessment, it also offers an interactive testing environment to build and execute scenario based test/fuzz cases against the application.
This talk covers:
Using MobSF for static analysis of mobile applications.
Interactive dynamic security assessment of Android and iOS applications.
Solving Mobile app CTF challenges.
Reverse engineering and runtime analysis of Mobile malware.
How to shift left and integrate MobSF/mobsfscan SAST and DAST in your build pipeline.
"Frontline Battles with DDoS: Best practices and Lessons Learned", Igor IvaniukFwdays
At this talk we will discuss DDoS protection tools and best practices, discuss network architectures and what AWS has to offer. Also, we will look into one of the largest DDoS attacks on Ukrainian infrastructure that happened in February 2022. We'll see, what techniques helped to keep the web resources available for Ukrainians and how AWS improved DDoS protection for all customers based on Ukraine experience
What is an RPA CoE? Session 1 – CoE VisionDianaGray10
In the first session, we will review the organization's vision and how this has an impact on the COE Structure.
Topics covered:
• The role of a steering committee
• How do the organization’s priorities determine CoE Structure?
Speaker:
Chris Bolin, Senior Intelligent Automation Architect Anika Systems
Northern Engraving | Nameplate Manufacturing Process - 2024Northern Engraving
Manufacturing custom quality metal nameplates and badges involves several standard operations. Processes include sheet prep, lithography, screening, coating, punch press and inspection. All decoration is completed in the flat sheet with adhesive and tooling operations following. The possibilities for creating unique durable nameplates are endless. How will you create your brand identity? We can help!
How information systems are built or acquired puts information, which is what they should be about, in a secondary place. Our language adapted accordingly, and we no longer talk about information systems but applications. Applications evolved in a way to break data into diverse fragments, tightly coupled with applications and expensive to integrate. The result is technical debt, which is re-paid by taking even bigger "loans", resulting in an ever-increasing technical debt. Software engineering and procurement practices work in sync with market forces to maintain this trend. This talk demonstrates how natural this situation is. The question is: can something be done to reverse the trend?
5th LF Energy Power Grid Model Meet-up SlidesDanBrown980551
5th Power Grid Model Meet-up
It is with great pleasure that we extend to you an invitation to the 5th Power Grid Model Meet-up, scheduled for 6th June 2024. This event will adopt a hybrid format, allowing participants to join us either through an online Mircosoft Teams session or in person at TU/e located at Den Dolech 2, Eindhoven, Netherlands. The meet-up will be hosted by Eindhoven University of Technology (TU/e), a research university specializing in engineering science & technology.
Power Grid Model
The global energy transition is placing new and unprecedented demands on Distribution System Operators (DSOs). Alongside upgrades to grid capacity, processes such as digitization, capacity optimization, and congestion management are becoming vital for delivering reliable services.
Power Grid Model is an open source project from Linux Foundation Energy and provides a calculation engine that is increasingly essential for DSOs. It offers a standards-based foundation enabling real-time power systems analysis, simulations of electrical power grids, and sophisticated what-if analysis. In addition, it enables in-depth studies and analysis of the electrical power grid’s behavior and performance. This comprehensive model incorporates essential factors such as power generation capacity, electrical losses, voltage levels, power flows, and system stability.
Power Grid Model is currently being applied in a wide variety of use cases, including grid planning, expansion, reliability, and congestion studies. It can also help in analyzing the impact of renewable energy integration, assessing the effects of disturbances or faults, and developing strategies for grid control and optimization.
What to expect
For the upcoming meetup we are organizing, we have an exciting lineup of activities planned:
-Insightful presentations covering two practical applications of the Power Grid Model.
-An update on the latest advancements in Power Grid -Model technology during the first and second quarters of 2024.
-An interactive brainstorming session to discuss and propose new feature requests.
-An opportunity to connect with fellow Power Grid Model enthusiasts and users.
HCL Notes and Domino License Cost Reduction in the World of DLAUpanagenda
Webinar Recording: https://www.panagenda.com/webinars/hcl-notes-and-domino-license-cost-reduction-in-the-world-of-dlau/
The introduction of DLAU and the CCB & CCX licensing model caused quite a stir in the HCL community. As a Notes and Domino customer, you may have faced challenges with unexpected user counts and license costs. You probably have questions on how this new licensing approach works and how to benefit from it. Most importantly, you likely have budget constraints and want to save money where possible. Don’t worry, we can help with all of this!
We’ll show you how to fix common misconfigurations that cause higher-than-expected user counts, and how to identify accounts which you can deactivate to save money. There are also frequent patterns that can cause unnecessary cost, like using a person document instead of a mail-in for shared mailboxes. We’ll provide examples and solutions for those as well. And naturally we’ll explain the new licensing model.
Join HCL Ambassador Marc Thomas in this webinar with a special guest appearance from Franz Walder. It will give you the tools and know-how to stay on top of what is going on with Domino licensing. You will be able lower your cost through an optimized configuration and keep it low going forward.
These topics will be covered
- Reducing license cost by finding and fixing misconfigurations and superfluous accounts
- How do CCB and CCX licenses really work?
- Understanding the DLAU tool and how to best utilize it
- Tips for common problem areas, like team mailboxes, functional/test users, etc
- Practical examples and best practices to implement right away
Introduction of Cybersecurity with OSS at Code Europe 2024Hiroshi SHIBATA
I develop the Ruby programming language, RubyGems, and Bundler, which are package managers for Ruby. Today, I will introduce how to enhance the security of your application using open-source software (OSS) examples from Ruby and RubyGems.
The first topic is CVE (Common Vulnerabilities and Exposures). I have published CVEs many times. But what exactly is a CVE? I'll provide a basic understanding of CVEs and explain how to detect and handle vulnerabilities in OSS.
Next, let's discuss package managers. Package managers play a critical role in the OSS ecosystem. I'll explain how to manage library dependencies in your application.
I'll share insights into how the Ruby and RubyGems core team works to keep our ecosystem safe. By the end of this talk, you'll have a better understanding of how to safeguard your code.
Conversational agents, or chatbots, are increasingly used to access all sorts of services using natural language. While open-domain chatbots - like ChatGPT - can converse on any topic, task-oriented chatbots - the focus of this paper - are designed for specific tasks, like booking a flight, obtaining customer support, or setting an appointment. Like any other software, task-oriented chatbots need to be properly tested, usually by defining and executing test scenarios (i.e., sequences of user-chatbot interactions). However, there is currently a lack of methods to quantify the completeness and strength of such test scenarios, which can lead to low-quality tests, and hence to buggy chatbots.
To fill this gap, we propose adapting mutation testing (MuT) for task-oriented chatbots. To this end, we introduce a set of mutation operators that emulate faults in chatbot designs, an architecture that enables MuT on chatbots built using heterogeneous technologies, and a practical realisation as an Eclipse plugin. Moreover, we evaluate the applicability, effectiveness and efficiency of our approach on open-source chatbots, with promising results.
