A1 22 Active Galaxies

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A1 22 Active Galaxies

  1. 1. Active Galaxies: Types LACC: Ch 26 • Seyfert Galaxies • Radio Galaxies • Quasars An attempt to answer the “big questions”: what is out there? how did we get here? Thursday, May 13, 2010 1
  2. 2. Active Galaxies Normal vs active galaxies: Normal ones are basically made of stars emitting visible light; Active ones are much brighter and have a different, "nonstellar" spectrum. http://www.phy.olemiss.edu/~luca/astr/Topics-Extrasolar/Active-N.html Thursday, May 13, 2010 2
  3. 3. Active Galaxies http://www.astr.ua.edu/keel/agn/seyferts.html Thursday, May 13, 2010 3
  4. 4. Active Galaxies: Seyfert Galaxies All these galaxies show the characteristic intense, point-like nucleus originally remarked for this class by Carl Seyfert. The galaxies' Hubble types are also representative for Seyfert galaxies as a group, dominated by ... spirals (Sa and Sb, with both barred and non-barred representatives) and S0 systems. These are V-band images.... logarithmic intensity mapping was used to enhance the visibility of both bright and faint structure. http://www.astr.ua.edu/keel/agn/seyferts.html Thursday, May 13, 2010 4
  5. 5. Active Galaxies: Radio Galaxies http://www.astr.ua.edu/keel/agn/radgal.html Thursday, May 13, 2010 5
  6. 6. Active Galaxies: Radio Galaxies One remarkable finding from HST images, barely anticipated from the ground, is that dust structures close to the nucleus are prevalent in radio galaxies. These structure often take the form of disks or rings, at right angles to the radio jets and thus fitting with the general picture of jets collimated by the influence of an accretion disk surrounding the central objects. These are far too large to be the active, hot accretion disk itself, which should extend to no more than light-months in radius, but may represent material which has already settled into its orbital plane and will eventually migrate inwards into such an accretion disk. These are red-light ... images.... A logarithmic intensity scale is used to make detail visible over a wide brightness range. The scale bars indicate one arc-second. http://www.astr.ua.edu/keel/agn/radgal.html Thursday, May 13, 2010 6
  7. 7. Quasars http://chandra.harvard.edu/xray_sources/quasars.html Thursday, May 13, 2010 7
  8. 8. Quasars Quasars are peculiar objects that radiate as much energy per second as a thousand or more galaxies, from a region that has a diameter about one millionth that of the host galaxy. It is as if a powerhouse the size of a small flashlight produced as much light as all the houses and businesses in the entire L.A. basin! Quasars are intense sources of X-rays as well as visible light. They are the most powerful type of X-ray source yet discovered. Some quasars are so bright that they can be seen at a distance of 12 billion light years. http://chandra.harvard.edu/xray_sources/quasars.html Thursday, May 13, 2010 8
  9. 9. Quasar http://www.astr.ua.edu/keel/agn/pks1117r.html Thursday, May 13, 2010 9
  10. 10. Quasars With ground-based telescopes, quasars are typically boring until you measure their spectrum. As a pretty typical example, this is the radio-loud quasar PKS 1117-248 at redshift z=0.466 [~1.5 billion parsecs]. I marked it to reduce puzzlement - this image shows why various subterfuges involving radio emission, X-rays, colors, or spectra are needed to pick out quasars wholesale from foreground stars. Even at this modest redshift, there's not much of a host galaxy or surrounding group visible to make it stand out. This is a red-light CCD image.... The image covers an area 2.9 by 2.9 arcminutes. http://www.astr.ua.edu/keel/agn/pks1117r.html Thursday, May 13, 2010 10
  11. 11. Active Galactic Nuclei, AGN The unification scheme explains the connection between different types of radio- loud AGNs. It is based on the orientation of the AGNs disk to the observer. When the radio-loud AGN is observed disks edge-on, i.e the central area is blocked from the direct view, a radio galaxy is seen. If the radiation from central torus is observed without it being blocked by the central torus, the quasar is seen. http://www.mpa-garching.mpg.de/HIGHLIGHT/2003/highlight0301_e.html Thursday, May 13, 2010 11
  12. 12. Active Galaxies vs. Quasars Seyfert galaxies, radio galaxies, and quasars are similar objects -- accretion powered active nuclei. They may differ in total luminosity (quasars vs active galaxies) or in radio power (seyfert 1’s vs radio galaxies/seyfert 2’s) or in host galaxies (seyferts vs radio galaxies). http://abyss.uoregon.edu/~js/ast123/lectures/lec12.html Thursday, May 13, 2010 12
  13. 13. Active Galaxies: Types LACC: Ch 26 • Seyfert Galaxies: Active Spiral Galaxies, non- stellar spectrum • Radio Galaxies: Active Elliptical Galaxies, non- stellar spectrum • Quasars: Super Active Galaxies, non-stellar spectrum An attempt to answer the “big questions”: what is out there? how did we get here? Thursday, May 13, 2010 13
