The document discusses revisiting measurements of the integrated Sachs-Wolfe (ISW) effect in light of new data. It updates the data set used in a previous study to include the latest cosmic microwave background and large-scale structure data. Testing finds the updated results are consistent with previous measurements, with the combined ISW detection significance being 4.4 sigma. The paper also addresses criticisms raised about potential systematic errors, focusing on a rotation test of maps, but finds no evidence of additional contamination.
45 Evidence for a narrow N* (1685) resonance in quasifree Compton scattering ...Cristian Randieri PhD
Evidence for a narrow N* (1685) resonance in quasifree Compton scattering on the neutron - The American Physical Society, Physical Review C, February 2011, Vol. 83, N. 2, pp. 022201-1-022201-4, ISSN: 0556-2813, doi: 10.1103/PhysRevC.83.022201
di V. Kuznetsov, M. V. Polyakov, V. Bellini, T. Boiko, S. Chebotaryov, H.-S. Dho, G. Gervino, F. Ghio, A. Giusa, A. Kim, W. Kim, F. Mammoliti, E. Milman, A. Ni, I. A. Perevalova, C. Randieri, G. Russo, M. L. Sperduto, C. M. Sutera, A. N. Vall (2011)
Abstract
The study of quasifree Compton scattering on the neutron in the energy range of Eγ=0.75–1.5 GeV is presented. The data reveal a narrow peak at W~1.685 GeV. This result, being considered in conjunction with the recent evidence for a narrow structure at W~1.68 GeV in η photoproduction on the neutron, suggests the existence of a nucleon resonance with unusual properties: a mass M~1.685GeV, a narrow width Γ⩽30 MeV, and the much stronger photoexcitation on the neutron than on the proton.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
Past studies have identified a spatially extended excess of ∼1-3 GeV gamma rays from the region
surrounding the Galactic Center, consistent with the emission expected from annihilating dark
matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics
and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails
of the point spread function and generate high resolution gamma-ray maps, enabling us to more
easily separate the various gamma-ray components. Within these maps, we find the GeV excess
to be robust and highly statistically significant, with a spectrum, angular distribution, and overall
normalization that is in good agreement with that predicted by simple annihilating dark matter
models. For example, the signal is very well fit by a 36-51 GeV dark matter particle annihilating to
b
¯b with an annihilation cross section of σv = (1−3)×10−26 cm3
/s (normalized to a local dark matter
density of 0.4 GeV/cm3
). Furthermore, we confirm that the angular distribution of the excess is
approximately spherically symmetric and centered around the dynamical center of the Milky Way
(within ∼0.05◦
of Sgr A∗
), showing no sign of elongation along the Galactic Plane. The signal is
observed to extend to at least ' 10◦
from the Galactic Center, disfavoring the possibility that this
emission originates from millisecond pulsars.
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
A magnetar-powered X-ray transient as the aftermath of a binary neutron-star ...Sérgio Sacani
Mergers of neutron stars are known to be associated with short γ-ray
bursts1–4
. If the neutron-star equation of state is sufficiently stiff
(that is, the pressure increases sharply as the density increases), at
least some such mergers will leave behind a supramassive or even a
stable neutron star that spins rapidly with a strong magnetic field5–8
(that is, a magnetar). Such a magnetar signature may have been
observed in the form of the X-ray plateau that follows up to half
of observed short γ-ray bursts9,10. However, it has been expected
that some X-ray transients powered by binary neutron-star mergers
may not be associated with a short γ-ray burst11,12. A fast X-ray
transient (CDF-S XT1) was recently found to be associated with a
faint host galaxy, the redshift of which is unknown13. Its X-ray and
host-galaxy properties allow several possible explanations including
a short γ-ray burst seen off-axis, a low-luminosity γ-ray burst at
high redshift, or a tidal disruption event involving an intermediatemass black hole and a white dwarf13. Here we report a second X-ray
transient, CDF-S XT2, that is associated with a galaxy at redshift
z = 0.738 (ref. 14). The measured light curve is fully consistent with
the X-ray transient being powered by a millisecond magnetar. More
intriguingly, CDF-S XT2 lies in the outskirts of its star-forming host
galaxy with a moderate offset from the galaxy centre, as short γ-ray
bursts often do15,16. The estimated event-rate density of similar
X-ray transients, when corrected to the local value, is consistent
with the event-rate density of binary neutron-star mergers that is
robustly inferred from the detection of the gravitational-wave event
GW170817.
No large population of unbound or wide-orbit Jupiter-mass planets Sérgio Sacani
Planet formation theories predict that some planets may be ejected from their parent systems as result of dynamical interactions and other processes1–3. Unbound planets can also be formed through gravitational collapse, in a way similar to that in which stars form4. A handful of free-floating planetary-mass objects have been discovered by infrared surveys of young stellar clusters and star-forming regions5,6 as well as wide-field surveys7, but these studies are incomplete8–10 for objects below five Jupiter masses. Gravitational microlensing is the only method capable of exploring the entire population of free-floating planets down to Mars-mass objects, because the microlensing signal does not depend on the brightness of the lensing object. A characteristic timescale of microlensing events depends on the mass of the lens: the less massive the lens, the shorter the microlensing event. A previous analysis11 of 474 microlensing events found an excess of ten very short events (1–2 days)—more than known stellar populations would suggest—indicating the existence of a large population of unbound or wide-orbit Jupiter-mass planets (reported to be almost twice as common as main-sequence stars). These results, however, do not match predictions of planet-formation theories3,12 and surveys of young clusters8–10. Here we analyse a sample of microlensing events six times larger than that of ref. 11 discovered during the years 2010–15. Although our survey has very high sensitivity (detection efficiency) to short-timescale (1–2 days) microlensing events, we found no excess of events with timescales in this range, with a
95 per cent upper limit on the frequency of Jupiter-mass freefloating or wide-orbit planets of 0.25 planets per main-sequence star. We detected a few possible ultrashort-timescale events (with timescales of less than half a day), which may indicate the existence of Earth-mass and super-Earth-mass free-floating planets, as predicted by planet-formation theories3,12.
45 Evidence for a narrow N* (1685) resonance in quasifree Compton scattering ...Cristian Randieri PhD
Evidence for a narrow N* (1685) resonance in quasifree Compton scattering on the neutron - The American Physical Society, Physical Review C, February 2011, Vol. 83, N. 2, pp. 022201-1-022201-4, ISSN: 0556-2813, doi: 10.1103/PhysRevC.83.022201
di V. Kuznetsov, M. V. Polyakov, V. Bellini, T. Boiko, S. Chebotaryov, H.-S. Dho, G. Gervino, F. Ghio, A. Giusa, A. Kim, W. Kim, F. Mammoliti, E. Milman, A. Ni, I. A. Perevalova, C. Randieri, G. Russo, M. L. Sperduto, C. M. Sutera, A. N. Vall (2011)
Abstract
The study of quasifree Compton scattering on the neutron in the energy range of Eγ=0.75–1.5 GeV is presented. The data reveal a narrow peak at W~1.685 GeV. This result, being considered in conjunction with the recent evidence for a narrow structure at W~1.68 GeV in η photoproduction on the neutron, suggests the existence of a nucleon resonance with unusual properties: a mass M~1.685GeV, a narrow width Γ⩽30 MeV, and the much stronger photoexcitation on the neutron than on the proton.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
Past studies have identified a spatially extended excess of ∼1-3 GeV gamma rays from the region
surrounding the Galactic Center, consistent with the emission expected from annihilating dark
matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics
and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails
of the point spread function and generate high resolution gamma-ray maps, enabling us to more
easily separate the various gamma-ray components. Within these maps, we find the GeV excess
to be robust and highly statistically significant, with a spectrum, angular distribution, and overall
normalization that is in good agreement with that predicted by simple annihilating dark matter
models. For example, the signal is very well fit by a 36-51 GeV dark matter particle annihilating to
b
¯b with an annihilation cross section of σv = (1−3)×10−26 cm3
/s (normalized to a local dark matter
density of 0.4 GeV/cm3
). Furthermore, we confirm that the angular distribution of the excess is
approximately spherically symmetric and centered around the dynamical center of the Milky Way
(within ∼0.05◦
of Sgr A∗
), showing no sign of elongation along the Galactic Plane. The signal is
observed to extend to at least ' 10◦
from the Galactic Center, disfavoring the possibility that this
emission originates from millisecond pulsars.
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
A magnetar-powered X-ray transient as the aftermath of a binary neutron-star ...Sérgio Sacani
Mergers of neutron stars are known to be associated with short γ-ray
bursts1–4
. If the neutron-star equation of state is sufficiently stiff
(that is, the pressure increases sharply as the density increases), at
least some such mergers will leave behind a supramassive or even a
stable neutron star that spins rapidly with a strong magnetic field5–8
(that is, a magnetar). Such a magnetar signature may have been
observed in the form of the X-ray plateau that follows up to half
of observed short γ-ray bursts9,10. However, it has been expected
that some X-ray transients powered by binary neutron-star mergers
may not be associated with a short γ-ray burst11,12. A fast X-ray
transient (CDF-S XT1) was recently found to be associated with a
faint host galaxy, the redshift of which is unknown13. Its X-ray and
host-galaxy properties allow several possible explanations including
a short γ-ray burst seen off-axis, a low-luminosity γ-ray burst at
high redshift, or a tidal disruption event involving an intermediatemass black hole and a white dwarf13. Here we report a second X-ray
transient, CDF-S XT2, that is associated with a galaxy at redshift
z = 0.738 (ref. 14). The measured light curve is fully consistent with
the X-ray transient being powered by a millisecond magnetar. More
intriguingly, CDF-S XT2 lies in the outskirts of its star-forming host
galaxy with a moderate offset from the galaxy centre, as short γ-ray
bursts often do15,16. The estimated event-rate density of similar
X-ray transients, when corrected to the local value, is consistent
with the event-rate density of binary neutron-star mergers that is
robustly inferred from the detection of the gravitational-wave event
GW170817.
