The 'End' State(s) of Galaxy Evolution

The 2nd law of thermodynamics is unavoidable. How does it play out in galaxy evolution? Specifically, are there any systems that we might regard as 'equilibrium' configurations in the present Universe? I explain why not in this talk.

Transcript

1. THE ‘END’ STATE(S) OF GALAXY EVOLUTION Alison Crocker ~ Reed College
2. Cosmic microwave background (Planck satellite) Diversity of galaxies (Hubble Space Telescope) Explain this process The quest of galaxy evolution:
3. 2nd law of thermodynamics: entropy always increases. ?
4. Entropy increases in gravitational collapse/ contraction. Collisional story: (think gas) Released grav. PE: 1/2 heats protostar, 1/2 radiated away (virial theorem) Radiated photons increase net entropy of the Universe.
5. Entropy does increase in gravitational collapse/ contraction. Collisional story: (think gas) Released grav. PE: 1/2 heats protostar, 1/2 radiated away (virial theorem) Radiated photons increase net entropy of the Universe. Collisionless story: (think stars in a galaxy) More of total 6D x N phase space occupied when inner region contracts, outer region expands. (Derivation Tremaine+ 1986).
6. ‘End state’ should be high (maximal?) entropy. Expect a centrally concentrated configuration.
7. OUTLINE ▸ Galaxy evolution: more than just stars ▸ ‘Textbook’ galaxy end state ▸ Fast rotating early-type galaxies ▸ Gas in fast rotators
8. CLASSIC GALAXY EVOLUTION Hubble’s original “tuning fork” diagram. (1936)
9. CLASSIC GALAXY EVOLUTION Hubble’s original “tuning fork” diagram. (1936) Presumed direction of galaxy evolution. “Early-type” galaxies. “Late-type” galaxies.
10. Hubble’s original “tuning fork” diagram. (1936) Actual direction of galaxy evolution (entropy compliant). CLASSIC GALAXY EVOLUTION
11. Classic picture considers early-types “red and dead”. NGC 3559 CLASSIC GALAXY EVOLUTION
12. A GALAXY IS MORE THAN IT’S STARS… dark matter • stars • gas and dust • supermassive blackholes
13. A GALAXY IS MORE THAN IT’S STARS… dark matter • stars • gas and dust • supermassive blackholes Illustris simulation. Now, z=0 z=4 Backbone of galaxy evolution: galaxies form where dark matter has previously clumped.
14. A GALAXY IS MORE THAN IT’S STARS… dark matter • stars • gas and dust • supermassive blackholes Hirschmann et al. 2012 Dark matter merger trees.
15. A GALAXY IS MORE THAN IT’S STARS… dark matter • stars • gas and dust • supermassive blackholes
16. A GALAXY IS MORE THAN IT’S STARS… dark matter • stars • gas and dust • supermassive blackholes M51, “Whirlpool Galaxy”, Credit: Lopez-Sanchez, Anglo-Australian Observatory. hot gas cool gas cold gas dust
17. A GALAXY IS MORE THAN IT’S STARS… dark matter • stars • gas and dust • supermassive blackholes Thorne and Interstellar team Centaurus A, with radio jets from black hole.
18. A GALAXY IS MORE THAN IT’S STARS… dark matter • stars • gas and dust • supermassive blackholes TRUE END STATE REQUIREMENT: all of these components should remain ~constant in time…
19. TEXTBOOK ‘END’ STATE HST image, M87, Virgo Cluster
20. STARS ▸ r1/4 logarithmic light intensity profiles (de Vaucouleurs) ▸ as predicted for collisionless gravitational collapse of initially clumpy systems (i.e. mergers) Ferrarese + 2006 THE TEXTBOOK END STATE
21. x THE TEXTBOOK END STATE STARS ▸ ‘Dispersion’ (as opposed to rotation) dominated. Filling up lots of available phase space, less ordered, high entropy. Filling up little phase space, highly ordered, low entropy.
22. THE TEXTBOOK END STATE GAS ▸ Essentially an ‘atmosphere’ of hot, X-ray emitting gas T ~ 107 K X-ray images of galaxies, Werner et al. 2014 X-ray images of galaxy clusters, Morandi et al. 2016 T ~ 106 K
23. GAS ▸ gas is cooling all the time ▸ instabilities develop in the atmosphere -> precipitation of the gas toward center ▸ subsequent star formation and black hole growth! THE TEXTBOOK END STATE Sutherland + Dopita cooling curve, 1981
24. GAS Li, Yuan + 2015 THE TEXTBOOK END STATE
25. GAS -> STARS, BLACK HOLE Li, Yuan + 2015 THE TEXTBOOK END STATE
26. Textbook: 1. Dispersion-dominated stars 2. Radiating hot gas, ‘maintained’ by AGN feedback. ‘END’ STATES
27. FAST-ROTATING EARLY-TYPE GALAXIES NGC 2768, Credit: Martin Germano
28. FAST ROTATORS OBSERVATIONS: ▸ Most early-type galaxies have a clear sense of rotation THEORY: ▸ Of course! Where did you think the angular momentum went?
29. OBSERVATIONS: ▸ Select a representative early-type galaxy sample Project FAST ROTATORS
30. OBSERVATIONS: ▸ Select a representative early-type galaxy sample Project FAST ROTATORS
31. OBSERVATIONS: ▸ Select a representative early-type galaxy sample Project End sample: 260 early-type galaxies FAST ROTATORS