  14. 14. LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 26, pp. 601: 3. Due at the beginning of next week’s first class period (unless there is a test that week, in which case it’s due the same period as the test). Be working on your Distance Ladders. Thursday, May 13, 2010 14
  15. 15. Active Galaxies: Cause LACC: Ch 26 • Active Galaxies Power Source • Active Galaxies Causes • Observations An attempt to answer the “big questions”: what is out there? how did we get here? Thursday, May 13, 2010 15
  16. 16. Active Galactic Nuclei, AGN http://www.astronomynotes.com/galaxy/s12.htm Thursday, May 13, 2010 16
  17. 17. Active Galactic Nuclei, AGN Active galactic nuclei (hereafter abbreviated AGNs) are among the most spectacular objects in the Universe. They produce prodigious luminosities (in some cases as much as 10,000 times the luminosity of a typical galaxy) in tiny volumes (much less than one cubic parsec). Most astronomers now believe that the power for AGNs comes from accretion onto the supermassive black holes located at the centre of every galaxy with a bulge. http://www.mpa-garching.mpg.de/HIGHLIGHT/2003/highlight0301_e.html Thursday, May 13, 2010 17
  18. 18. Active Galactic Nuclei, AGN The dark, dusty disk represents a cold outer region, which moves inward to within a few hundred million miles of the suspected black hole. This disk feeds matter into the black hole, where gravity compresses and heats the material. Some hot gas squirts out from the black hole's near-vicinity to create the radio jets. http://teacherlink.ed.usu.edu/tlnasa/pictures/litho/NGC4261/ncg4261.html Thursday, May 13, 2010 18
  19. 19. Active Galactic Nuclei, AGN A torus of dusty material is thought to surround the accreting black holes in most AGN. Radiation which escapes perpendicular to the torus is able to ionize gas clouds in the surrounding galaxy, which leads to characteristic emisson line signatures in the galaxy spectrum. http://www.mpa-garching.mpg.de/HIGHLIGHT/2003/highlight0301_e.html Thursday, May 13, 2010 19
  20. 20. Active Galactic Nuclei, AGN Active galaxies are also noteworthy in that they display very strong cosmological evolution. The most luminous active galaxies were a thousand times more numerous at redshift 2.5 than they are today. This strong evolution with redshift suggests that galaxy formation and the creation of active nuclei may have gone hand-in-hand in the early Universe. The main conclusion reached by the MPA/JHU team is that strong AGN activity is often associated with strong bursts of recent star formation in the host galaxy. http://www.mpa-garching.mpg.de/HIGHLIGHT/2003/highlight0301_e.html Thursday, May 13, 2010 20
  21. 21. Quasars: a normal stage? It has long been clear that the quasars we can observe evolve strongly with cosmic time, having gone through a peak about 12 billion years ago when a large fraction of bright galaxies must have hosted quasars, and with their number falling dramatically down to the present day. Going outward in redshift and farther back in time, the number of quasars (at least the very powerful ones that we could find so far away) declines above redshift z=4, with progressively fewer and fewer up to the current record at z=6.4. Either we are watching the population of quasars "turn on", or for some reason we can't find most of the high-redshift quasars that were there. http://universe-review.ca/I05-22-CentaurusA.jpg Thursday, May 13, 2010 21
  22. 22. Quasars -> Active -> Normal A possible evolutionary sequence for galaxies, beginning with the highly luminous quasars, decreasing in violence through the radio and Seyfert galaxies, and ending with normal spirals and ellipticals. The central black holes that powered the early activity are still there at later times; they simply run out of fuel as time goes on. http://lifeng.lamost.org/courses/astrotoday/CHAISSON/AT325/HTML/AT32506.HTM Thursday, May 13, 2010 22
  23. 23. Active Galactic Nuclei, AGN The core of the Seyfert 2 galaxy NGC 7742. The lumpy thick ring around the core is an area of active star formation. The ring is about 3000 light-years from the core. http://www.mpa-garching.mpg.de/ HIGHLIGHT/2003/highlight0301_e.html Thursday, May 13, 2010 23
  24. 24. Active Galaxies: mergers? http://www.whatsnextnetwork.com/ technology/index.php/2007/ Thursday, May 13, 2010 24
  25. 25. Centaurus A This galaxy is situated in It is of intermediate type the M83 group of galaxies. between elliptical and It is one of the most disk (spiral) galaxies: interesting and peculiar The main body galaxies in the sky, and is a has all strong source of radio characteristics radiation (therefore the of a large designation Centaurus A); elliptical, but a it is actually the nearest pronounced radio galaxy. dust belt is superimposed well over the center, forming a disk plane around this galaxy. This galaxy seems to have "eaten" at least one larger spiral in the last few billion years. http://www.seds.org/ messier/xtra/ngc/n5128.html Thursday, May 13, 2010 25