No large population of unbound or wide-orbit Jupiter-mass planets Sérgio Sacani
Planet formation theories predict that some planets may be ejected from their parent systems as result of dynamical interactions and other processes1–3. Unbound planets can also be formed through gravitational collapse, in a way similar to that in which stars form4. A handful of free-floating planetary-mass objects have been discovered by infrared surveys of young stellar clusters and star-forming regions5,6 as well as wide-field surveys7, but these studies are incomplete8–10 for objects below five Jupiter masses. Gravitational microlensing is the only method capable of exploring the entire population of free-floating planets down to Mars-mass objects, because the microlensing signal does not depend on the brightness of the lensing object. A characteristic timescale of microlensing events depends on the mass of the lens: the less massive the lens, the shorter the microlensing event. A previous analysis11 of 474 microlensing events found an excess of ten very short events (1–2 days)—more than known stellar populations would suggest—indicating the existence of a large population of unbound or wide-orbit Jupiter-mass planets (reported to be almost twice as common as main-sequence stars). These results, however, do not match predictions of planet-formation theories3,12 and surveys of young clusters8–10. Here we analyse a sample of microlensing events six times larger than that of ref. 11 discovered during the years 2010–15. Although our survey has very high sensitivity (detection efficiency) to short-timescale (1–2 days) microlensing events, we found no excess of events with timescales in this range, with a
95 per cent upper limit on the frequency of Jupiter-mass freefloating or wide-orbit planets of 0.25 planets per main-sequence star. We detected a few possible ultrashort-timescale events (with timescales of less than half a day), which may indicate the existence of Earth-mass and super-Earth-mass free-floating planets, as predicted by planet-formation theories3,12.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
Forming intracluster gas in a galaxy protocluster at a redshift of 2.16Sérgio Sacani
Galaxy clusters are the most massive gravitationally bound structures in the Universe, comprising thousands of galaxies and
pervaded by a diffuse, hot “intracluster medium” (ICM) that dominates the baryonic content of these systems. The formation
and evolution of the ICM across cosmic time1
is thought to be driven by the continuous accretion of matter from the large-scale
filamentary surroundings and dramatic merger events with other clusters or groups. Until now, however, direct observations of
the intracluster gas have been limited only to mature clusters in the latter three-quarters of the history of the Universe, and we
have been lacking a direct view of the hot, thermalized cluster atmosphere at the epoch when the first massive clusters formed.
Here we report the detection (about 6σ) of the thermal Sunyaev-Zeldovich (SZ) effect2
in the direction of a protocluster. In fact,
the SZ signal reveals the ICM thermal energy in a way that is insensitive to cosmological dimming, making it ideal for tracing
the thermal history of cosmic structures3
. This result indicates the presence of a nascent ICM within the Spiderweb protocluster
at redshift z = 2.156, around 10 billion years ago. The amplitude and morphology of the detected signal show that the SZ
effect from the protocluster is lower than expected from dynamical considerations and comparable with that of lower-redshift
group-scale systems, consistent with expectations for a dynamically active progenitor of a local galaxy cluster.
The Hubble Tension and Early Dark EnergySérgio Sacani
Over the past decade, the disparity between the value of the cosmic
expansion rate directly determined from measurements of distance and
redshift or instead from the standard ΛCDM cosmological model calibrated by measurements from the early Universe, has grown to a level
of significance requiring a solution. Proposed systematic errors are
not supported by the breadth of available data (and “unknown errors”
untestable by lack of definition). Simple theoretical explanations for
this “Hubble tension” that are consistent with the majority of the data
have been surprisingly hard to come by, but in recent years, attention has focused increasingly on models that alter the early or prerecombination physics of ΛCDM as the most feasible. Here, we describe the nature of this tension, emphasizing recent developments on
the observational side. We then explain why early-Universe solutions
are currently favored and the constraints that any such model must satisfy. We discuss one workable example, early dark energy, and describe
how it can be tested with future measurements. Given an assortment
of more extended recent reviews on specific aspects of the problem,
the discussion is intended to be fairly general and understandable to a
broad audience.
The atacama cosmology_telescope_measuring_radio_galaxy_bias_through_cross_cor...Sérgio Sacani
A radiação cósmica de micro-ondas aponta para a matéria escura invisível, marcando o ponto onde jatos de material viajam a velocidades próximas da velocidade da luz, de acordo com uma equipe internacional de astrônomos. O principal autor do estudo, Rupert Allison da Universidade de Oxford apresentou os resultados no dia 6 de Julho de 2015 no National Astronomy Meeting em Venue Cymru, em Llandudno em Wales.
Atualmente, ninguém sabe ao certo do que a matéria escura é feita, mas ela é responsável por cerca de 26% do conteúdo de energia do universo, com galáxias massivas se formando em densas regiões de matéria escura. Embora invisível, a matéria escura se mostra através do efeito gravitacional – uma grande bolha de matéria escura puxa a matéria normal (como elétrons, prótons e nêutrons) através de sua própria gravidade, eventualmente se empacotando conjuntamente para criar as estrelas e galáxias inteiras.
Muitas das maiores dessas são galáxias ativas com buracos negros supermassivos em seus centros. Alguma parte do gás caindo diretamente na direção do buraco negro é ejetada como jatos de partículas e radiação. As observações feitas com rádio telescópios mostram que esses jatos as vezes se espalham por milhões de anos-luz desde a galáxia – mais distante até mesmo do que a extensão da própria galáxia.
Os cientistas esperam que os jatos possam viver em regiões onde existe um excesso de concentração da matéria escura, maior do que o da média. Mas como a matéria escura é invisível, testar essa ideia não é algo tão direto.
3D-Spatiotemporal forecasting the expansion of supernova shells using deep le...Sérgio Sacani
Supernova (SN) plays an important role in galaxy formation and evolution. In high-resolution galaxy simulations using massively
parallel computing, short integration time-steps for SNe are serious bottlenecks. This is an urgent issue that needs to be resolved
for future higher-resolution galaxy simulations. One possible solution would be to use the Hamiltonian splitting method, in
which regions requiring short time-steps are integrated separately from the entire system. To apply this method to the particles
affected by SNe in a smoothed particle hydrodynamics simulation, we need to detect the shape of the shell on and within which
such SN-affected particles reside during the subsequent global step in advance. In this paper, we develop a deep learning model,
3D-Memory In Memory (3D-MIM), to predict a shell expansion after a SN explosion. Trained on turbulent cloud simulations
with particle mass mgas = 1 M, the model accurately reproduces the anisotropic shell shape, where densities decrease by over
10 per cent by the explosion. We also demonstrate that the model properly predicts the shell radius in the uniform medium
beyond the training data set of inhomogeneous turbulent clouds. We conclude that our model enables the forecast of the shell
and its interior where SN-affected particles will be present.
Exploring Proxies for the Supermassive Black Hole Mass Function: Implications...Sérgio Sacani
Supermassive black holes (SMBHs) reside at the center of every massive galaxy in the local universe with masses
that closely correlate with observations of their host galaxy, implying a connected evolutionary history. The
population of binary SMBHs, which form following galaxy mergers, is expected to produce a gravitational-wave
background (GWB) detectable by pulsar timing arrays (PTAs). PTAs are starting to see hints of what may be a
GWB, and the amplitude of the emerging signal is toward the higher end of model predictions. Simulated
populations of binary SMBHs can be constructed from observations of galaxies and are used to make predictions
about the nature of the GWB. The greatest source of uncertainty in these observation-based models comes from the
inference of the SMBH mass function, which is derived from observed host galaxy properties. In this paper, I
undertake a new approach for inferring the SMBH mass function, starting from a velocity dispersion function
rather than a galaxy stellar mass function. I argue that this method allows for a more direct inference by relying on
a larger suite of individual galaxy observations as well as relying on a more “fundamental” SMBH mass relation. I
find that the resulting binary SMBH population contains more massive systems at higher redshifts than previous
models. Additionally, I explore the implications for the detection of individually resolvable sources in PTA data.
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.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
Enchancing adoption of Open Source Libraries. A case study on Albumentations.AIVladimir Iglovikov, Ph.D.
Presented by Vladimir Iglovikov:
- https://www.linkedin.com/in/iglovikov/
- https://x.com/viglovikov
- https://www.instagram.com/ternaus/
This presentation delves into the journey of Albumentations.ai, a highly successful open-source library for data augmentation.
Created out of a necessity for superior performance in Kaggle competitions, Albumentations has grown to become a widely used tool among data scientists and machine learning practitioners.
This case study covers various aspects, including:
People: The contributors and community that have supported Albumentations.
Metrics: The success indicators such as downloads, daily active users, GitHub stars, and financial contributions.
Challenges: The hurdles in monetizing open-source projects and measuring user engagement.
Development Practices: Best practices for creating, maintaining, and scaling open-source libraries, including code hygiene, CI/CD, and fast iteration.
Community Building: Strategies for making adoption easy, iterating quickly, and fostering a vibrant, engaged community.
Marketing: Both online and offline marketing tactics, focusing on real, impactful interactions and collaborations.
Mental Health: Maintaining balance and not feeling pressured by user demands.
Key insights include the importance of automation, making the adoption process seamless, and leveraging offline interactions for marketing. The presentation also emphasizes the need for continuous small improvements and building a friendly, inclusive community that contributes to the project's growth.
Vladimir Iglovikov brings his extensive experience as a Kaggle Grandmaster, ex-Staff ML Engineer at Lyft, sharing valuable lessons and practical advice for anyone looking to enhance the adoption of their open-source projects.