32. OBSERVATIONS: ▸ Obtain resolved spectroscopy for every galaxy William Herschel Telescope SAURON spectrograph FAST ROTATORS
33. OBSERVATIONS: ▸ Obtain resolved spectroscopy for every galaxy William Herschel Telescope SAURON spectrograph FAST ROTATORS
34. SDSS “Early-type galaxy” template FAST ROTATORS Atlas3d spectral coverage
35. RESULTS! Velocity maps for 260 sample galaxies. FAST ROTATORS
36. RESULTS! Slow rotators. Fast rotators. FAST ROTATORS
37. RESULTS! Slow rotators. 36/260. Fast rotators. 224/260. FAST ROTATORS
38. QUANTIFY Dimensionless spin parameter. Peebles 1969 Observable approximation to dimensionless spin parameter. Emsellem et al. 2007 FAST ROTATORS
39. WHICH GALAXIES ROTATE FAST/SLOW? FAST ROTATORS Highest-mass galaxies all rotate slowly. Emsellem et al. 2011
40. HOW TO MAKE A SLOW/FAST ROTATOR FAST ROTATORS
41. HOW TO MAKE A SLOW/FAST ROTATOR FAST ROTATORS Two fast rotator scenarios: Time -> Naab et al. 2014 Stellar mass Stellar ang. momentum
42. HOW TO MAKE A SLOW/FAST ROTATOR FAST ROTATORS Two fast rotator scenarios: Time -> Stellar mass Stellar ang. momentum Naab et al. 2014
43. HOW TO MAKE A SLOW/FAST ROTATOR FAST ROTATORS Two slow rotator scenarios: Time -> Stellar mass Stellar ang. momentum Naab et al. 2014
44. Slow rotator: 1. Dispersion-dominated stars 2. Radiating hot gas, ‘maintained’ by AGN feedback. ‘END’ STATES Fast rotator: 1. Stellar rotation important! 2. Gas?
45. WHAT IS THE GAS DOING IN FAST ROTATORS?
46. OBSERVATIONS: Project GAS Cold, molecular gas: - Millimeter dish/ interferometer Cool, atomic gas: - Radio interferometer Warm, ionized gas: - Resolved optical spectroscopy Hot, ionized gas: - X-ray telescope IRAM 30m CARMA WHT WRST Chandra
47. COLD, MOLECULAR GAS: GAS - Millimeter dish/interferometer - Trace with CO (carbon monoxide) rotational emission lines - 22% of galaxies detected in CO(1-0) line - 107-109 solar masses of H2 Crocker et al. 2012
48. COOL, ATOMIC GAS: GAS - Radio interferometer - Trace with hyperfine HI line at 21 cm - 33% of galaxies detected in 12h of observing - 107-109.5 solar masses of atomic H Serra et al. 2013
49. WARM, IONIZED GAS: GAS - Resolved optical spectroscopy - Trace with hydrogen recombination lines, metallic forbidden lines - 75% of galaxies detected - 104-105 solar masses of H+ Sarzi et al. 2006
50. HOT, IONIZED GAS: GAS - X-ray telescopes - Trace with thermal brehmstrahlung - 20% of galaxies detected with hot gas distinguishable from X-ray binaries - ~109-1011 solar masses of hot H+ Sarzi et al. 2013
51. GAS Cold gas Cool gas Warm gas Hot gas Expected, hot atmosphere of gas.
52. GAS ORIGINS Cold gas Cool gas Warm gas Hot gas What is origin of this gas? Options: 1) Cooling flow 2) Remnant from earlier spiral phase 3) Externally accreted } } Should corotate with stars Random rotation with respect to stars
53. molecular gas stars NGC 524 NGC 2768 co-rotation of gas polar rotation of gas Ψmol-star ≅ 0° Ψmol-star ≅ 90° GAS ORIGINS
54. Cluster galaxies: almost all co-rotate Field galaxies: only half co-rotate Davis et al. 2011 GAS ORIGINS
55. Davis et al. 2011 Cluster galaxies: very, very little external accretion Field galaxies: about 50% of gas externally accreted GAS ORIGINS
56. Cluster galaxies: very, very little external accretion Field galaxies: about 50% of gas externally accreted GAS ORIGINS Ongoing external accretion in HI maps.
57. cluster non-cluster But, cold gas detection fractions are the same in and out of the cluster… GAS ORIGINS
58. cluster non-cluster But, cold gas detection fractions are the same in and out of the cluster… If the field has an additional cold-gas supply, so must the cluster, to remain equal. Cooling flow? Remnant from earlier spiral phase? GAS ORIGINS
59. cluster non-cluster But, cold gas detection fractions are the same in and out of the cluster… If the field has an additional cold-gas supply, so must the cluster, to remain equal. Cooling flow? Remnant from earlier spiral phase? GAS ORIGINS
60. Cooling flow? Remnant from earlier spiral phase? GAS ORIGINS A galaxy suffering ram- pressure stripping in the Virgo cluster. (HST image)
61. GAS ORIGINS Cold gas Cool gas Warm gas Hot gas What is fate of this gas? Options: 1) Star formation 2) AGN feeding
62. GAS ORIGINS Cold gas Cool gas Warm gas Hot gas What is fate of this gas? Options: 1) Star formation 2) AGN feeding Martig, Crocker + 2012
63. Slow rotators: 1. Dispersion-dominated stars 2. Radiating hot gas, ‘maintained’ by AGN feedback. EARLY-TYPE GALAXY END STATES Fast rotators: 1. Rotation-dominated stars (thanks to angular momentum) 2. Variety of gas origins and fates!
64. In all of these cases, entropy-increasing processes are still underway. Mass is redistributing itself from gas to stars to blackholes. No galaxy is ‘dead’. CONCLUSION