Taking AI to the Next Level in Manufacturing.pdfssuserfac0301
Read Taking AI to the Next Level in Manufacturing to gain insights on AI adoption in the manufacturing industry, such as:
1. How quickly AI is being implemented in manufacturing.
2. Which barriers stand in the way of AI adoption.
3. How data quality and governance form the backbone of AI.
4. Organizational processes and structures that may inhibit effective AI adoption.
6. Ideas and approaches to help build your organization's AI strategy.
For the full video of this presentation, please visit: https://www.edge-ai-vision.com/2024/06/how-axelera-ai-uses-digital-compute-in-memory-to-deliver-fast-and-energy-efficient-computer-vision-a-presentation-from-axelera-ai/
Bram Verhoef, Head of Machine Learning at Axelera AI, presents the “How Axelera AI Uses Digital Compute-in-memory to Deliver Fast and Energy-efficient Computer Vision” tutorial at the May 2024 Embedded Vision Summit.
As artificial intelligence inference transitions from cloud environments to edge locations, computer vision applications achieve heightened responsiveness, reliability and privacy. This migration, however, introduces the challenge of operating within the stringent confines of resource constraints typical at the edge, including small form factors, low energy budgets and diminished memory and computational capacities. Axelera AI addresses these challenges through an innovative approach of performing digital computations within memory itself. This technique facilitates the realization of high-performance, energy-efficient and cost-effective computer vision capabilities at the thin and thick edge, extending the frontier of what is achievable with current technologies.
In this presentation, Verhoef unveils his company’s pioneering chip technology and demonstrates its capacity to deliver exceptional frames-per-second performance across a range of standard computer vision networks typical of applications in security, surveillance and the industrial sector. This shows that advanced computer vision can be accessible and efficient, even at the very edge of our technological ecosystem.
Dandelion Hashtable: beyond billion requests per second on a commodity serverAntonios Katsarakis
This slide deck presents DLHT, a concurrent in-memory hashtable. Despite efforts to optimize hashtables, that go as far as sacrificing core functionality, state-of-the-art designs still incur multiple memory accesses per request and block request processing in three cases. First, most hashtables block while waiting for data to be retrieved from memory. Second, open-addressing designs, which represent the current state-of-the-art, either cannot free index slots on deletes or must block all requests to do so. Third, index resizes block every request until all objects are copied to the new index. Defying folklore wisdom, DLHT forgoes open-addressing and adopts a fully-featured and memory-aware closed-addressing design based on bounded cache-line-chaining. This design offers lock-free index operations and deletes that free slots instantly, (2) completes most requests with a single memory access, (3) utilizes software prefetching to hide memory latencies, and (4) employs a novel non-blocking and parallel resizing. In a commodity server and a memory-resident workload, DLHT surpasses 1.6B requests per second and provides 3.5x (12x) the throughput of the state-of-the-art closed-addressing (open-addressing) resizable hashtable on Gets (Deletes).
Have you ever been confused by the myriad of choices offered by AWS for hosting a website or an API?
Lambda, Elastic Beanstalk, Lightsail, Amplify, S3 (and more!) can each host websites + APIs. But which one should we choose?
Which one is cheapest? Which one is fastest? Which one will scale to meet our needs?
Join me in this session as we dive into each AWS hosting service to determine which one is best for your scenario and explain why!
For the full video of this presentation, please visit: https://www.edge-ai-vision.com/2024/06/temporal-event-neural-networks-a-more-efficient-alternative-to-the-transformer-a-presentation-from-brainchip/
Chris Jones, Director of Product Management at BrainChip , presents the “Temporal Event Neural Networks: A More Efficient Alternative to the Transformer” tutorial at the May 2024 Embedded Vision Summit.
The expansion of AI services necessitates enhanced computational capabilities on edge devices. Temporal Event Neural Networks (TENNs), developed by BrainChip, represent a novel and highly efficient state-space network. TENNs demonstrate exceptional proficiency in handling multi-dimensional streaming data, facilitating advancements in object detection, action recognition, speech enhancement and language model/sequence generation. Through the utilization of polynomial-based continuous convolutions, TENNs streamline models, expedite training processes and significantly diminish memory requirements, achieving notable reductions of up to 50x in parameters and 5,000x in energy consumption compared to prevailing methodologies like transformers.
Integration with BrainChip’s Akida neuromorphic hardware IP further enhances TENNs’ capabilities, enabling the realization of highly capable, portable and passively cooled edge devices. This presentation delves into the technical innovations underlying TENNs, presents real-world benchmarks, and elucidates how this cutting-edge approach is positioned to revolutionize edge AI across diverse applications.
“Temporal Event Neural Networks: A More Efficient Alternative to the Transfor...
Investigating the nuclear_activity_of_ngc1672
1. D RAFT VERSION A PRIL 12, 2011
Preprint typeset using LTEX style emulateapj v. 11/10/09
A
INVESTIGATING THE NUCLEAR ACTIVITY OF BARRED SPIRAL GALAXIES: THE CASE OF NGC 1672
L. P. J ENKINS 1,2 , W. N. B RANDT 3,4 , E. J. M. C OLBERT 2 , B. KORIBALSKI 5 , K. D. K UNTZ 2 , A. J. L EVAN 6 , R. O JHA 7 , T. P. ROBERTS 8 ,
M. J. WARD 8 , A. Z EZAS 9
Draft version April 12, 2011
ABSTRACT
We have performed an X-ray study of the nearby barred spiral galaxy NGC 1672, primarily to ascertain the
arXiv:1104.1649v1 [astro-ph.CO] 8 Apr 2011
effect of the bar on its nuclear activity. We use both Chandra and XMM-Newton observations to investigate
its X-ray properties, together with supporting high-resolution optical imaging data from the Hubble Space
Telescope (HST), infrared imaging from the Spitzer Space Telescope, and ATCA ground-based radio data.
We detect 28 X-ray sources within the D25 area of the galaxy, many of which correlate spatially with star-
formation in the bar and spiral arms, while two are identified as background galaxies in the HST images. Nine
of the X-ray sources are ULXs, with the three brightest (LX > 5 × 1039 erg s−1 ) located at the ends of the
bar. With the spatial resolution of Chandra, we are able to show for the first time that NGC 1672 possesses
a hard (Γ ∼ 1.5) nuclear X-ray source with a 2–10 keV luminosity of 4 × 1038 erg s−1 . This is surrounded
by an X-ray bright circumnuclear star-forming ring, comprised of point sources and hot gas, which dominates
the 2–10 keV emission in the central region of the galaxy. The spatially resolved multiwavelength photometry
indicates that the nuclear source is a low-luminosity AGN (LLAGN), but with star formation activity close to
the central black hole. A high-resolution multiwavelength survey is required to fully assess the impact of both
large-scale bars and smaller-scale phenomena such as nuclear bars, rings and nuclear spirals on the fueling of
LLAGN.
Subject headings: galaxies: individual (NGC 1672) – galaxies: nuclei – galaxies: spiral – galaxies: evolution
1. INTRODUCTION material is also believed to build ‘pseudobulges’, which are
The presence of a bar in a galaxy plays an impor- distinct from classical galaxy bulges (Kormendy & Kennicutt
tant role in its evolution. Approximately two-thirds of 2004). A strong global density pattern such as a bar can also
all spiral galaxies are barred (e.g. Eskridge et al. 2000; produce a series of resonances between the angular velocity
Men´ ndez-Delmestre et al. 2007), so any complete picture of
e of the bar and the orbital motions of stars and gas in the disk,
galaxies must include the impact of bars on both their nu- where rings can form (Buta 1999). Indeed, some galaxies
clear and extra-nuclear properties. Secular (i.e. internal) with bars are known to have circumnuclear rings of star for-
galaxy evolution involving bars, oval distortions and spiral mation (e.g. Buta & Combes 1996; Knapen 2005a), resulting
structure can have a significant effect when a galaxy is no from increased gas density at or near the Inner Lindblad Res-
longer merging or interacting strongly with other galaxies (see onance (ILR).