Explore more about Albumentations and join the community at:
GitHub: https://github.com/albumentations-team/albumentations
Website: https://albumentations.ai/
LinkedIn: https://www.linkedin.com/company/100504475
Twitter: https://x.com/albumentations
LF Energy Webinar: Electrical Grid Modelling and Simulation Through PowSyBl -...DanBrown980551
Do you want to learn how to model and simulate an electrical network from scratch in under an hour?
Then welcome to this PowSyBl workshop, hosted by Rte, the French Transmission System Operator (TSO)!
During the webinar, you will discover the PowSyBl ecosystem as well as handle and study an electrical network through an interactive Python notebook.
PowSyBl is an open source project hosted by LF Energy, which offers a comprehensive set of features for electrical grid modelling and simulation. Among other advanced features, PowSyBl provides:
- A fully editable and extendable library for grid component modelling;
- Visualization tools to display your network;
- Grid simulation tools, such as power flows, security analyses (with or without remedial actions) and sensitivity analyses;
The framework is mostly written in Java, with a Python binding so that Python developers can access PowSyBl functionalities as well.
What you will learn during the webinar:
- For beginners: discover PowSyBl's functionalities through a quick general presentation and the notebook, without needing any expert coding skills;
- For advanced developers: master the skills to efficiently apply PowSyBl functionalities to your real-world scenarios.
UiPath Test Automation using UiPath Test Suite series, part 6DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 6. In this session, we will cover Test Automation with generative AI and Open AI.
UiPath Test Automation with generative AI and Open AI webinar offers an in-depth exploration of leveraging cutting-edge technologies for test automation within the UiPath platform. Attendees will delve into the integration of generative AI, a test automation solution, with Open AI advanced natural language processing capabilities.
Throughout the session, participants will discover how this synergy empowers testers to automate repetitive tasks, enhance testing accuracy, and expedite the software testing life cycle. Topics covered include the seamless integration process, practical use cases, and the benefits of harnessing AI-driven automation for UiPath testing initiatives. By attending this webinar, testers, and automation professionals can gain valuable insights into harnessing the power of AI to optimize their test automation workflows within the UiPath ecosystem, ultimately driving efficiency and quality in software development processes.
What will you get from this session?
1. Insights into integrating generative AI.
2. Understanding how this integration enhances test automation within the UiPath platform
3. Practical demonstrations
4. Exploration of real-world use cases illustrating the benefits of AI-driven test automation for UiPath
Topics covered:
What is generative AI
Test Automation with generative AI and Open AI.
UiPath integration with generative AI
Speaker:
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
zkStudyClub - Reef: Fast Succinct Non-Interactive Zero-Knowledge Regex ProofsAlex Pruden
This paper presents Reef, a system for generating publicly verifiable succinct non-interactive zero-knowledge proofs that a committed document matches or does not match a regular expression. We describe applications such as proving the strength of passwords, the provenance of email despite redactions, the validity of oblivious DNS queries, and the existence of mutations in DNA. Reef supports the Perl Compatible Regular Expression syntax, including wildcards, alternation, ranges, capture groups, Kleene star, negations, and lookarounds. Reef introduces a new type of automata, Skipping Alternating Finite Automata (SAFA), that skips irrelevant parts of a document when producing proofs without undermining soundness, and instantiates SAFA with a lookup argument. Our experimental evaluation confirms that Reef can generate proofs for documents with 32M characters; the proofs are small and cheap to verify (under a second).
Paper: https://eprint.iacr.org/2023/1886
Generative AI Deep Dive: Advancing from Proof of Concept to ProductionAggregage
Join Maher Hanafi, VP of Engineering at Betterworks, in this new session where he'll share a practical framework to transform Gen AI prototypes into impactful products! He'll delve into the complexities of data collection and management, model selection and optimization, and ensuring security, scalability, and responsible use.
GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using Deplo...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
Maruthi Prithivirajan, Head of ASEAN & IN Solution Architecture, Neo4j
Get an inside look at the latest Neo4j innovations that enable relationship-driven intelligence at scale. Learn more about the newest cloud integrations and product enhancements that make Neo4j an essential choice for developers building apps with interconnected data and generative AI.
GridMate - End to end testing is a critical piece to ensure quality and avoid...ThomasParaiso2
End to end testing is a critical piece to ensure quality and avoid regressions. In this session, we share our journey building an E2E testing pipeline for GridMate components (LWC and Aura) using Cypress, JSForce, FakerJS…
Dr. Sean Tan, Head of Data Science, Changi Airport Group
Discover how Changi Airport Group (CAG) leverages graph technologies and generative AI to revolutionize their search capabilities. This session delves into the unique search needs of CAG’s diverse passengers and customers, showcasing how graph data structures enhance the accuracy and relevance of AI-generated search results, mitigating the risk of “hallucinations” and improving the overall customer journey.
Encryption in Microsoft 365 - ExpertsLive Netherlands 2024Albert Hoitingh
In this session I delve into the encryption technology used in Microsoft 365 and Microsoft Purview. Including the concepts of Customer Key and Double Key Encryption.
Building RAG with self-deployed Milvus vector database and Snowpark Container...Zilliz
This talk will give hands-on advice on building RAG applications with an open-source Milvus database deployed as a docker container. We will also introduce the integration of Milvus with Snowpark Container Services.
Sudheer Mechineni, Head of Application Frameworks, Standard Chartered Bank
Discover how Standard Chartered Bank harnessed the power of Neo4j to transform complex data access challenges into a dynamic, scalable graph database solution. This keynote will cover their journey from initial adoption to deploying a fully automated, enterprise-grade causal cluster, highlighting key strategies for modelling organisational changes and ensuring robust disaster recovery. Learn how these innovations have not only enhanced Standard Chartered Bank’s data infrastructure but also positioned them as pioneers in the banking sector’s adoption of graph technology.
Elizabeth Buie - Older adults: Are we really designing for our future selves?
The significance of_the_integrated_sachs_wolfe_effect_revisited
1. Mon. Not. R. Astron. Soc. 000, 1–19 (2012) Printed 12 September 2012 (MN L TEX style file v2.2)
A
The significance of the integrated Sachs-Wolfe effect revisited
Tommaso Giannantonio1,2⋆ , Robert Crittenden3 , Robert Nichol3,4, Ashley J. Ross3
1 Ludwig-Maximilians-Universit¨ t M¨ nchen, Universit¨ ts-Sternwarte M¨ nchen, Scheinerstr. 1, D-81679 M¨ nchen, Germany
a u a u u
2 Excellence Cluster Universe, Technical University Munich, Boltzmannstr. 2, D-85748 Garching bei M¨ nchen, Germany
u
3 Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 3FX, UK
arXiv:1209.2125v1 [astro-ph.CO] 10 Sep 2012
4 SEPnet, South East Physics Network
12 September 2012
ABSTRACT
We revisit the state of the integrated Sachs-Wolfe (ISW) effect measurements in light of newly
available data and address criticisms about the measurements which have recently been raised.
We update the data set previously assembled by Giannantonio et al. (2008b) to include new
data releases for both the cosmic microwave background (CMB) and the large-scale structure
(LSS) of the Universe. We find that our updated results are consistent with previous measure-
ments. By fitting a single template amplitude, we now obtain a combined significance of the
ISW detection at the 4.4 σ level, which fluctuates by ∼ 0.4 σ when alternative data cuts and
analysis assumptions are considered. We also make new tests for systematic contaminations
of the data, focusing in particular on the issues raised by Sawangwit et al. (2010). Amongst
them, we address the rotation test, which aims at checking for possible systematics by cor-
relating pairs of randomly rotated maps. We find results consistent with the expected data
covariance, no evidence for enhanced correlation on any preferred axis of rotation, and there-
fore no indication of any additional systematic contamination. We publicly release the results,
the covariance matrix, and the sky maps used to obtain them.
Key words: Cosmic background radiation; Large-scale structure of the Universe; Cosmol-
ogy: observations.
1 INTRODUCTION tection of the ISW represents a measurement of dark energy and
its properties. Unfortunately, the amplitude of the ISW signal is
Observational evidence indicates the expansion of the Universe
small compared with the intrinsic CMB temperature anisotropies,
is accelerating at late times, which may be explained by a small
contributing to the signal only at large scales. To overcome this,
cosmological constant, some negative-pressure dark energy fluid
a technique was introduced to extract the ISW signal by cross-
(Frieman et al. 2008), by modifications of the laws of gravity
correlating the observed CMB with tracers of the local large-scale
(see e.g. Clifton et al. 2012), or by some non-trivial distribution
structure (LSS) of the Universe, such as wide-area galaxy cata-
of the local large-scale structure (see e.g. Dunsby et al. 2010).
logues (Crittenden & Turok 1996). As we will review below, this
Evidence for this acceleration is provided by multiple comple-
method has been used to successfully detect this signature of dark
mentary probes, such as observations of distant Type Ia su-
energy by many authors using several different LSS catalogues and
pernovae (Amanullah et al. 2010; Lampeitl et al. 2010a,b), cos-
the WMAP data of the CMB. More recently, multiple data sets were
mic microwave background (CMB) anisotropies (Komatsu et al.
analysed jointly to maximise the extracted signal (Ho et al. 2008;
2011), baryon acoustic oscillations (BAO) (Eisenstein et al. 2005;
Giannantonio et al. 2008b) (G08 herein), thus detecting the ISW
Percival et al. 2010), clusters of galaxies (Rozo et al. 2010), and the
signal at an overall significance of ∼ 4 σ, when fit a single ampli-
integrated Sachs-Wolfe (ISW) effect (Giannantonio et al. 2008b;
tude.
Ho et al. 2008).