  26. 26. Centaurus A A fantastic jumble of young blue star clusters, gigantic glowing gas clouds, and imposing dark dust lanes surrounds the central region of the active galaxy Centaurus A. This mosaic of Hubble Space Telescope images taken in blue, green, and red light has been processed to present a natural color picture of this cosmic maelstrom. Infrared images from the Hubble have also shown that hidden at the center of this activity are what seem to be disks of matter spiraling into a black hole with a billion times the mass of the Sun! Centaurus A itself is apparently the result of a collision of two galaxies and the left over debris is steadily being consumed by the black hole. Astronomers believe that such black hole central engines generate the radio, X-ray, and gamma-ray energy radiated by Centaurus A and other active galaxies. But for an active galaxy Centaurus A is close, a mere 10 million light-years away, and is a relatively convenient http://apod.nasa.gov/ laboratory for exploring these powerful sources of energy. apod/ap070729.html Thursday, May 13, 2010 26
  27. 27. Centaurus A Peering deep inside Centaurus A, the closest active galaxy to Earth, the Spitzer Space Telescope's penetrating infrared cameras recorded this startling vista. About 1,000 light-years across, the twisted cosmic dust cloud apparently shaped like a parallelogram is likely the result of a smaller spiral galaxy falling into the giant Centaurus A. The parallelogram lies along the active galaxy's central band of dust and stars visible in more familiar optical images. Astronomers believe that the striking geometric shape represents an approximately edge-on view of the infalling spiral galaxy's disk in the process of being twisted and warped by the interaction. Ultimately, debris from the ill-fated spiral galaxy should provide fuel for the supermassive black hole lurking at the center of Centaurus A. http://apod.nasa.gov/apod/ap040624.html Thursday, May 13, 2010 27
  28. 28. Centaurus A Its core hidden from optical view by a thick lane of dust, the giant elliptical galaxy Centaurus A was among the first objects observed by the orbiting Chandra X-ray Observatory. Astronomers were not disappointed, as Centaurus A's appearance in x-rays makes its classification as an active galaxy easy to appreciate. Perhaps the most striking feature of this Chandra false-color x-ray view is the jet, 30,000 light- years long. Blasting toward the upper left corner of the picture, the jet seems to arise from the galaxy's bright central x-ray source -- suspected of harboring a black hole with a million or so times the mass of the Sun. Centaurus A is also seen to be teeming with other individual x-ray sources and a pervasive, diffuse x-ray glow. Most of these individual sources are likely to be neutron stars or solar mass black holes accreting material from their less exotic binary companion stars. The diffuse high-energy glow represents gas throughout the galaxy heated to temperatures of millions of degrees C. At 11 million light-years distant in the constellation Centaurus, Centaurus A (NGC 5128) is the closest active galaxy. http://apod.nasa.gov/apod/ap030705.html Thursday, May 13, 2010 28
  29. 29. Centaurus A A radio image of the same galaxy reveals a dramatically different view: giant radio lobes are emerging perpendicular to the dust lane. http://archive.ncsa.uiuc.edu/Cyberia/NumRel/RelUniverse2.html Thursday, May 13, 2010 29
  30. 30. Centaurus A http://universe-review.ca/I05-22-CentaurusA.jpg Thursday, May 13, 2010 30
  31. 31. Active Galaxies: Cause LACC: Ch 26 • Active Galaxies Power Source: an Active Galactic Nucleus [AGN]--matter in an accretion disc spiraling in to a supermassive black hole • Active Galaxies Causes: a normal part of early galaxy development and/or galaxy mergers • Observations: X-rays (from accretion disc and jets), visible (bright galaxy nucleus), infrared (dust waiting to be eaten), radio (lobes larger than the galaxy itself) An attempt to answer the “big questions”: what is out there? how did we get here? Thursday, May 13, 2010 31
  32. 32. LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch 27: Tutorial Quizzes accessible from: http:// www.brookscole.com/cgi-brookscole/course_products_bc.pl? fid=M20b&product_isbn_issn=9780495017899&discipline_number=19 Due at the beginning of next week’s first class period (unless there is a test that week, in which case it’s due the same period as the test). Be working on your Distance Ladders. Thursday, May 13, 2010 32

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