Kormendy & Kennicutt 2004). For example, there is believed A question that we are addressing with this study is, can the
to be a causal connection between the existence of a bar and material driven to the center of a galaxy by the bar also fuel
a galaxy’s circumnuclear properties. Bars can drive gas from an active galactic nucleus (AGN)? While there is clear obser-
the outer disk to the inner regions of the galaxy; gas clouds vational evidence that bars in disk galaxies cause higher cen-
are shocked as they encounter the leading edge of the bar, tral concentrations of gas (and hence centrally concentrated
lose angular momentum, and flow towards the galaxy’s center star formation) compared to non-barred galaxies, it is unclear
(Shlosman et al. 1990). An observable result of this is that a whether a large-scale bar is sufficient to transport material
substantial fraction of galaxies with bars show enhanced star- close enough for AGN feeding (typically on AU scales, see
formation activity in their central regions, and the inflow of Knapen 2005b for a review). Additionally, in an X-ray study
by Maiolino et al. (1999) using Ginga, ASCA and BeppoSAX
data, a strong correlation was found between absorbing col-
1 Laboratory for X-ray Astrophysics, NASA Goddard Space Flight Cen-
umn density toward Type-2 Seyfert nuclei and the presence
ter, Code 662, Greenbelt, MD 20771, USA of a strong bar, i.e. more than 80% of Compton-thick Seyfert
2 Johns Hopkins University, 3400 N. Charles St, Baltimore, MD 21218,
USA 2s are barred. This suggests that if a low-luminosity AGN
3 Department of Astronomy & Astrophysics, The Pennsylvania State (LLAGN) is present, it may be obscured from view at optical
University, 525 Davey Lab, University Park, PA 16802, USA wavelengths and/or diluted by strong star-formation activity,
4 Institute for Gravitation and the Cosmos, The Pennsylvania State Uni-
which could lead to a misclassification as a pure star-forming
versity, University Park, PA 16802, USA
5 CSIRO, Australia Telescope National Facility (ATNF), PO Box 76, nucleus.
Epping NSW 1710, AUSTRALIA The topic of the influence of bars on galaxy evolution is
6 Department of Physics, University of Warwick, Coventry, CV4 7AL, not well studied at X-ray energies, but we are now able
UK to utilize the excellent complementary imaging and spec-
7 NVI/United States Naval Observatory, 3450 Massachusetts Ave NW,
tral capabilities of Chandra and XMM-Newton to make de-
Washington DC 20392, USA
8 Department of Physics, Durham University, South Road, Durham, tailed investigations of the X-ray characteristics of these sys-
DH1 3LE, UK tems. In particular, high-spatial-resolution X-ray observa-
9 Department of Physics, University of Crete, PO Box 2208, GR-71003 tions with Chandra provide an ideal method for search-
Heraklion, Greece ing for low-level AGN activity in nearby galaxies, in the
2. 2 Jenkins et al.
form of a hard central point source that may not be vis- ring of star formation, measuring ∼ 11′′ × 9′′ (0.9 × 0.7 kpc
ible at other wavelengths. It also allows us to separate at a distance of 16.3 Mpc), located between two ILRs. There-
potential AGN activity from other types of X-ray sources fore, studies of its nuclear properties that use large apertures
that may reside close to the nucleus, such as X-ray bina- are strongly affected by the star-formation in the ring. For
ries (XRBs) associated with circumnuclear star-formation. example, Osmer et al. (1974) showed that the optical emis-
Indeed, X-ray surveys utilizing Chandra have proved suc- sion spectrum in the central 17′′ was similar to those of
cessful in recent years in identifying previously unknown normal HII nuclei, but with an Hα/Hβ ratio indicative of
LLAGN activity in nearby galaxies. In particular, X-ray nu- a large amount of dust reddening. Storchi-Bergmann et al.
clei spanning a wide range of X-ray luminosities (∼ 1037 − (1995) also measured optical emission-line ratios in a rela-
1044 erg s−1 , 2–10 keV) have been detected in a large frac- tively large 10′′ × 20′′ aperture, and classified the nucleus as
tion (typically ∼45–70%) of galaxies hosting low-ionization ‘composite’, with ratios between those of typical starburst and
nuclear emission regions (LINERs; Heckman 1980), as well Seyfert values. More recent optical line ratio diagnostics by
as galaxies classed as having HII or transition nuclei (e.g. Kewley et al. (2000) of the emission within a ∼ 13′′ slit are
Ho et al. 2001; Terashima & Wilson 2003; Satyapal et al. indicative of an HII-type nucleus, with no Hα line broadening
2004; Satyapal et al. 2005; Dudik et al. 2005; Flohic et al. detected. All of these studies will have been strongly contam-
2006; Gonz´ lez-Mart´n et al. 2006; Gonz´ lez-Mart´n et al.
a ı a ı inated by the emission from the circumnuclear starburst ring;
2009; Zhang et al. 2009; Desroches & Ho 2009). Studies at however they do demonstrate that this component is domi-
other wavelengths have also recently been used to uncover nant, and that any potential AGN activity would be relatively
previously unknown AGN activity in nearby galaxies. For weak.
example, Spitzer infrared (IR) spectroscopic surveys have re- More detailed, spatially resolved studies have also given
vealed bonafide AGN in both LINERs and IR-bright galax- ambiguous results. Veron et al. (1981) detected possible
ies, some of which showed no sign of such activity in opti- broadening of [O III] (∼300 km s−1 ) compared to Hβ lines
cal studies (Dudik et al. 2009; Goulding & Alexander 2009). (∼150 km s−1 ) in the central 2′′ × 4′′ , which they sug-
High-resolution radio imaging has been shown to be an effi- gested was evidence of a composite HII/Seyfert 2 nu-
cient method for finding LLAGN activity; compact radio nu- cleus. Garcia-Vargas et al. (1990) performed a high-spatial-
clei have been found in 50% of LINERs/LLAGN, which are resolution spectral analysis of the nucleus, and found a strong
thought to be attributable to relativistic jets produced by ac- increase in the [O III]/Hβ ratio in the central 1′′ compared
creting super-massive black holes (Nagar et al. 2005 and ref- to its immediate surroundings. However, both lines had the
erences therein). same FWHM of ∼300 km s−1 , and the authors classified
To begin to address the nature of the nuclear (and off- the nucleus as a LINER. Storchi-Bergmann et al. (1996) also
nuclear) X-ray emission in barred galaxies, we have con- measured spatially-resolved (2′′ ) emission-line ratios, which
ducted a pilot study of the barred galaxy NGC 1672, using were better modeled by a LINER-type stellar photoionization
X-ray observations from both Chandra (40 ks) and XMM- model with Tef f ≥ 45, 000 K, rather than photoionization by
Newton (50 ks). Here we report the results from these ob- a strong AGN continuum.