We shall focus here on the latter, which consists of small However, some concerns have been raised about
secondary fluctuations in the CMB which are produced whenever these detections, notably by Sawangwit et al. (2010);
gravitational potentials are evolving, as happens at late times in Francis & Peacock (2010a,b); Hern´ ndez-Monteagudo (2010);
a
the case of the Universe undergoing a transition to a curvature- or L´ pez-Corredoira et al. (2010). These concerns relate to three
o
dark energy-dominated phase (Sachs & Wolfe 1967). If we assume main areas: conflicting estimates of the statistical significance;
a flat universe as supported by the primary CMB data, then a de- searches based on new photometric data sets; and the possibility of
larger than expected systematic contaminations.
The purpose of this paper is twofold. First we update our anal-
⋆ E-mail: tommaso.giannantonio at usm.lmu.de ysis to include the latest data of both the CMB and the large-scale
c 2012 RAS
2. 2 T. Giannantonio, R. Crittenden, R. Nichol and A. J. Ross
structure, using the 7-year WMAP maps and the latest available re- 2.1.1 Cross-correlations
leases of the Sloan Digital Sky Survey (SDSS); we also publicly
Despite the small amplitude of the late ISW anisotropies, they can
release the results of our analysis and our sky maps. Second, we
be used to constrain dark energy, as their presence can be detected
evaluate the above-mentioned criticism and re-assess the overall
by cross-correlating the observed CMB with the local matter den-
state of the ISW measurements, focusing in particular on address-
sity, which traces the gravitational potential (Crittenden & Turok
ing the concerns by Sawangwit et al. (2010) (S10 herein).
ˆ
1996). The CMB temperature anisotropy ΘISW (n) is given by
The plan of the paper is as follows: after reviewing the anal-
ˆ
Eq. (1), and the galaxy density contrast δg (n) can be calculated as
ysis techniques and the current state of the ISW measurements in
Section 2, we will describe our updated data set and the publicly
ˆ
δg (n) = ˆ ˆ
bg (n, z) ϕ(z) δ(n, z) dz , (2)
released maps in Section 3. We then move on to a discussion of
systematic uncertainties in Section 4, where we address a partic-
ˆ
where δ(n, z) is the dark matter density perturbation (linear theory
ular type of systematic test which has been discussed in S10 (the
suffices as described above), bg the (linear) galactic bias and ϕ(z) is
rotation test), finding results consistent with those expected given
the normalised visibility function of the chosen galaxy survey. This
the covariance of the data. Further issues raised by S10 and other
enables us to calculate the cross power spectrum,
authors are addressed in Section 5, before we conclude in Section
6. 2
ClT g, ISW = dk k2 P(k) WlT, ISW (k) Wlg (k) , (3)
π
where P(k) is the matter power spectrum (linear theory suffices as
well), and the source terms are, if we consider only the ISW tem-
perature anisotropies,
2 THE STATE OF THE ISW d ˜
WlT, ISW (k) = − dz e−τ(z) ˜
Φ(k, z) + Ψ(k, z) jl [kχ(z)]
2.1 Theory dz
The ISW effect (Sachs & Wolfe 1967) is a secondary source of Wlg (k) = ˜ ˜
dz bg (k, z) ϕ(z) δ(k, z) jl [kχ(z)] , (4)
temperature anisotropy which is produced whenever the gravita-
tional potentials Φ and Ψ are evolving in time, generating temper- where the tilde denotes Fourier transformation and the jl are the
ature anisotropies of the form spherical Bessel functions. The auto-power spectra for the galax-
ies Clgg and the CMB (either the ISW part only ClT T, ISW or the
ˆ
ΘISW (n) = − ˙ ˙
e−τ(z) Φ + Ψ [η, n(η0 − η)] dη ,
ˆ (1) full observable spectrum ClT T, tot ) can also be calculated by using
the relevant source terms accordingly. In this work we calculate all
the theoretical predictions implementing the above equations into a
where η is conformal time, the dots represent conformal-time
modified version of the CAMB integrator code (Lewis et al. 2000),
derivatives, τ is the optical depth, and e−τ(z) is the CMB photon
without using the Limber approximation.
visibility function. In the best-fit cosmological model, consisting
Notice that in the ΛCDM model and in most of its vari-
of cold dark matter and a cosmological constant (ΛCDM), such
ants, as long as secondary Doppler effects due to reionisation can
anisotropies are generated at early times during the transition from
be neglected (Giannantonio & Crittenden 2007), the only signifi-
radiation to matter domination and at late times, when dark energy
cant source of large-angle CMB-density correlation is the ISW ef-
begins to dominate, so these two contributions are known as the
fect: we will therefore use the simpler notation ClT g for the cross-
early and late ISW effects.
correlations.
The early effect is typically generated shortly after recombi-
nation, so it is peaked around l ∼ 100, and its contribution to the
total CMB (which is small in the standard ΛCDM case) can be
used to constrain the energy content of relativistic species, such as
the number of neutrino species and their masses (Ichikawa et al. 2.1.2 Signal-to-noise
2008), the presence of hot-dark-matter candidates such as massive
neutrinos and axions (Hannestad et al. 2010), and interacting dark The maximum signal-to-noise (S /N) ratio which is achievable for
energy models (V¨ liviita et al. 2010).
a the ISW is limited by the amplitude of the primordial CMB pertur-
We focus here on the late effect as a probe of dark energy; bations. For an idealised full-sky full-depth survey, one can write
in this case, the amplitude of the perturbations is also small com- (Crittenden & Turok 1996)
pared with the primary CMB, and the fluctuations are generated on
S 2 ClT T, ISW
the largest scales, meaning that the effect is well described by lin- ≤ (2l + 1) · ; (5)
ear theory. However, there is a small additional contribution from N l ClT T, tot
the non-linear growth in clusters, known as the Rees-Sciama ef- for the current WMAP7 ΛCDM model (Komatsu et al. 2011) de-
fect (Rees & Sciama 1968). For a review, see Cooray (2002); in scribed below in Section 3, this limit amounts to S /N < 7.6, as
more recent work, Smith et al. (2009) provide a comparison with shown in Fig. 1. A more realistic estimation which takes into ac-
N-body simulations and perturbation theory, and Cai et al. (2010) count the limitations of a galaxy survey, such as its redshift distri-
give a comparison of linear and non-linear effects on the recon- bution, its shot noise due to finite surface density ns (in sr−1 ) and its
structed ISW maps from ray tracing of CMB photons through N- sky coverage fsky , is given by (see e.g. G08; Cabr´ et al. 2007):
e
body simulations. Finally, Sch¨ fer et al. (2011) quantify the param-
a
2
eter estimation bias due to this non-linear effect and show that it is 2 ClT g
S
small compared to the statistical uncertainty imparted by cosmic ≃ fsky (2l + 1) · 2
. (6)
variance. N l ClT g + ClT T, tot Clgg + 1/ns
c 2012 RAS, MNRAS 000, 1–19
3. The significance of the integrated Sachs-Wolfe effect revisited 3
tions or cross power spectra. While these approaches are formally
equivalent, in practice some small differences can arise.
2.2.1 Cross-correlation functions
In real space, the observable quantity is the cross-correlation func-
tion (CCF) between CMB temperature and galaxies defined as
wT g (ϑ) ≡ Θ(n1 ) δg (n2 ) ,
ˆ ˆ (7)
where the average is carried out over all the pairs of directions in
ˆ ˆ
the sky lying at the given angular separation ϑ = |n1 − n2 |. This
approach has the advantage of being computationally straightfor-
ward, since the sky masks are defined in real space and are easily
treated; the main drawback is the high level of covariance between
the measured data points.
Following the release of the WMAP data, several groups
reported positive detections using a wide range of LSS cata-
logues: the first measurement by Boughn & Crittenden (2004)
used a combination of NVSS radio galaxies and X-ray back-
ground data, and the NVSS result was independently confirmed
by Nolta et al. (2004). For optical surveys, indications were seen
by Fosalba & Gazta˜ aga (2004) using the APM survey, and the ev-
n
idence was improved by Fosalba et al. (2003) and Scranton et al.
(2003) by using Luminous Red Galaxies (LRGs) from the SDSS.
Cabr´ et al. (2006) detected the effect using the main SDSS
e
galaxy sample, which while shallower, contains more galaxies
than the LRG sample; Rassat et al. (2007) re-examined the rela-
tively shallow 2MASS infrared survey, which was originally anal-
ysed with the power spectrum method by Afshordi et al. (2004). In
Giannantonio et al. (2006), we reported the highest-redshift detec-
tion of the ISW with a catalogue of quasars from the SDSS, which
was later reanalysed by Xia et al. (2009).
Most of these papers report a positive detection at low signif-
Figure 1. Theoretical spectra and maximum signal-to-noise of the ISW icance, typically between 2 and 3 σ. One exception is the analysis
detection for the current WMAP7 best-fit model (Komatsu et al. 2011).
using the 2MASS data where, though it favours the expected ISW
The top panel shows the angular temperature power spectrum of the ISW
signal, the evidence is very weak because the sample is too shallow
(green, solid) compared with the total CMB (red, dashed) and the data from
WMAP7 (blue) (Larson et al. 2011). The bottom panel shows the maximum for an appreciable ISW signal; it also is believed to have significant
signal-to-noise (per mode and cumulative) achievable given the same model contamination from the Sunyaev-Zel’dovich (SZ) effect.
as given by Eq. (5) (brown, dot-dashed), as well as the improvement using
CMB polarisation given by Eq. (8) (blue, solid).
2.2.2 Cross-power spectra
We can also attempt to measure the angular power spectra of the
Applying this expression to detections coming from current single
cross-correlation directly. The main advantage of this approach is
galaxy catalogues typically yields only moderate significance (2
the relative decorrelation of the different modes, which makes the
S /N 3).
localisation of the signal on different scales more straightforward;
Early attempts were made to measure the two-point cor-
the drawback is that the estimator of the correlation involves the
relation between COBE CMB data and tracers of the LSS
inversion of a matrix whose dimensionality is the number of pixels
(Boughn & Crittenden 2002), but these were limited by the noise
over which the maps are projected (Npix ), which is computationally
and resolution of the COBE data. However, the ISW effect
challenging, especially in realistic cases where the geometry of the
was soon detected using the WMAP data by many different
survey mask is complex. For these reasons, approximate methods
groups exploiting a range of techniques; the first detection by
are generally used (for details, see e.g. Padmanabhan et al. 2003;
Boughn & Crittenden (2004) used the X-ray background from the
Efstathiou 2004; Hirata et al. 2004; Ho et al. 2008; Schiavon et al.
