1 / 53

ACTIVE GALAXIES and GALAXY EVOLUTION

ACTIVE GALAXIES and GALAXY EVOLUTION. Quasars, Radio Galaxies, Seyfert Galaxies and BL Lacertae Objects Immense powers emerging from ACTIVE GALACTIC NUCLEI: it’s just a phase they’re going through!. How do we observe the life histories of galaxies?.

harry
Télécharger la présentation

ACTIVE GALAXIES and GALAXY EVOLUTION

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ACTIVE GALAXIES and GALAXY EVOLUTION Quasars, Radio Galaxies, Seyfert Galaxies and BL Lacertae Objects Immense powers emerging from ACTIVE GALACTIC NUCLEI: it’s just a phase they’re going through!

  2. How do we observe the life histories of galaxies?

  3. Deep observations show us very distant galaxies as they were much earlier in time (Old light from young galaxies)

  4. How did galaxies form?

  5. We still can’t directly observe the earliest galaxies

  6. Our best models for galaxy formation assume: • Matter originally • filled all of space • almost uniformly • Gravity of denser • regions pulled in • surrounding • matter

  7. Denser regions contracted, forming protogalactic clouds H and He gases in these clouds formed the first stars

  8. Supernova explosions from first stars kept much of the gas from forming stars Leftover gas settled into spinning disk Conservation of angular momentum

  9. NGC 4414 M87 But why do some galaxies end up looking so different?

  10. Why do galaxies differ?

  11. Why don’t all galaxies have similar disks?

  12. Conditions in Protogalactic Cloud? Spin: Initial angular momentum of protogalactic cloud could determine size of resulting disk

  13. Conditions in Protogalactic Cloud? Density: Elliptical galaxies could come from dense protogalactic clouds that were able to cool and form stars before gas settled into a disk Elliptical vs. Spiral Galaxy Formation

  14. Start with the Mildly Active or Peculiar Galaxies • STARBURST galaxies -- 100's of stars forming per year, but spread over some 100's of parsecs. • Other PECULIAR galaxies involve collisions or mergers between galaxies. • Sometimes produce strong spiral structure (e.g. M51, the "Whirlpool") • Sometimes leave long tidal tails (e.g. the "Antennae" galaxies) • Sometimes leave "ring" galaxy structures--an E passing through a S. • Sometimes see shells of stars around Es

  15. Peculiar Galaxies: Starburst (NGC 7742) , Whirlpool (M51), Antennae (NGC 4038/9) in IR, Ring (AM 0644-741)

  16. Colliding Galaxies • “Cartwheel” ring galaxy • Antennae, w/ starbursts and a simulation: a collision in progress • Collision Simulation Movie

  17. Collisions may explain why elliptical galaxies tend to be found where galaxies are closer together

  18. Giant elliptical galaxies at the centers of clusters seem to have consumed a number of smaller galaxies

  19. Starburst galaxies are forming stars so quickly they would use up all their gas in less than a billion years

  20. 4 MAIN CLASSES of AGN • Radio Galaxies • Quasars • Seyfert Galaxies • BL Lacertae Objects (or Blazars with some Quasars and some Radio Galaxies) • All are characterized by central regions with NON-THERMAL radiation dominating over stellar (thermal) emission

  21. Thermal vs. Non-Thermal Spectra Normal mostly from stars, Active mostly synchrotron

  22. RADIO GALAXIES • All are in Elliptical galaxies • Two oppositely directed JETS emerge from the galactic nucleus • They often feed HOT-SPOTS and and LOBES on either side of the galaxy • Radio source sizes often 300 kpc or more --- much bigger than their host galaxies. • Head-tail radio galaxies arise when jets are bent by the ram-pressure of gas as the host galaxy moves through it. • For powerful sources only one jet is seen: this is because of RELATIVISTIC DOPPER BOOSTING: the approaching jet appears MUCH brighter than an intrinsically equal receding jet since moving so FAST; • Can yield CORE DOMINATED RGs

  23. Radio Galaxy: Centaurus A

  24. Cygnus A and M87 Jet

  25. Radio Lobes Dwarf Big Galaxy

  26. Core Dominated RG (M86)

  27. QUASAR PROPERTIES • QUASI-STELLAR-OBJECT: (QSO): i.e., it looks like a STAR BUT: NON-THERMAL SPECTRUM UV excess (not like a star) • BROAD EMISSION LINES  Rapid motions • VERY HIGH REDSHIFTS  not a star, but FAR away. The current (2008) convincing record redshift is z = 6.4, i.e., light emitted in FAR UV at 100 nm is received by us in the near IR at 740 nm! • HUGE DISTANCES  VERY LUMINOUS

  28. NEWER QUASAR DISCOVERIES • Only about 10% are RADIO LOUD • Most show some VARIABILITY in POWER • OVV (Optically Violently Variable) QUASARS change brightness by 50% or more in a year and are highly polarized • QUASARS are AGN: surrounding galaxies detected, though small nucleus emits 10-1000 times MORE light than 1011 stars! “Brighter than a TRILLION suns”

  29. Quasar 3C 273 • Radio loud • Rare OPTICAL jet, but otherwise looks like a star • Relatively nearby quasar

  30. Redshifted Spectrum of 3C 273

  31. Typical Quasar Appearance • Most are actually very faint • BUT their huge redshifts imply they are billions of light-years away and intrinsically POWERFUL

  32. Radio Loud Quasar, 3C 175

  33. Thought Question What can you conclude from the fact that quasars usually have very large redshifts? A. They are generally very distant B. They were more common early in time C. Galaxy collisions might turn them on D. Nearby galaxies might hold dead quasars

  34. Thought Question What can you conclude from the fact that quasars usually have very large redshifts? A. They are generally very distant B. They were more common early in time C. Galaxy collisions might turn them on D. Nearby galaxies might hold dead quasars All of the above!