servations, and use supporting HST/ACS, Spitzer and ATCA NGC 1672 has previously been observed with at X-ray
radio observations to assist in the interpretation of the X-ray wavelengths with ROSAT and ASCA. Three bright X-ray
results. This paper is laid out as follows. In § 2 we give back- sources were detected in the soft 0.2–2.0 keV band with the
ground information on the target galaxy NGC 1672. In § 3, we ROSAT HRI and PSPC, which were clearly associated with
describe the Chandra, XMM-Newton, HST/ACS, Spitzer and the galaxy (Brandt et al. 1996; de Naray et al. 2000). The
ATCA radio observations and data analysis techniques, and brightest source was located at the nucleus, and the other two
in § 4 we present our results. In § 5 we discuss the nature of were cospatial with the ends of the bar. The nucleus had a
the nuclear emission, and in § 6 we compare our results with soft X-ray spectrum consistent with thermal emission with
those for other barred and non-barred galaxies in the litera- a temperature of 0.68 keV, with a soft X-ray luminosity of
ture. Throughout this paper we use a distance to NGC 1672 7 × 1039 erg s−1 (0.2–2.0 keV). However, these studies were
of 16.3 Mpc, corresponding to a recession velocity of 1140 km again unable to resolve the nuclear emission spatially due to
s−1 relative to the centroid of the Local Group (Osmer et al. the 5′′ FWHM of the HRI point-spread-function (PSF), and
1974), with H0 =70 km s−1 Mpc−1 . so could not determine whether the bulk of the soft emission
came from a starburst or AGN. Furthermore, the ASCA data
2. NGC 1672
showed no evidence of significant hard (2–10 keV) emission
For this pilot study, we have selected the nearby (16.3 Mpc) from the nuclear source, with the hard emission in the galaxy
late-type barred spiral galaxy NGC 1672 (SB(r)bc). It being dominated by two off-nuclear X-ray sources (X-3 and
has a moderately low inclination angle (i = 34◦ , X-7, see figure 4b in de Naray et al. 2000). Thus, it was con-
de Vaucouleurs et al. 1991), and is known to have a strong cluded that if an active nucleus is present in NGC 1672, it
bar (2.4′ in length, corresponding to 11.4 kpc at a distance must be Compton-thick, with NH > 2 × 1024 cm−2 .
of 16.3 Mpc), many HII regions in its four spiral arms, plus
vigorous star formation at the ends of the bar (Brandt et al.
1996, and references therein). It has a high IR luminosity (log 3. OBSERVATIONS AND DATA REDUCTION
LF IR /L⊙ = 10.2), and a global star formation rate (SFR) of
2.7 M⊙ yr−1 (Kewley et al. 2000). 3.1. Chandra Observations
Optical studies have given conflicting evidence as to the NGC 1672 was observed with Chandra for 40 ks on April
nature of the nuclear activity in NGC 1672. It was noted 30, 2006 (ObsID 5932) using the back-illuminated S3 chip
by S´ rsic & Pastoriza (1965) as having a complex or ‘amor-
e of the Advanced CCD Imaging Spectrometer (ACIS). The
phous’ nuclear morphology, and was subsequently shown by field of view of the observation is shown in Figure 1; the
Storchi-Bergmann et al. (1996) to possess a circumnuclear nucleus of the galaxy was placed at the aimpoint of the S3
3. Investigating the nuclear activity of barred spiral galaxies 3
1’
Figure 1.DSS optical image of NGC1672 showing the Chandra ACIS-S field of view (solid red), the HST/ACS field of view
(dotted blue), and the 3- and 6-cm radio beam sizes (dashed green circles of 5.5′ and 9.8′ diameters respectively). The D25
ellipse of the galaxy is shown with a solid (black) line. The XMM-Newton and Spitzer observations cover the D25 area of the
galaxy. North is up, east to the left.
chip, and the observation encompasses the entire D25 10 ex- Initial detection of candidate sources was carried out in
tent of the galaxy. The data were initially processed with the each energy-band image using the CIAO task wavdetect,
Chandra Interactive Analysis of Observations (CIAO) tool a Mexican Hat wavelet source detection algorithm. Wavelet
suite version 3.3, with CALDB version 3.2.1. The process- scales of 1.0, 1.414, 2.0, 2.828, 4.0, 5.657 & 8.0 pixels were
ing included a charge transfer efficiency (CTI) correction and used, and the significance threshold was set to 1.0 × 10−6
time-dependent gain correction. Further data analysis was corresponding to approximately one false detection per band
performed using CIAO version 3.4. A full-field light curve over the 8×8′ field. A merged source list was created that in-
was extracted from the level-2 event list to search for periods cluded sources detected in all bands, which was used as the in-
of high background, but no strong flares were found, leaving put list for source parameterization in the ACIS Extract12
a net exposure time of 39.6 ks. IDL software (AE; Broos et al. 2010). The main steps in the
procedure are (1) the definition of source extraction regions
3.1.1. Imaging & Source Detection based on the 90% contour of the local PSF, (2) trial extrac-
tion of events within those regions, (3) improvement of po-
The basic data reduction was done using standard CIAO sitions if necessary (see below), (4) full extraction of source
data analysis threads.11 Images were created of an 8′ ×8′ and background spectra using final positions, and the creation
region (encompassing the full D25 area of the galaxy) at of associated RMFs and ARFs for each source.
full 0.492′′ pixel resolution in soft (0.3–1 keV), medium Source positions were improved (in step 3) using the
(1–2 keV), hard (2–10 keV) and broad (0.3–10 keV) energy CHECK POSITIONS stage, which computes “mean data”
bands. Monochromatic exposure maps were created at 0.8, and “correlation” positions for all sources. The “mean data”
1.0 and 2.0 keV, corresponding to the peak energy in the soft, position corresponds to the central position of the extracted in-
medium and hard band data. The images were adaptively band events in the 0.3–10 keV band, while the “correlation”
smoothed using the csmooth task, with a fairly low sig- positions are obtained by convolving the data image with a
nificance of 2σ above the local background (corresponding position-dependent model PSF. The offsets between these and
to ∼1–30 pixels in the body of the galaxy) to avoid over- the original wavdetect positions were typically 0.1–0.8′′.
smoothing of faint features in the central region (see § 4.3). The position estimates were visually reviewed, and the best
10 D
was chosen for each source. Where there was little difference
25 = the apparent major isophotal diameter measured at the surface
brightness level µB = 25.0 mag/arcsec2
11 http://asc.harvard.edu/ciao/threads/index.html 12 http://www.astro.psu.edu/xray/docs/TARA/ae users guide.html
4. 4 Jenkins et al.
between the estimates, the original position was retained. data (images and spectra) were created using standard pat-
The source extraction regions were based on the 90% con- terns corresponding to single and double pixel events for the
tour of the local PSF at the final positions. Background spec- PN (0–4), and patterns 0–12 (single to quadruple events) for
tra were extracted in local annuli, with inner radii of 1.1 times the MOS cameras. For spectral extraction, the quality flag
of the 99% radius of the PSF (to exclude any residual source was set to zero to reject events from bad pixels and events too
flux), and outer radii tailored so that each background spec- close to the CCD chip edges.
trum contains at least 100 counts. For the central (ring) re-
gion, the whole area (17′′ radius) was masked out from the 3.2.1. Imaging & Source Detection
background map due to the clumpy diffuse emission in the Multi-band source detection was performed on the PN and
area, and the background subtraction for sources in this re- MOS data, using the methods detailed in Jenkins et al. (2005).