HEAO satellite and radio-galaxies from the NVSS survey, and was
2012), which still yield considerably lower correlation between
followed quickly by many others as we review below.
modes when compared to cross-correlation measurements.
In this way, positive detections were reported by
Afshordi et al. (2004) using the 2MASS catalogue, who si-
2.2 Single catalogue measurements
multaneously fit a template for the SZ effect; this was recently
The first ISW analyses were focused on detection at any signifi- revisited by Francis & Peacock (2010b) who found weaker evi-
cance, measuring the two-point correlations of the WMAP CMB dence more consistent with Rassat et al. (2007) and other analyses.
data and galaxy catalogues. This analysis can be performed equiv- Padmanabhan et al. (2005) applied the cross-spectrum technique
alently in the real or harmonic spaces, using cross-correlation func- to a SDSS LRG sample, and found consistent significance levels
c 2012 RAS, MNRAS 000, 1–19
4. 4 T. Giannantonio, R. Crittenden, R. Nichol and A. J. Ross
to the earlier work, at about 2 σ. More recently, Goto et al. (2012) find that this improves the upper limit to S /N < 8.7, as shown in
measured the correlation between WMAP and the Wide-field Fig. 1.
Infrared Survey Explorer (WISE) survey, finding a high ISW Most of the approaches effectively measure a two-point statis-
signal at > 3 σ. While the WISE volume is ∼ 5 times larger tic of the average correlations between CMB and LSS over the
than 2MASS, and thus the expected signal is higher, such a high whole region covered by the surveys; however, with wavelets it
correlation is ∼ 2.2 σ higher than the ΛCDM expectations. Future is possible to try to localise sources of the ISW effect. This was
analyses with the upcoming larger WISE data releases will help to more directly attempted by Granett et al. (2008), who identified
clarify this issue. massive superclusters and voids of galaxies in the SDSS LRG sur-
Given accurate covariance matrices, cross-correlation and vey and their corresponding regions from WMAP were stacked to
cross-spectra measurements (using the same data), should yield maximise the signal. A high significance detection was reported
identical results, as, in total, both measurements contain the same (at 4.4 σ from this LRG catalogue alone), although this result was
information. strongly dependent on the number of superclusters and voids used.
See below Section 5.1.6 for a more detailed discussion.
2.2.3 Other techniques
2.3 Multiple catalogues measurements and their applications
The ISW effect has also been seen using a method based on
The significance of the ISW detections can be increased by combin-
a wavelet decomposition by Vielva et al. (2006); McEwen et al.
ing measurements obtained with multiple catalogues, to improve
(2007, 2008); Pietrobon et al. (2006), who explored its dependence
from a simple detection to parameter estimation and model com-
on different wavelet shapes and scales. While the significance level
parison. Gazta˜ aga et al. (2006) made a first attempt at collecting
n
was sometimes reported to have been enhanced with this technique,
all the existing measurements and used the resulting compilation
the resulting constraints on cosmology were comparable with the
to constrain cosmology; this was also extended by Corasaniti et al.
previous two methods.
(2005).
As the ISW is maximum on the largest scales, it is affected
The difficulty with combining multiple measurements is
by the local variance, i.e. by the particular realisation of the mat-
achieving a reliable estimation of the covariance between them. It
ter distribution given the power spectrum; this may bias the results.
was proposed that a full tomographic analysis should be performed
For this reason, more advanced methods were developed to sub-
(Pogosian et al. 2005), including all the signals, and their covari-
tract the local variance, e.g. by Hern´ ndez-Monteagudo (2008);
a
ances, as a function of redshift. This was finally achieved inde-
Frommert et al. (2008). In the latter work, a Wiener filter recon-
pendently by Ho et al. (2008), using the harmonic space estimator,
struction of the LSS was used as a template instead of the theo-
and by Giannantonio et al. (2008b) in real space, using five1 and
retical cross-correlation function; it was estimated that this method
six galaxy catalogues respectively, summarising the state of the art
may increase the S/N ratio by 7% in average.
in the field and upgrading the significance to 3.7 σ and 4.5 σ re-
It is also possible to reconstruct the ISW temperature maps. spectively. These results have been used to test a variety of dark
This was attempted by Barreiro et al. (2008) using NVSS data and energy and modified gravity models (Giannantonio et al. 2008a;
a Wiener filter method, and by Granett et al. (2009) using SDSS Giannantonio et al. 2010; Lombriser et al. 2009; Lombriser et al.
data (see Section 5.1.6). Another optimised method has been later 2012; Lombriser 2011; V¨ liviita & Giannantonio 2009; Serra et al.
a
introduced by Dup´ et al. (2011), based on the analysis of the tem-
e 2009; Daniel et al. 2009; Zhao et al. 2010; Bertacca et al. 2011); in
perature and density fields themselves rather than their spectra. A the modified gravity case, the ISW provides a particularly useful
useful byproduct of this procedure is that a map of the ISW sig- constraint because it is sensitive to any non-trivial evolution of the
nal in the CMB is obtained. These authors also highlight the im- gravitational potentials and the effective anisotropic stress.
portance of separating the different statistical analyses, defining
different procedures for testing the detection of a correlation in a
model-independent way, measuring the confidence level based on
2.4 Potential issues
a template, and comparing different models. This method was then
validated with the 2MASS data, recovering a weak positive detec- Alongside these developments, some studies have questioned in-
tion. dividual aspects of the ISW measurements, raising some doubts
Another strategy to improve the signal-to-noise is to about the significance of its detection.
use the CMB polarisation information to reduce the pri- In Francis & Peacock (2010a,b), the 2MASS-CMB cross-
mary CMB anisotropies, as proposed by Crittenden (2006); correlation was re-analysed, and it was found that there is little
Frommert & Enßlin (2009); Liu et al. (2011). Depending on the de- evidence for an ISW detection from this catalogue alone, which is
tails of the method, different authors estimate a level of improve- in agreement with most previous literature. But more worryingly,
ment in the significance of the ISW detection in the range between 5 these authors also state that the ISW signal may remain undetected
and 20%. In more detail, the correlation ClT E between CMB temper- in 10% of cases (see Section 5.1.3 below).
ature and polarisation (E-modes) can be used to reduce the amount In Hern´ ndez-Monteagudo (2010), the NVSS catalogue was
a
of primary anisotropies in the total temperature spectrum. Assum- re-considered, looking at its auto- and cross-correlation functions
ing idealised data, the maximum signal-to-noise of Eq. (5) is thus in both real and harmonic spaces. In both cases, some cross-
increased to correlation was seen, but the paper expressed concerns regarding
a lower than expected signal on the largest scales and anomalous
S 2 ClT T, ISW
≤ (2l + 1) · 2
. (8)
N l ClT T, tot − ClT E ClEE
1 In the analysis by Ho et al. (2008) some of the catalogues where subdi-
For the current WMAP7 ΛCDM model (Komatsu et al. 2011), we vided further into sub-samples.
c 2012 RAS, MNRAS 000, 1–19
5. The significance of the integrated Sachs-Wolfe effect revisited 5
large-scale structure in the NVSS map. We discuss these issues in public data release (Aihara et al. 2011). These galaxies have been
Section 5.1.5. selected using the same criteria as in G08, i.e. starting from the
Sawangwit et al. (2010) reanalysed some of the earlier ISW photo-z primary galaxy sample (mode=1, type=3), which con-
measurements and extended the analysis with three new LRG data tains 208 million objects, and then imposing a cut in redshift of
sets, including a high-redshift sample developed using AAOmega 0.1 < z < 0.9 and a cut in flux of 18 < r < 21, where r is the r-band
spectra. The two catalogues at lower z were found to be in general model magnitude corrected for extinction. Also, only objects with
agreement with a positive ISW signal, although at lower signifi- photo-z uncertainty of σz (z) < 0.5 z were considered. This leaves
cance than seen elsewhere in the literature, while the high-redshift us with ∼ 40 million galaxies, with a redshift distribution centred
AAOmega sample showed no significant correlation. These authors around z ≃ 0.3. As the distribution of the photo-z’s can occasion-
also discussed the effect of possible systematics, suggesting that ally be inaccurate, for the calculation of the theoretical predictions
there is evidence of strong residual systematics from the study of we used a fit to a distribution function of the form introduced by
data generated by rotating the real maps. We explore the rotation Smail et al. (1994) and given by
tests for our data and for the S10 data in Section 4.2; we then dis- β
cuss the new data sets by S10 in Section 5.2. 1 zα z
ϕ(z) = β α+1 exp − , (9)
Γ α+1 z0 z0
Finally, L´ pez-Corredoira et al. (2010) reviewed some of the
o β
correlation analyses, finding levels of signal comparable to previ-
ous measurements, but significantly higher levels of uncertainty. where the best-fit values of the parameters are α = 1.5, β = 2.3,
We discuss this further in Section 5.1.4. z0 = 0.34; this fitted redshift distribution is similar to the DR6 re-
sult.