  35. Birth of a Quasar Movie • Fast variability implies small size • Immense powers emerging from a volume similar to the solar system!

  36. SEYFERT GALAXIES • Sa, Sb galaxies with BRIGHT, SEMI-STELLAR NUCLEI • NON-THERMAL & STRONG EMISSION LINES • VARIABLE in < 1 yr  COMPACT CORE • Type 1: Broad Emission lines (like QSOs), strong in X-rays • Type 2: Only narrow Emission lines, weak in X-rays • About 1% of all Spirals are SEYFERTS, so • Either 1% of all S's are always Seyferts OR • 100% of S's are Seyferts for about 1% of the time (MORE LIKELY) • OR 10% of S's are Seyferts for about 10% of the time (or any other combination of fraction and lifetime)

  37. A Seyfert and X-ray Variability • Circinus, only 4 Mpc away; 3C 84

  38. More About Seyferts • Seyferts are weak radio emitters. • CONCLUSIONS ABOUT SEYFERTS Fundamentally, they are WEAKER QSOs • Type 1: we see the center more directly Type 2: dusty gas torus blocks view of the center

  39. BL Lacertae Objects • NON-THERMAL SPECTRUM: Radio through X-ray (and gamma-ray) • Radiation strongly POLARIZED • HIGHLY VARIABLE in ALL BANDS • But (when discovered) NO REDSHIFT, so distances unknown • Later, surrounding ELLIPTICAL galaxies found • CONCLUSION: greatly enhanced emission from the AGN due to RELATIVISTIC BOOSTING of a JET pointing very close to us. • BL Lacs + OPTICALLY VIOLENTLY VARIABLE QUASARS ARE OFTEN CALLED BLAZARS

  40. AGN CONTAIN SUPERMASSIVE BLACK HOLES (SMBHs) • KEY LONGSTANDING ARGUMENTS: • ENERGETICS: Powers up to 1048 erg/s (1041W) Even at 100% efficiency would demand conversion of about 18 M /yr (=Mdot) into energy. • Nuclear processes produce < 1% efficiency. • GRAVIATIONAL ENERGY via ACCRETION can produce between 6% (non-rotating BH) and 32% (fastest-rotating BH),and the Luminosity is • L = G MBH Mdot / R, • with R the main distance from the Super Massive Black Hole (SMBH) where mass is converted to energy.

  41. Time Variability • tVAR = R / c • tVAR = 104 s  • R = 3 x 1014 cm = 10-4 pc • For L = 1047 erg/s, • M_dot = 10 M /yr we get MBH = 3 x 108 M and RS = 9 x 1013 cm • So, R = 3 RS • MUTUALLY CONSISTENT POWERS AND TIMESCALES.

  42. RECENT OBSERVATIONAL SUPPORT • The Hubble Space Telescope has revealed that star velocities rise to very high values close to center of many galaxies and gas is orbiting rapidly, e.g. M87 • Disks have been seen via MASERS in some nearby Seyfert AGN. • VLBI: radio jets formed within 1 pc of center. • There are several other more technical lines of evidence also supporting the SMBH hypothesis for AGN.

  43. Rapidly Rotating Gas in M87 Nucleus M87 zoom toward black hole

  44. Direct Evidence for Rotating Disk Masers formed in warped disk in NGC 4258 (and a few other Seyfert galaxies)

  45. Evidence for Supermassive Black Holes NGC 4261: at core of radio emitting jets is a clear disk ~300 light-yrs across and knot of emission near BH

  46. SMBH Model for AGN

  47. UNIFIED MODELS FOR AGN • Three main parameters: MBH; the accretion rate, M_dot, and viewing angle to the accretion disk axis,  • Main ingredients: • SMBH > 106 M • 10-5 pc < accretion disk < 10-1 pc (AD) • broad line clouds < 1 pc (BLR) • thick, dusty, torus < 100 pc • narrow line clouds < 1000 pc (NLR) • sometimes, a JET (usually seen from < 102 pc to maybe 106 pc!)

  48. RADIO QUIET High MBH, M_dot:  small: QSO is seen including AD and BLR  large: only NLR plus radiating torus: seen as UltraLuminous InfraRed Galaxies (ULIRGs) Low MBH, M_dot:  small: Seyfert Type 1  big: Seyfert Type 2 RADIO LOUD (Jets) High MBH, M_dot:  very small: Optically Violently Variable Quasar  small: radio loud quasar (QSR)  large: classical double radio galaxy (FR II type) Low MBH. M_dot:  very small: BL Lac object  small: broad line radio galaxy (FR I type)  large: narrow line radio galaxy Unification for Radio Quiet and Radio Loud

More Related