gion (except for the nucleus) was performed using the area In brief, images were created in the following energy bands:
immediately outside this. soft (0.3–1 keV), medium (1–2 keV) and hard (2–10 keV). Ex-
Due to the complexity of the central region, the spec- posure maps were created for each instrument/energy band
trum of the nuclear X-ray source was extracted manually in using the SAS task EEXPMAP, and detector masks were cre-
CIAO using specextract. The source aperture was set ated for each camera with EMASK. Two methods of initial
to 1.2′′ radius, centered on the position from wavdetect source recognition were used: EBOXDETECT, a sliding-box
(04h45m 42.5s , −59◦ 14′ 50.1′′ ). The local background flux algorithm that simultaneously searches the three energy band
was measured in an annulus immediately outside this (1.2– images, and EWAVELET, a Mexican hat wavelet detection
2.0′′ radius), and was chosen using the radio contours as a routine that works on individual images. Both used back-
guide in order to cover as much of the area inside the ring, ground maps created with ASMOOTH. The source lists from
without encountering any ring emission (see § 4.3). Any other both methods were then parameterized using EMLDETECT,
typical non-local background region would have left residual which performs maximum likelihood PSF fits to each source.
soft emission in the nuclear source counts. These were then compared, and any additional sources de-
Since there is significant diffuse emission in the circum- tected with EWAVELET were added to the EBOXDETECT
nuclear ring area, it is possible that some of the candidate source list, and the parameterization repeated. All sources
sources detected there may be clumpy gas rather than true significant at > 4σ in at least one energy band, and within
point sources. To test this, we performed PSF fitting using the the D25 ellipse of NGC 1672, were retained and visually in-
AE task AE RADIAL PROFILE, which computes a 1-sided spected. Spectra, ARFs and RMFs were extracted from the
KS probability to determine whether the observed counts in data for each source using the SAS task especget.
the 1–2 keV energy range are consistent with the model lo- The final XMM-Newton catalog contains 19 extra-nuclear
cal 1.49 keV PSF encircled energy distribution. Six candidate sources, and their properties are listed in Table 1 along with
sources in the ring region were inconsistent with the local PSF the corresponding Chandra properties. The source fluxes
profile with a significance of > 99%. Sources without detec- were again determined using spectral fitting (see § 3.3). Note
tions in the hard 2–10 keV band and with a KS probability that six sources (including the nucleus) within the central
> 99% were deemed to be diffuse and discarded. ∼20′′ radius are not spatially resolved with XMM-Newton;
The final Chandra catalog contains 28 sources inside the these are marked with (N)=nucleus and (C)=central region
D25 ellipse, and their properties are listed in Table 1. Sources source. Apart from #10, 17 and 24, all other sources detected
with significance of > 2.5σ were retained, including faint in the Chandra observation are detected in the XMM-Newton
Chandra counterparts to two significantly detected XMM- observation.
Newton sources (for variability and completeness). This
detection threshold corresponds to >12 net source counts. 3.3. X-ray Source Spectral Fits
Source fluxes were determined using spectral fitting (see
§ 3.3). To estimate source fluxes reliably, we have performed spec-
The absolute astrometry of Chandra is generally accurate tral fitting on each source using XSPEC v12. Detailed spec-
to within ∼1′′ . 13 To confirm this, the X-ray positions were tral fitting was performed on Chandra sources with > 100 net
compared to the 2MASS point source catalog. Three coun- counts, and on XMM-Newton sources with > 100 net counts
terparts were found in the field; the offsets between the X-ray in either the PN or MOS data. These spectra were binned
and 2MASS positions were small (0.14, 0.16 & 0.6′′ ), and in (grouped to a minimum of 20 counts per bin) and fitted, using
non-uniform directions, with the greatest offset for a source χ2 statistics, with both powerlaw+absorption (PO*WABS)
4′ off-axis at the edge of the field. Given this accuracy, no and disk blackbody+absorption (DISKBB*WABS) models.
astrometric correction was made to the Chandra positions. In all cases, the powerlaw model provided the best fit. Spec-
tral parameters and corresponding 0.3–10 keV fluxes and lu-
3.2. XMM-Newton Observations minosities are shown in Table 1. For the XMM-Newton data,
NGC 1672 was observed with XMM-Newton for 50 ks on the PN, MOS1 and MOS2 spectra were fitted simultaneously.
November 27, 2004 (ObsID 0203880101). The EPIC MOS- The fluxes and errors from the three instruments were com-
1, MOS-2 and PN cameras were operated with medium filters bined to provide a weighted mean flux for each source using
in Prime Full Window mode. Full-field light curves were ac- the method of Barlow (2004).14
cumulated for the three exposures in the 10–15 keV band to For sources with < 100 net counts, a simple power-
check for high background intervals of soft proton flares. The law+Galactic absorption model was fitted to unbinned spec-
data were found to be clean for the duration of the observa- tra using the C-statistic (Cash 1979). Since at such low
tion, and the full time intervals were used in subsequent anal- count rates source parameters are difficult to constrain, the
ysis: 47.9 ks (PN), 49.4 ks (MOS1) & 49.5 ks (MOS2). All powerlaw and absorption parameters were frozen (Γ = 1.7,
13 http://cxc.harvard.edu/cal/ASPECT/celmon/ 14 http://www.slac.stanford.edu/∼barlow/statistics.html
5. Investigating the nuclear activity of barred spiral galaxies 5
NHGal = 0.223 × 1021 cm−2 ), with the normalization as the An alternative to direct PSF subtraction is to use a nar-
only free parameter. The resulting fluxes and luminosities are row aperture for the determination of the light within the nu-
also shown in Table 1. The source properties are described in cleus, and then to apply the aperture corrections tabulated by
§ 4.1. Sirianni et al. (2005). We used a 0.1′′ (2 pixel) radius aper-
ture, and subtracted the background using an 1.2–2′′ annulus
3.4. Multi-wavelength data centered on the nucleus. To compare directly with the Chan-
3.4.1. HST-ACS Observations dra observations, we have also performed photometry using
the same physical aperture (1.2′′ radius) and background an-
NGC 1672 was observed by the Hubble Space Telescope nulus (again 1.2–2′′ ). The resulting magnitudes from these
(HST) on August 1, 2005 using the Advanced Camera for methods are also shown in Table 2.
Surveys (ACS) Wide Field Channel (WFC) in the broad- The upper limits measured using the PSF subtraction
band F435W, F550M and F814W filters, plus the narrow-band method are similar to the measurements obtained from the
F658N (Hα) filter. A large dither was implemented, covering narrow aperture, though there is a good deal of scatter be-
the dimensions of one of the WFC chips in order to fit the vis- tween these and the larger Chandra aperture measurements.
ible disk of the galaxy into each observation (see Figure 1). Given that PSF subtraction gives the most stringent con-
Exposure times were 2444 s in each observation, split into straints on the magnitude of a nuclear point source, we adopt
four separate observations corresponding to the visibility of these limits for the multiwavelength comparison (see Table 3),
NGC 1672 in each single orbit. We also include in our analy- and the construction of the nuclear spectral energy distribu-
sis an archival ACS High Resolution Channel (HRC) F330W tion (SED, see § 5.2). The AB magnitudes were converted
UV observation of the nucleus of NGC 1672, taken July 19, to flux density using ABmag = −2.5 log Fν − 48.6,16 and
2002, with an exposure time of 1140 s. All of the ACS ob- then into luminosity using νLν = 4πd2 Fν ×Central filter fre-
servations were processed through the standard multidrizzle quency.17 We note that the centroid of the emission in the
pipeline (Koekemoer et al. 2002). As sub-pixel dithers were F330W images does not correspond with that seen in data
not used in the observations, the drizzle parameters pixfrac taken at longer wavelengths, which suggests that there is some
and scale were set to unity, preserving the native pixel scale of extinction along the line-of-sight.