The mask was derived from a higher number density sample of
the SDSS galaxies, selected with the weaker conditions r < 22 and
3 UPDATED DATA SET ∆z < z (120 million objects), which was pixellated at a higher reso-
We have updated our data compilation from G08 to include the lution (Nside = 512) and finding the number of filled high-resolution
latest available data for both the CMB and the LSS. All the data sub-pixels in each low-resolution pixel. Each low-resolution pixel
sets are pixellated in the Healpix scheme (Gorski et al. 2005) at was then assigned a weight fig proportional to the fraction of high-
a resolution of Nside = 64, corresponding to a pixel side of 0.9 resolution pixels which were filled.
degrees, as previously done in G08. We have checked that higher An additional subtlety here is to avoid biasing the mask due
resolutions give consistent results. to the high-resolution pixels which are on the edge of the survey
In the following analysis, unless otherwise stated, we assume themselves. We have found that the count-in-cells distribution of
a fiducial flat ΛCDM cosmology, which we here update to the lat- the 120 million galaxies in the high-resolution pixels is well ap-
est best-fit model from WMAP7+BAO+H0 , defined by energy den- proximated by a log-normal distribution of median µ = ln(110),
sities for baryons ωb = 0.0226, cold dark matter ωc = 0.1123, and is even better fit by the gravitational quasi-equilibrium distri-
sound horizon at the last-scattering surface 100 ϑ∗ = 1.0389, op- bution (GQED), described by Yang & Saslaw (2011). By compar-
tical depth τ = 0.087, spectral index and amplitude of primor- ing the best-fitting GQED distribution with the data, we found that
dial scalar perturbations ns = 0.963, A s = 3.195, referred to a the survey’s edges introduce an enhanced tail in the distribution at
pivot scale kpivot = 0.002 h/Mpc (Larson et al. 2011; Komatsu et al. low occupation number which leads to a bias in the mask. For this
2011). reason, we remove from the mask all high-resolution pixels with
We summarise in Table 1 the most important properties of the n < 40, since the best-fit GQED is nearly zero below this point. We
data sets we use. found that our results are not overly sensitive to reasonable differ-
ences in the value chosen for this threshold.
We then mask the sky areas most affected by galactic extinc-
3.1 CMB data tion, dropping all pixels where the median extinction in the r band
The original data set by G08 was obtained by analysing the maps is Ar > 0.18. We have found that increasing this cut to the stricter
from the third year of WMAP, and it was checked upon the re- level of Ar > 0.16 only changes the observed CCF by 5%. The
lease of the WMAP five-year data that it yielded consistent re- unmasked survey area increased from 7,771 pixels (or 16% of the
sults, as mentioned in Section IV.B of G08. Here we have updated sky) for DR6 to 11,715 (or 24 %) for DR8. The DR8 is the first data
the whole analysis by using the latest WMAP7 data (Jarosik et al. release to include a significant fraction of data from the Southern
2011), which should give a more stable foreground subtraction and galactic hemisphere. We have checked that no significant differ-
noise reduction due to the increased integration time. ence appears when excluding data from the Southern hemisphere:
As for the choice of frequency, we use the internal linear com- the differences in the observed CCF are at the 10% level.
bination (ILC) map and we also use the most aggressive galaxy We estimated the galactic bias by fitting the ΛCDM prediction
mask associated with it, again on the basis that this should include to the observed auto-correlation function (ACF), and found a value
the best foreground subtraction. We have checked that the signal b = 1.2 assuming a scale- and redshift-independent bias.
does not change significantly between the different WMAP data
releases, and that it is reasonably frequency-independent and close
to the ILC result in the range of the WMAP bands Q, V, W. We 3.3 Luminous Red Galaxies
discuss this further below. We update the catalogue to include the latest data release of the
MegaZ LRGs by Thomas et al. (2011b), which corresponds to the
SDSS DR7, increasing our previous DR6 coverage by 10%. We ap-
3.2 Main SDSS galaxy data
ply the completeness cut in the de-reddened deVacouleurs i mag-
The main galaxy distribution from the SDSS has been extended nitude suggested by the authors (ideV − Ai < 19.8) and we limit
from Data Release Six (DR6) to the final imaging SDSS-III (DR8) the star-galaxy separation parameter to δ sg > 0.2. We finally ap-
c 2012 RAS, MNRAS 000, 1–19
6. 6 T. Giannantonio, R. Crittenden, R. Nichol and A. J. Ross
Catalogue band N after masking fsky ns [sr−1 ] z
¯ b
2MASS IR 415,459 0.531 6.23 · 104 0.086 1.3
SDSS gal DR8 Optical 30,582,800 0.253 9.60 · 106 0.31 1.2
SDSS LRG DR7 Optical 918,731 0.181 4.03 · 105 0.50 1.7
NVSS Radio 1,021,362 0.474 1.72 · 105 1.05 1.8
HEAO X N/A (flux) 0.275 N/A (flux) 0.90 1.0
SDSS QSO DR6 Optical 502,565 0.168 2.39 · 105 1.51 2.6
Table 1. Summary of the properties of the LSS catalogues used. We report the number of objects after masking N, the sky fraction fsky , the surface density
of sources ns , the median redshift of their distributions z and the galactic bias b assumed constant needed to fit the auto-correlation function assuming the
¯
WMAP7 cosmology.
ply the reddening mask and discard pixels of median extinction at distribution can affect the cross-correlation template, and so im-
Ar > 0.18 as in the main galaxy case. As above, increasing this cut pact the detection significance, and will also change the predicted
to the stricter level of Ar > 0.16 only changes the observed CCF by ΛCDM cosmology amplitudes. Here we have compared the cor-
5%. The redshift distribution in this case peaks around z = 0.5 and relation functions obtained using the distribution function based
is smooth, and we use it directly as done in G08. The mask for the on the models of Dunlop & Peacock (1990) (used in G08), to the
LRGs is that provided by Thomas et al. (2011b), with the addition distribution from De Zotti et al. (2010), who fitted the template
of the aforementioned extinction mask. The bias of this catalogue based on radio galaxies with measured redshifts, and the distribu-
is found to be b = 1.7, again by fitting to the measured ACF. tion function introduced by Ho et al. (2008)2 , who simultaneously
fit the cross-correlation functions between NVSS and other galaxy
catalogues. As seen in Fig. 2, the theoretical predictions for these
3.4 QSO data models are compatible within the expected measurement error bars.
We find that the resulting significance of the NVSS ISW detec-
For the quasars, no updated catalogue is yet publicly available, and tion changes at most by 10% when using each of the three models
here we use the same DR6 catalogue (Richards et al. 2009) as in for the source distribution. In the following, we use the model by
G08, limiting ourselves to the cleaner subset of UV X-selected ob- De Zotti et al. (2010), as it is based on a subsample of galaxies of
jects. To reduce the stellar contamination, which is more of an issue known redshifts. Further, we have included a better modelling of
for quasars, we choose here a stricter extinction cut discarding pix- the shot noise in the ACF, due to the fact the maps were originally
els of Ar > 0.14. Increasing this cut to the stricter level of Ar > 0.12 pixellated at a lower resolution. This primarily affects the ACF, and
changes the observed CCF by less than 10%. so the measurement of the bias; we now find b = 1.8, increased
In this paper we used Eq. (9) to determine a fit to the QSO from b = 1.5 previously assumed in G08.
redshift distribution, for the same reasons described in Section 3.2, For the HEAO catalogue, we have also included the same
and obtained best-fit parameters of α = 2.0, β = 1.5, z0 = 1.06, cor- pixellation correction in the shot noise modelling, but as the instru-
responding to a median z = 1.5. This is changed from G08 where
¯ mental beam is much larger (ϑFWHM = 3.04 degrees), the resulting
the visibility function was simply binned, and not smoothed, and bias parameter remains b = 1.0.
so included irregular steps between adjacent bins.
The linear bias parameter found from the QSO ACF is b = 2.6,
10% higher than that reported in G08. The amount of stellar con- 3.6 Method
tamination, as seen by comparing the large-scale power in the ACF
with the ACF of a catalogue of stars from the SDSS, is consis- We pixellate all these data on the sphere as described above, and
tent with a fraction κ = 2%, which is expected in these data measure the two-point functions between them and the CMB, using
(Richards et al. 2009). the simple estimator
Npix
1 (ni − n)
¯
wT g (ϑ) =
ˆ T j − T fig f jT ,
¯ (10)
Nϑ i, j
n
¯
3.5 Other data where ni and T i are the number of galaxies and the CMB temper-
ature in a pixel of masked weights fig , f jT respectively, n, T are the
¯ ¯
For the other surveys (2MASS, HEAO, and NVSS), we continue average number of galaxies per pixel and average temperature, and
using the same maps as in the previous analysis of G08. However, Nϑ = i, j fig f jT is the weighted number of pairs at a given sepa-
we have improved the analysis in the following ways: ration. Note that in our approach the CMB weights f jT are simply
For the low redshifts probed by 2MASS, non-linear effects are taken to be either 0 or 1, depending on whether the pixel is masked
large enough to significantly affect the zero-lag bin of the ACF; this or unmasked. When fig < 1, which occurs mostly at the edges of
was seen by comparing the linear power spectrum with the result the surveyed area, the number of galaxies in a pixel ni needs to be
obtained by Smith et al. (2007) at the scale of one degree. We have rescaled from the observed number nobs as ni = nobs / fig , in order to
i i
therefore dropped this bin which is significantly higher than the
linear theory prediction, so that the linear bias has decreased to
b = 1.3 in this case. 2 Note the typo in Eq. (33) of Ho et al. (2008), where the argument of the
For NVSS, a well-known issue is the uncertainty in the red- Gamma function should be (α + 1) to ensure the stated normalisation of
shift distribution of the sources. Significant changes to the redshift f (z)dz = beff .
c 2012 RAS, MNRAS 000, 1–19
7. The significance of the integrated Sachs-Wolfe effect revisited 7
the expected correlations between the catalogues. We also add the
expected level of Poisson noise based on the surface densities of
each catalogue on top of all realisation of the Gaussian maps. For
each of 5000 realisations of these maps, we measure the correla-
tion functions, and calculate the covariance of them. (See the Ap-
pendix of G08 for more details.) We have confirmed that 5000 re-
alisations are enough for convergence of the signal-to-noise. As the
cross-correlations are in agreement with the fiducial ΛCDM cos-
mology used in the mocks, we expect this modelling of the covari-
ance should be reasonably accurate. See below Section 5.1.1 for
more details and a comparison with the analytic covariance. Most
catalogues are significantly covariant; the samples which are less
covariant with the others are the LRGs and the QSOs, because of
their unique redshift coverage, which is more peaked in the former
case, and deeper in the latter.
We fit the amplitudes assuming the cross-correlation functions
are Gaussianly distributed; this is approximate, as even if the maps
themselves are Gaussian, as assumed in our Monte Carlos, two
point statistics of those maps will not be Gaussian. However, this
appears to be a reasonable approximation for correlation functions
(and particularly cross-correlations), where each bin represents an
average of many products of pixels and the central limit theorem
should apply. This is confirmed in our Monte Carlos, where we
find the skewness in the covariance to be relatively small, with di-
mensionless skewness measure of 0.1 − 0.2. However, it may be
worth further investigating any residual bias which this level of
non-Gaussianity might cause in future work. Non-Gaussianity is
likely to be a more significant concern for power spectrum estima-
tors, particularly for auto-spectrum measurements which must be
positive-definite.
3.7 Results and public release
The results of the new cross-correlation analysis are shown in
Fig. 3, and are in general agreement with G08 given the measure-
ment errors. We can see that all the measurements lie close to the
ΛCDM prediction; however the LRGs do show an excess signal at
the > 1 σ level. See Section 4 for a discussion of possible system-
atic effects.
The only CCFs for which we see a non-negligible change in
Fig. 3 compared to the earlier analysis by G08 are the LRGs and
the NVSS, where the signal has somewhat increased. This appears
Figure 2. The redshift distribution of NVSS and its effect on the ISW corre- to be primarily due to changes in the WMAP data rather than in the
lation. In the top panel we show three normalised selection functions which
LSS surveys; in Fig. 4 we show the CCFs resulting when the cur-
have been used widely in the literature, and in the bottom panel the result-
ing theoretical cross-correlation functions, compared with our data, for the
rent LSS maps are correlated with different WMAP data releases.
fiducial ΛCDM model. The bias is constant, and set to b = 1.8 for the first With the exception of the LRGs, the changes tend to bring the data
two models as this gives good agreement with the ACF. It is b = 1.98 for into better agreement with the ΛCDM theory. We have found that
the last model, as fitted by Ho et al. (2008). We can see that the differences similar changes appear if the single-frequency, cleaner maps (V and
are small compared with the measurement error bars. We use the model by W) are used instead of the ILC. Further, we found that a significant
De Zotti et al. (2010) in the main analysis. part of these changes is induced by the change in the WMAP mask
between the different releases rather than the change in the data
themselves, suggesting that the differences may be due to a better
foreground cleaning.
keep the same mean density n over the whole map. As in G08, we
¯
use 13 angular bins linearly spaced between 0 and 12 degrees.
We estimate the full covariance matrix C using the ‘MC2’
Monte Carlo method described in G08; specifically, based on the To provide a global estimate of the combined significance, we
fiducial flat ΛCDM cosmology, we generate Gaussian random use a theory template wT g (ϑi ) = Ag(ϑi ), where g(ϑi ) ≡ gi is the
¯
maps of the CMB and of all the galaxy catalogues, using their theoretical prediction of the WMAP7 best fit model and A is the fit
known redshift distributions, number densities, and including all amplitude for each catalogue; further details can be found in G08.
c 2012 RAS, MNRAS 000, 1–19
8. 8 T. Giannantonio, R. Crittenden, R. Nichol and A. J. Ross
Figure 3. Updated results of the cross-correlation of all the data sets with the WMAP7 ILC map. Most data (dark green, solid) are in good agreement with the
theoretical predictions for a ΛCDM model (red, short-dashed), with the only exception of the LRGs which show an excess at >1-σ level. The highly correlated
error bars are from 5000 Monte Carlo mocks and are 1-σ, except for 2MASS where they are 0.5-σ to improve readability of the plot. Further, the first five data
points for 2MASS have been excluded due to potential contamination by the SZ effect. The light-green, long-dashed lines show the previously published data
by G08, and the blue, dot-dashed lines are the best amplitude fits.
By analytically maximising the likelihood, we obtain that the best
value A and its variance for each catalogue are:
p −1
ˆ Tg
−1
p
i, j=1 Ci j gi w j
σ2 = C−1 gi g j , (11)
A= ,
p A ij
−1
i, j=1 Ci j gi g j
i, j=1
where wT g are the observed CCF for each survey (sampled in
ˆi
p = 13 angular bins) and Ci j is the measured covariance matrix of
dimension p described above. To obtain an unbiased estimator of
the inverse covariance C−1 , we correct the result obtained by invert-
ij
ing Ci j by a factor α = (N − p − 2)/(N − 1) (Hartlap et al. 2007);
however in our case (for N = 5000 realisations) this correction
is negligibly small. This method can be immediately generalised
to the full case, in which we fit a single amplitude to a template
which includes the six CCFs. In this case the total number of angu-
lar bins, and thus the dimension of the covariance matrix, becomes
p = 6 × 13 = 78.
The results with this method and the new data are given in
Figure 4. Dependence of the results on the different WMAP data releases.
Most results vary little compared with the size of the error bars; the largest
Table 2, where we can see that if we identify the signal-to-noise
changes can be seen in NVSS, bringing the results closer to the ΛCDM ex- ratio as S /N = A/σA , then the total significance of a detection is
pectations. The error bars on 2MASS are again 0.5-σ. now at the 4.4 σ level when a single amplitude is used for all six
catalogues.
c 2012 RAS, MNRAS 000, 1–19
9. The significance of the integrated Sachs-Wolfe effect revisited 9
Catalogue A ± σA S /N expected S /N
2MASS cut 1.40 ± 2.09 0.7 0.5
SDSS gal DR8 1.24 ± 0.57 2.2 1.6
SDSS LRG DR7 2.10 ± 0.84 2.5 1.2
NVSS 1.21 ± 0.43 2.8 2.6
HEAO 1.37 ± 0.56 2.4 2.0
SDSS QSO DR6 1.43 ± 0.62 2.3 1.7
TOTAL 1.38 ± 0.32 4.4 ± 0.4 ≃ 3.1, < 7.6
Table 2. Results from the updated data set compared with the expected
signal-to-noise calculated using Eq. (6) for each catalogue. The first five
data points for 2MASS have been excluded. For the total expected S /N, we
show both the value estimated from the MC mocks (see below), and using
the upper limit of Eq. (5). We estimate a ∼ 0.4 σ systematic error on the
total signal-to-noise ratio, due to possible different masks and other choices
entering into its determination.
It is worth noticing that our significance estimation is however
based on a fiducial model which includes not only the WMAP7
best-fit parameters, but also the assumed redshift distributions and
simple bias model of the surveys. While this is reasonable to give
an initial estimate of the significance of the detection, a full cosmo-
logical analysis should ideally take into account the uncertainties
in these quantities, e.g. with the help of additional nuisance param-
eters. The assumption of constant biases is especially uncertain, in
particular for very deep catalogues like HEAO and NVSS (see e.g.
Sch¨ fer et al. 2009), and this issue should be addressed in a full
a
cosmological analysis allowing for a more realistic bias evolution.
The different assumptions for the biases and for the redshift distri-
butions may for example explain the difference between our results
and those by Ho et al. (2008), where a higher excess signal was
found, at the 2 σ level above the ΛCDM predictions.
In Table 2 we also compare the results with the expected
signal-to-noise calculated using Eq. (6) for each catalogue, and us-
ing the upper limit of Eq. (5) for the total. We can see that the mea-
sured results are higher than the expectations in most cases. Given
this discrepancy exists between expectations and observations, we Figure 5. Distribution of the signal-to-noise ratio for our 5000 MC reali-
next proceed to quantify its significance by studying the distribu- sations (blue histograms), compared with the observations (red solid lines)
tion of the ISW signal-to-noise obtained using our 5000 mock maps and the theoretical expectations (green). The different green lines refer to:
of the galaxy surveys. We show these distributions in Fig. 5: here no shot noise (short-dashed), and shot noise included (long-dashed). The
we can see that they are broad, and the position of the observed S /N top panel shows each catalogue separately, the bottom panel is the full com-
is well within the expected scatter. In more detail, we fit a Gaussian bination, for which we also show the best-fit Gaussian distribution and its
parameters.
to the distribution of the mock total signal-to-noise, where we find
that the mean (i.e. the expectation for the total S /N from ΛCDM)
is 3.05, and the r.m.s. is 1 by construction. This places our observed
result 1.35 σ away from the mean. changing the thresholds in the extinction masks, or excluding parts
A further interesting point to be learnt from Fig. 5 is the com- of the data (such as the Southern hemisphere for the new SDSS
parison between theoretical S /N with (green solid lines) and with- DR8 galaxies). Another change which is typically at the same level
out (green dashed lines) shot noise. We can see that the effect of is produced if we decide to completely discard the pixels near the
shot noise is particularly large for the quasars, due to their limited edge of the survey, for which the mask weighting is fig < 1, in-
number density. From this we conclude that future measurements stead of correcting them with the appropriate weights. Furthermore
of extended quasar catalogues have the potential to significantly any extra large-scale power in the auto-correlation functions, which
improve the existing results, due to the large redshift coverage of could arise e.g. due to low-redshift contamination or other system-
these sources. atics, would increase the variance of the cross-correlations. We dis-
Given the number of different assumptions in the method of cuss this below in Section 5.3.2, showing that its effect is limited
the analysis, we roughly estimate that a systematic uncertainty of and in agreement with our systematic estimation of 0.4 σ.