both the HRC and WFC. Each of the ACS WFC images were
astrometrically registered with 2MASS stellar objects falling 3.4.2. Spitzer IR Observations
within the FOV, yielding an astrometric fit with an RMS of
∼ 0.15′′ . The F658N image is significantly contaminated by NGC 1672 was observed with the Spitzer Infrared Ar-
continuum emission within the Hα passband; we therefore ray Camera (IRAC, Fazio et al. 2004) on November 29 2006
created a continuum-subtracted image (denoted F658CS) us- (Program ID 30496, PI Fisher). Basic Calibrated Data (BCD)
ing a continuum image estimated from a linear combination of were retrieved from the archive at 3.6, 4.5, 5.8 and 8.0µm.
the F550M and F814W images (weighted by their separation We performed post-BCD processing (mosaicing, with a plate
from the Hα line, and multiplied by the relative sensitivity of scale of 0.86 arcsec/pixel) using the Spitzer data-processing
each filter to obtain the same physical units in each image). package MOPEX (Makovoz et al. 2006). The images are flux
The ACS images have a very high spatial resolution of calibrated in the pipeline in units of surface brightness (MJy
∼0.1′′ . They show that, while the optical emission peaks sr−1 ), and we converted them to flux density units by mul-
in the central 2′′ nuclear region, it is clearly non-point like tiplying by a conversion factor of 1MJy sr−1 = 17.38 µJy
with a FWHM of ∼30 pixels (1.5′′ ). Indeed it displays a per pixel. This is a combination of the conversion given in
complex/irregular morphology, and in a visual inspection we the Spitzer Observers Manual (1MJy sr−1 = 23.50443 µJy
found no obvious point sources that could correspond to, arcsec−2 ), and the pixel solid angle (0.74 arcsec2 ). A MIPS
for example, a nuclear star cluster (which are generally only (multi-band imaging photometer) 24µm calibrated image was
“marginally resolved ” in HST images of nearby galaxies, also retrieved from the archive (from the same Spitzer pro-
B¨ ker et al. 2004). The complexity and extended nature of
o gram), which was reduced using standard pipeline processing.
the region suggests that the use of any moderate sized photo- A stellar-continuum subtracted 8.0µm (PAH) image was cre-
metric aperture will result in a significant overestimate of the ated to highlight the star-forming regions, using a conversion
true flux from the nucleus. We investigated this in three ways: based on a standard model of the starlight near-IR SED; this
(1) via PSF subtraction, (2) narrow aperture photometry, and is 8.0µm − 0.232×3.6µm (Helou et al. 2004).
(3) photometry using the Chandra aperture. Photometry was performed on the nuclear source in the four
′′
To estimate the maximum magnitude of any point source at IRAC bands using a 1. 5 radius aperture centred on the Chan-
the center of the galaxy, PSFs were constructed from isolated dra position of the nucleus, using a local annular background
point sources in each image and subtracted from the centroid between 2.5–3.0′′. This aperture was chosen because of the
of the galaxy light in each band, scaled such that their cores larger PSF of IRAC (1.4–1.7′′ FWHM, Fazio et al. 2004), and
resulted in a roughly zero flux value for the brightest pixel aperture corrections were applied as detailed in the IRAC
in the galaxy core. For two filters it was not possible to ob- Data Handbook v3.0, section 5.5.1. The resulting flux den-
tain actual PSFs from the images. In the case of F330W, the sities (and AB magnitudes) are shown in Table 3. Note that
HRC field of view is too small for any bright, isolated sources photometry is not performed on the MIPS data, as the spatial
to be present, while in our F658N continuum-subtracted im- resolution (∼6′′ ) is insufficient to separate the nuclear source
age the stars were largely subtracted. To overcome this, we from the circumnuclear ring emission.
used TinyTim15 to create artificial PSFs for these filters, which
were then subtracted from the data. The resulting upper limits 3.4.3. Radio Observations
are shown in Table 2.
16 http://www.stsci.edu/hst/acs/analysis/zeropoints
15 http://www.stecf.org/instruments/TinyTim/ 17 http://acs.pha.jhu.edu/instrument/filters/general/Master Table.html
6. 6 Jenkins et al.
Chandra XMM
1’ (a) 1’ (b)
Spitzer Chandra
(diffuse)
1’ (c) 1’ (d)
Figure 2. (a) Chandra 3-color ACIS-S image of NGC 1672: red = 0.3–1 keV, green = 1–2 keV, blue = 2–10 keV. (b) XMM-Newton
EPIC (MOS1+MOS2+PN) 3-color image (in the same energy bands). (c) Spitzer 3-color image: red = 24µm (MIPS), green =
8µm (IRAC), blue = 3.6µm (IRAC). (d) Chandra 3-color image of the diffuse X-ray emission. Contours from the Spitzer IRAC
stellar-continuum-subtracted 8µm data are overlaid, which are spatially correlated with the X-ray emission. The D25 ellipse of
the galaxy is shown with a dashed white line. All images are on the same scale and co-aligned. North is up, east to the left.
Radio continuum observations of NGC 1672 were ob- at 4800 MHz and 4928 MHz, with bandwidths of 128 MHz
tained at 3-cm and 6-cm with the Australia Telescope Com- divided into 32 channels. At 4864 MHz the ATCA primary
pact Array (ATCA). Data reduction was carried out with the beam is 9.8′ . The data from both frequency bands were com-
MIRIAD 18 software package, using standard procedures. bined, resulting in an angular resolution of 1.9′′ ×1.7′′ and an
The 3-cm image was created using archival data from a rms of 0.04 mJy/beam. The source PKS B1934–638 was used
1.5C configuration obtained in May 2003 and a 6D configura- as the primary (amplitude & bandpass) calibrator, and PKS
tion obtained in July 2003, with on-source integration times B0522–611 and PKS B0420–625 were used as the secondary
of 9 h and 10 h respectively. Both observations consist of (phase) calibrators at 3- and 6-cm, respectively.
two frequency bands centered at 8640 MHz and 8768 MHz, A point source fit to the nuclear source gives a position
with bandwidths of 128 MHz divided into 32 channels. At of α, δ(J2000) = 04h 45m 42.50s, −59◦ 14′ 49.85′′ (±0.12′′).
8700 MHz the ATCA primary beam is 5.5′ . The data for We measure peak fluxes of 0.95 ± 0.15 mJy at 3-cm and
both observations/frequency bands were combined using ‘ro- 1.62±0.15 mJy at 6-cm. We measure integrated flux densities
bust’ weighting (r = 0), resulting in an angular resolution of 34 mJy (3-cm) and 35 mJy (6-cm) for the radio continuum
of 1.3′′ ×1.0′′ and an rms of 0.03 mJy/beam. The 6-cm im- emission from both the nuclear source and surrounding star-
age was created using archival data in the 6A configuration forming ring. It is likely that some extended flux has been
obtained in May 2002, with an on-source integration time of resolved out by the interferometer. Single-dish radio contin-
11 h. The observation consists of two frequency bands centred uum flux estimates of NGC 1672 (PMN J0445–5914, PKS
J0445–5915) at ∼5 GHz (6-cm) are typically around 100 mJy
18 http://www.atnf.csiro.au/computing/software/miriad/ (see Wright et al. 1994; Harnett 1987).
7. Investigating the nuclear activity of barred spiral galaxies 7
Figure 3.HST/ACS 3-color image of NGC 1672, produced by Zolt Levay at the Space Telescope Science Institute. The colors
correspond to: red=combined F658N (Hα) + F814W (I), green = F550M (V ), blue = F435W (B). The image is 4.4′ × 3.2′ in
size, with an orientation such that north is 34◦ east (left) of the y-axis.
There is also one other radio source in the field of view at detected within the D25 area of the galaxy (blue crosses).
α, δ(J2000) = 04h 45m 36.70s, −59◦ 14′ 28.00′′ (±0.03′′), with Note that we do not plot the source positions on the HST im-
flux densities of 1.5 ± 0.1 mJy (3-cm) and 1.4 ± 0.1 mJy (6- age here since it does not cover the entire D25 area. The po-
cm). This is positionally coincident with X-ray source #8 sitions correlate well with the optical structure of the galaxy,
(044536.73–591428.0). with sources concentrated in the nuclear region (see § 4.3) and
spread throughout the disk and spiral arms. The extra-nuclear
4. RESULTS source fluxes range between FX = 2.3 × 10−15 − 2.8 × 10−13
Figure 2(a–c) shows 3-color Chandra, XMM-Newton and erg s−1 cm−2 over both XMM-Newton and Chandra observa-
Spitzer IRAC images of the entire D25 area of NGC 1672. tions, corresponding to LX = 7.4 × 1037 − 9.0 × 1039 erg
The X-ray sources outside the nuclear region are well re- s−1 at the distance of NGC 1672.
solved in both the Chandra and XMM-Newton data, and are Nine sources, almost a third of the population, reach ul-
discussed in § 4.1. There is also a diffuse hot X-ray gas com- traluminous X-ray source (ULX) luminosities (LX > 1039
ponent, which is shown in Figure 2(d) as extended red/green erg s−1 , 0.3–10 keV) in either one or both X-ray observa-
X-ray emission (see § 4.2). The nuclear region is very bright tions; these are marked with red circles (sources 1, 4, 5, 6,
at all wavelengths, and will be discussed in detail in § 4.3. 7, 13, 24, 25 and 28). Three of the ULXs are very bright
The Spitzer IR data show that the majority of the non-nuclear (sources 4, 5, and 25 with LX > 5 × 1039 erg s−1 , marked
star-formation activity is confined to the bar and inner spiral with larger circles), and are co-spatial with the ends of the
arms (illustrated in red and green), whereas older stellar pop- bar (as previously noted by Brandt et al. 1996). This is con-
ulations are spread throughout the disk (illustrated in blue). sistent with models that show that gas can accumulate at the
Figure 3 shows the high-resolution 3-color HST/ACS image, tips of bars due to the corotation of the bar structure with
where the bar structure, numerous HII regions and dust lanes the disk (Englmaier & Gerhard 1997), thereby creating star-
are visible. forming regions where X-ray binaries can form. Other exam-
ples of this phenomenon have been observed in the barred
4.1. X-ray Point Source Population galaxies NGC 7771 (Jenkins et al. 2005) and NGC 4303
(Jim´ nez-Bail´ n et al. 2003).
e o
Figure 4 (top left) shows the DSS optical image of
Figure 4 (top right) shows the source positions overlaid on
NGC 1672, overlaid with the positions of the 28 X-ray sources
8. 8 Jenkins et al.
DSS Spitzer 8µm
1’ 1’
s26 s8
Figure 4.Top left: DSS optical image of NGC1672 with the 28 X-ray source positions marked with blue crosses. Sources with
LX > 1039 erg s−1 in the 0.3–10 keV band (i.e. ULXs) in either the XMM-Newton or Chandra observation are marked with red
circles, with the 3 brightest (LX > 5 × 1039 erg s−1 ) denoted by larger circles (#4, 5 & 25). Sources that show variability of
> 2.5σ between the two observations are also marked with white squares (including sources detected in only one observation).
The dotted diamonds denote sources #8 & 26, which are resolved as background galaxies in the optical HST/ACS images; these
are shown in the lower panel, where the diamond boxes are 2′′ × 2′′ centered on the X-ray positions. Top right: the Spitzer IRAC
continuum-subtracted 8µm image, showing the locations of the X-ray sources with respect to star-forming regions in the galaxy.
the Spitzer 8µm image, illustrating the coincidence of many Figure 4 (top left) also denotes variable sources (marked
X-ray sources with regions of star-formation in the bar and with white squares). Six sources show significant long-term
inner spiral arm regions. We have correlated the X-ray source flux variability between the XMM-Newton and Chandra ob-
positions with the HII region catalog of Evans et al. (1996). servations at levels of > 2.5σ; these are sources 1, 4, 6, 8, 21
Taking into account both the absolute astrometric accuracy of and 25. Most notable are the increases in flux in two of the
the X-ray and HII region positions (∼1′′ combined) as well as brightest ULXs in the Chandra observations; #4 increases by
the measured areas of the HII regions, we associate eleven X- a factor of ∼5 (up to 6.9 × 1039 erg s−1 ), and #25 increases
ray sources with HII regions (2, 4, 5, 7, 13, 14, 18, 21, 25, 27, by a factor of ∼3 (up to 9.0 × 1039 erg s−1 ), indicating that
and 28). These include the three brightest ULXs, and three the high luminosity of these sources is not due to confusion
sources in the circumnuclear ring. of several fainter sources. These flux increases are accompa-
We have not performed any complex spectral fitting on the nied by a spectral hardening of source #4, but no significant
X-ray sources, as even the brightest are well-fit with simple spectral change in source #25. The other four sources with
2
absorption+powerlaw models, with χν close to 1 (see Ta- spectral fits in both observations show no significant spectral
ble 1). The spectra and model fits are shown in Figures 5 change between observations. Another four sources (10, 17,
and 6. However, we note that even though this simple model 24 and 27) are only detected in one observation.