≃ 0.4 needs to be included on the final figure of the signal-to-noise We have also checked the effect of removing any one cata-
ratio. For example, using other reasonable redshift distributions for logue from the analysis, finding in this case that the total signifi-
the catalogues typically results in changes of the signal-to-noise ra- cance can not be lowered below 3.9 σ, which is the result obtained
tio of the order 0.2 − 0.4. Similar differences are obtained when when ignoring the NVSS data.
c 2012 RAS, MNRAS 000, 1–19
10. 10 T. Giannantonio, R. Crittenden, R. Nichol and A. J. Ross
We publicly release the maps, masks, and results discussed
herein, which can be downloaded from the internet.3 Here one can
find for each of the six catalogues the following data: a file with the
Healpix galaxy map in FITS format, and its companion mask in the
same format; a table with the redshift distribution, and a table with
the results of the CCFs. Finally, the full covariance matrix based on
Monte Carlo maps is also provided.
4 SYSTEMATIC UNCERTAINTIES
Since the ISW signal is expected to be weak, possible systematic
uncertainties are a serious issue. Here we discuss some of the new
tests we have explored to constrain this contamination, and further
discussion can be found in G08 and earlier work.
4.1 Foreground contamination
While individual instrumental systematics are not expected to be Figure 6. Frequency dependence of the cross-correlations, for WMAP7:
correlated between surveys, the cross-correlation could be con- most results are stable compared with the size of the error bars. The error
taminated by extra-galactic sources in the microwave frequen- bars on 2MASS are again 0.5-σ.
cies, such as synchrotron emission or the Sunyaev-Zel’dovich ef-
fect. Our galaxy also emits in the microwave (dust, synchrotron
as discussed in G08 they are less severe than dust extinction for our
and free-free), so it is important to ensure that galactic structure
data.
does not creep into the large-scale structure measured in surveys;
otherwise spurious correlations with the CMB foregrounds will
bias the cosmological interpretation of the measurements. Another
possible source of cross-correlation is the secondary Doppler ef- For the DR7 MegaZ LRG data set there is excess power in the
fect which may be added to the CMB at the time or reionisation correlation with the CMB, at a similar level as found with DR6; ex-
(Giannantonio & Crittenden 2007); however, at the redshifts of cur- cess large-scale power has also been seen in the MegaZ LRG auto-
rently available data, this is expected to be completely subdomi- correlation function as discussed by Thomas et al. (2011a). While
nant. these excesses may be cosmological, they could also be evidence of
An important way to keep foreground contamination under remaining systematics, such as a higher than expected stellar con-
control is to check for dependence of the cross-correlation func- tamination. Recently, Ross et al. (2011b) improved the methods for
tions on the CMB frequency, as we expect the ISW signal to be selecting and interpreting an LRG catalogue, using a large spectro-
monochromatic while the extra-galactic and galactic foregrounds scopic training set from SDSS-III BOSS (Eisenstein et al. 2011).
sources such as SZ, synchrotron and dust are expected to have a These authors found that the most serious systematic problem with
strong frequency dependence. We have performed this test for the present photometric redshift catalogues from SDSS imaging is the
new data, and the results can be seen in Fig. 6; the cross-correlation failure to detect faint galaxies around foreground stars (even rela-
functions are quite stable relative to the measurement error bars tively faint stars to r ≃ 20). Ross et al. (2011b) corrected this is-
for the less contaminated WMAP maps (ILC, W, V, and largely Q). sue, but it does illustrate the need to be diligent about stellar con-
The most dependent on frequency is 2MASS, where Afshordi et al. tamination, especially when cross-correlating with other datasets
(2004) suggested there was evidence for the SZ effect; the most which may also include some contamination with galactic sources.
stable is HEAO, which is perhaps understandable as the hard X-ray In the future, catalogues with this higher level of systematics con-
background should be least affected by galactic contamination. trol should be used for the measurement of the ISW. The ISW signal
Perhaps the most worrying systematic problem which can af- seen in the LRG cross-correlation is higher than the ΛCDM expec-
fect the ISW measurement is the leakage of information from the tation; if future LRG data will be more in accord with ΛCDM, the
structure of our Milky Way into the galaxy catalogues. This can best-fit amplitude may well decline, but with the uncertainty also
potentially jeopardise the results, as it correlates with the CMB shrinking, the signal-to-noise ratio could remain at a similar level.
via residual dust extinction corrections. This problem can be min-
imised by masking sky areas closest to the galactic plane, and those
areas most affected by reddening, which we have done for all cata- 4.2 The rotation test
logues. Although the presence of systematic effects has been studied rather
We have also checked for the effect of removing from the carefully by several authors, it is possible some unaccounted un-
maps a band centred on either the ecliptic or galactic planes, us- certainty could remain in the data, thus compromising the measure-
ing cuts of different widths (10, 20 and 30 degrees). We have found ments, and it is therefore worthwhile to look for new ways to check
no significant differences. Other possibile systematics include the for such problems.
effects of point sources, regions of poor seeing and sky brightness; One such test, based on arbitrary rotations of the sky
maps, was recently proposed by Sawangwit et al. (2010). In this
test, cross-correlation functions (CCF) are generated by cross-
3 www.usm.lmu.de/˜tommaso/isw2012.php correlating the true maps, but after one of the maps has been rotated
c 2012 RAS, MNRAS 000, 1–19
11. The significance of the integrated Sachs-Wolfe effect revisited 11
4.2.1 Assessing the significance
One difficulty in making this comparison is that, for a given rotation
axis, there are a limited number of rotations which are independent
of one another due to the fact that the ISW signal is on relatively
large angles. We use 500 Monte Carlo simulations to evaluate this;
we create sets of CMB and galaxy maps with the expected signal
for the ΛCDM model, and rotate them as we do the real data. In the
top panel of Fig. 7 we show the average ‘zero-lag’ cross-correlation
as a function of rotation angle, with the 1-σ and 2-σ regions shaded
in green. We see that this is significant typically out to 30 degrees,
implying that this is the minimum rotation required to provide an
independent sample.
For any given rotation axis, this leaves only 11 independent
samples of the cross-correlation measure. If one or more of these
are significantly higher the the r.m.s. amplitude, then this could
be evidence for the systematic contamination. In the top panel of
Fig. 7 we plot the ‘zero-lag’ cross-correlation for each of our cat-
alogues. This shows that no significant outliers exist, and that the
signal is generally highest when there is no rotation, apart from
2MASS where the zero-lag signal could be cancelled by the SZ ef-
fect. This is quantified in Table 3, where we count the number of
rotations exceeding thresholds of 1-, 2σ (expected 32% and 5%); if
anything, the number of high correlations seen in the rotated maps
is lower than expected, though this discrepency is not significant.
The observed number above the threshold should be binomially dis-
tributed, which is very broad given the limited number of observa-
tions.
In S10, they looked instead at the number of rotations where
the ‘zero-lag’ cross-correlation exceeded the true ‘zero-lag’ cross-
correlation for that particular survey; that is, our zero degree value
(denoted w0i ). However, this is just one choice, with the drawback
of being different for each data set i. Nonetheless, we also show
this in Table 3. Again, for rotations about the galactic axis, we find
none exceeding the true value for our data sets.
We can increase our statistics and explore for the possibility of
Figure 7. The rotation test for our data, zero-lag case. In the top panel, for systematics associated with other reference frames by considering
each galaxy catalogue, we show the evolution of the CCF at 0 degrees as
rotations about other axes. We have repeated the test with rotations
a function of the arbitrary rotation angle ∆ϕ, describing rotations around
the galactic plane. The coloured lines show the observed results; the green
using: galactic, ecliptical, equatorial and supergalactic axes. For the
shaded bands indicate 1 and 2 σ regions calculated by generating 500 mock discussion below we ignore chance alignments of the various rota-
Monte Carlo maps of the data. The black dashed lines are the averages seen tions, but it should be kept in mind that all these points may not
in the same mock data, assuming a ΛCDM concordance model. The bot- be fully independent. The results are shown in the bottom panel of
tom panel shows the same test for rotations in different coordinate systems: Fig. 7. All of the rotations are consistent with the expected scat-
galactic, equatorial, ecliptic and supergalactic. ter, showing no indication for a preferred rotation axis. This seems
to support the hypothesis that the rotations are merely providing a
measure of the intrinsic scatter and are not suggestive of a contam-
inant associated with a single axis. The statistics are summarised
by some arbitrary angle ∆ϕ relative to the other. In Sawangwit et al. in Table 3, where we can see that only 31% and 3% of the points
(2010) rotations around the Galactic axis were chosen particularly lie above the 1-, 2-σ thresholds respectively. Excluding 2MASS,
to try to identify galactic contamination, but any axis choice is pos- only 3% exceed the true value measured in the data; unfortunately,
sible. For a sufficiently large rotation ∆ϕ, one expects on average this statistic cannot be used directly to estimate a total significance
that there will be no correlation, though any particular measure- because it will be dominated by maps with the least significant am-
ment will have scatter reflecting the intrinsic variance in the mea- plitude.
surement. (Any rotation leaves two poles fixed, implying a small For a visual impression of this, we plot our results in Fig. 8,
amount of residual correlation, but in practice this is negligible.) where the observed number of detections in excess of each thresh-
The critical question is, how do we evaluate the significance old is compared with the 68% confidence regions drawn from the
of the rotated correlation functions? The most obvious comparison continuous generalisation of a binomial probability distribution.
is to the variance of the intrinsic scatter, inferred from our Monte Here we can appreciate that the distribution of the points above the
Carlo simulations. Are the rotated correlation measurements con- 1- and 2-σ thresholds is fully consistent with the expected scatter
sistent with this intrinsic scatter or not? and the number of points above the the true measure levels seems
consistent with an average level of significance ∼ 2 σ for each cat-
alogue.
c 2012 RAS, MNRAS 000, 1–19