provides acceptable empirical fits to these data, this is likely To investigate longer-term behavior, in Table 4 we show
due to the relatively low photon counts ( 2000 counts, total a comparison between XMM-Newton, Chandra and ROSAT
PN+MOS or ACIS-S), and the true underlying spectral shapes HRI soft X-ray luminosities for five sources detected in
are likely to be more complex (see Stobbart et al. 2006 for a all three observations. We quote the 0.2–2 keV HRI lu-
discussion). minosities from de Naray et al. (2000) for the combined
9. Investigating the nuclear activity of barred spiral galaxies 9
Normalization (count s−1 keV−1)
Normalization (count s−1 keV−1)
Normalization (count s−1 keV−1)
0.01
S1 S4 S5
2×10−4 5×10−4 10−3 2×10−3
0.01
10−3
10−3
10−4
1.5
1.5
1.5
Ratio
Ratio
Ratio
1
1
1
0.5 1 2 5 10 0.5 1 2 5 10 0.5 1 2 5 10
Energy (keV) Energy (keV) Energy (keV)
2×10−4 5×10−4 10−32×10−3 5×10−3
Normalization (count s−1 keV−1)
Normalization (count s−1 keV−1)
Normalization (count s−1 keV−1)
S6 S7 S19
5×10−4 10−3 2×10−3
10−3
10−4
2×10−4
2
1.5
1.5
1.5
Ratio
Ratio
Ratio
1
1
1
0.5 1 2 5 10 0.5 1 2 5 10 0.5 1 2 5 10
Energy (keV) Energy (keV) Energy (keV)
10−4 2×10−4 5×10−4 10−3 2×10−3
Normalization (count s−1 keV−1)
Normalization (count s−1 keV−1)
Normalization (count s−1 keV−1)
S22 S25
0.01
S26
10−3
10−3
10−4
10−4
1.5
1.5
1.5
Ratio
Ratio
Ratio
1
1
1
0.5
0.5 1 2 5 10 0.5 1 2 5 10
Energy (keV) Energy (keV) 0.5 1 2 5 10
Energy (keV)
Normalization (count s−1 keV−1)
Normalization (count s−1 keV−1)
10−42×10−4 5×10−4 10−32×10−3
S27 S28
10−3
10−4
1.5
1.5
Ratio
Ratio
1
1
0.5 1 2 5 10 0.5 1 2 5 10
Energy (keV) Energy (keV)
XMM-Newton EPIC spectra of the 11 sources with > 100 net PN or MOS counts. PN data points and power-
Figure 5.
law+absorption models are shown in green; those of the MOS data are shown in red/black.
1992/1997 dataset (which gives better photon statistics), to- We estimate the number of background X-ray sources in the
gether with 0.2–2 keV luminosities derived from the best- D25 area of NGC 1672 using the hard-band (2–10 keV) log
fit XMM-Newton and Chandra spectral models corrected for N -log S source distributions from Chandra deep field studies
Galactic absorption. Note that we also include #23 (ROSAT (we do not use the soft-band log N -log S since the detec-
source X-5), which was originally believed to be coincident tion sensitivity at soft energies will be affected by absorption
with a foreground star given the ROSAT positional errors by neutral material in the galactic disk). Using a source de-
(∼5′′ ). However, with the Chandra positional accuracy of tection threshold of 12 counts in the 0.3–10 keV band (corre-
∼0.5′′ , we show that this source is not consistent with the sponding to the faintest source detected in the Chandra ob-
2MASS position of the star (04h 45m49.54s , −59◦12′ 54.1′′) servation), and converting this to a 2–10 keV flux for a typi-
with an offset of ∼5′′ . In fact, this is the source that shows the cal AGN (∼ 1.5 × 10−15 erg s−1 cm−2 , using Γ = 1.7 and
largest long-term variability with Lhigh /Llow = 3.6 over this NHGal = 0.223 × 1021 cm−2 ), the log N -log S relations of
∼10 year period. The remaining sources vary in luminosity Giacconi et al. (2001), Campana et al. (2001) and Bauer et al.
by factors of 1 − 3. (2004) all predict between 2–3 background sources in the
10. 10 Jenkins et al.
5×10−4 10−3 2×10−3 5×10−3 0.01 0.02
10−3 2×10−3 5×10−3 0.01 0.02
Normalization (count s−1 keV−1)
Normalization (count s−1 keV−1)
Normalization (count s−1 keV−1)
S1 S4
10−3
S5
5×10−4
2×10−4
1.5
1.5
1.5
Ratio
Ratio
Ratio
1
1
1
0.5 1 2 5 10 0.5 1 2 5 10
Energy (keV) Energy (keV) 0.5 1 2 5 10
Energy (keV)
5×10−4 10−3 2×10−3 5×10−3 0.01
2×10−4 5×10−4 10−32×10−3 5×10−3
2×10−3
Normalization (count s−1 keV−1)
Normalization (count s−1 keV−1)
Normalization (count s−1 keV−1)
S7 S13
S24
10−3
5×10−4
1.5
1.5
1.5
Ratio
Ratio
Ratio
1
1
1
0.5 1 2 5 10 0.5 1 2 5 10
Energy (keV) Energy (keV) 0.5 1 2 5 10
Energy (keV)
Normalization (count s−1 keV−1)
Normalization (count s−1 keV−1)
2×10−3
S25 S28
0.01
10−3
10−3
5×10−4
1.5
1.5
Ratio
Ratio
1
1
0.5 1 2 5 10 0.5 1 2 5 10
Energy (keV) Energy (keV)
Figure 6. Chandra ACIS-S spectra of the 8 sources with > 100 net counts, together with the powerlaw+absorption models.
field. Note that this is in fact an upper limit, since the contours from the continuum-subtracted Spitzer IRAC 8.0µm
NGC 1672 source catalog is not corrected for incompleteness. image, which highlights star-formation activity; the diffuse
Inspection of the HST/ACS images allows us to identify two emission is spatially correlated with the IR emission, follow-
X-ray sources as background galaxies immediately; these are ing the bar/inner spiral arm structure.
#26, which appears to be a face-on disk galaxy with a bright A source spectrum was extracted from an elliptical region
nucleus, and #8, which looks like an edge-on galaxy with vis- (a, b) = (2.25′ , 1.11′ ) centered on the nucleus with a posi-
ible dust lanes seen through the disk of NGC 1672 (see Fig- tion angle of 90◦ . The detected point sources were excluded
ure 4, lower panel). As noted in § 3.4.3, source #8 is the only (using regions with twice the radius of the 90% encircled en-
extra-nuclear X-ray source with a detected radio counterpart. ergy ellipses), as well as the innermost 20′′ radius circumnu-
At the distance of NGC 1672, the 2–10 keV X-ray luminos- clear ring region. The background regions were chosen to be
ity (at its brightest in the XMM-Newton observation) would (1) the region on the ACIS-S3 chip outside the D25 radius
be LX = 7.9 × 1038 erg s−1 , and the 5 GHz radio luminosity and not containing point sources, and (2) the region on the
would be νLν = 2.2 × 1036 erg s−1 . According to the X- ACIS-S1 chip not containing bright point sources. To further
ray/radio fundamental plane of Merloni et al. (2003), this is constrain the soft end of the background emission, we also
inconsistent with emission from a stellar mass black hole (i.e. used the seven element ROSAT All Sky Survey (RASS) spec-
too radio-bright), and supports the hypothesis that this source tral energy distribution (Snowden et al. 1997) from an annulus
is a background AGN (see § 5 for further discussion of this 30′ < R < 1◦ around NGC 1672, extracted using the X-ray
relation with regards to the nuclear source). background web tool hosted by the HEASARC19 . For each
Chandra spectrum, we created a particle background spec-
4.2. Diffuse X-ray Emission
trum using the “stowed” data from the appropriate chip and
We have used the Chandra observation to study the diffuse mode, scaled to produce the same 10–13 keV band count rate
X-ray component of NGC 1672 due to its ∼1′′ spatial resolu- as observed in the ObsID 5932 data. The particle background
tion, and hence ease of source subtraction. The morphology spectra were then used as the “background” spectra within
of the diffuse emission is illustrated in Figure 2 (d), where the XSPEC, and the spectra of the galaxy and the remainder of the
X-ray point sources and central ring region have been masked,
19 http://heasarc.gsfc.nasa.gov/cgi-bin/Tools/xraybg/xraybg.pl
and the residual emission adaptively smoothed. Overlaid are