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THE ‘END’ STATE(S) OF GALAXY EVOLUTION
Alison Crocker ~ Reed College
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Cosmic microwave background (Planck satellite)
Diversity of galaxies (Hubble Space Telescope)
Explain this process
The quest of galaxy
evolution:
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2nd law of thermodynamics: entropy always
increases.
?
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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.
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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).
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‘End state’ should be high (maximal?) entropy.
Expect a centrally concentrated configuration.
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OUTLINE
▸ Galaxy evolution: more than just stars
▸ ‘Textbook’ galaxy end state
▸ Fast rotating early-type galaxies
▸ Gas in fast rotators
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CLASSIC GALAXY EVOLUTION
Hubble’s original “tuning fork” diagram. (1936)
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CLASSIC GALAXY EVOLUTION
Hubble’s original “tuning fork” diagram. (1936)
Presumed direction of galaxy evolution.
“Early-type” galaxies.
“Late-type” galaxies.
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Hubble’s original “tuning fork” diagram. (1936)
Actual direction of galaxy evolution (entropy compliant).
CLASSIC GALAXY EVOLUTION
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Classic picture considers early-types “red and dead”.
NGC 3559
CLASSIC GALAXY EVOLUTION
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A GALAXY IS MORE THAN IT’S STARS…
dark matter ● stars ● gas and dust ● supermassive blackholes
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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.
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A GALAXY IS MORE THAN IT’S STARS…
dark matter ● stars ● gas and dust ● supermassive blackholes
Hirschmann et al. 2012
Dark matter merger trees.
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A GALAXY IS MORE THAN IT’S STARS…
dark matter ● stars ● gas and dust ● supermassive blackholes
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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
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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.
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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…
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TEXTBOOK ‘END’ STATE
HST image, M87, Virgo Cluster
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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
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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.
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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
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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
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GAS
Li, Yuan + 2015
THE TEXTBOOK END STATE
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GAS -> STARS, BLACK HOLE
Li, Yuan + 2015
THE TEXTBOOK END STATE
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Textbook:
1. Dispersion-dominated stars
2. Radiating hot gas, ‘maintained’ by
AGN feedback.
‘END’ STATES
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FAST-ROTATING EARLY-TYPE GALAXIES
NGC 2768, Credit: Martin Germano
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FAST ROTATORS
OBSERVATIONS:
▸ Most early-type galaxies
have a clear sense of
rotation
THEORY:
▸ Of course! Where did
you think the angular
momentum went?
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OBSERVATIONS:
▸ Select a representative early-type galaxy sample
Project
FAST ROTATORS
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OBSERVATIONS:
▸ Select a representative early-type galaxy sample
Project
FAST ROTATORS
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OBSERVATIONS:
▸ Select a representative early-type galaxy sample
Project
End sample:
260 early-type galaxies
FAST ROTATORS
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OBSERVATIONS:
▸ Obtain resolved spectroscopy for every galaxy
William Herschel
Telescope
SAURON spectrograph
FAST ROTATORS
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OBSERVATIONS:
▸ Obtain resolved spectroscopy for every galaxy
William Herschel
Telescope
SAURON spectrograph
FAST ROTATORS
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SDSS “Early-type galaxy” template
FAST ROTATORS
Atlas3d spectral coverage
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RESULTS!
Velocity maps for 260 sample galaxies.
FAST ROTATORS
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RESULTS!
Slow rotators. Fast rotators.
FAST ROTATORS
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RESULTS!
Slow rotators. 36/260. Fast rotators. 224/260.
FAST ROTATORS
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QUANTIFY
Dimensionless spin parameter.
Peebles 1969
Observable approximation to
dimensionless spin parameter.
Emsellem et al. 2007
FAST ROTATORS
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WHICH GALAXIES ROTATE FAST/SLOW?
FAST ROTATORS
Highest-mass galaxies all
rotate slowly.
Emsellem et al. 2011
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HOW TO MAKE A SLOW/FAST ROTATOR
FAST ROTATORS
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HOW TO MAKE A SLOW/FAST ROTATOR
FAST ROTATORS
Two fast rotator scenarios:
Time ->
Naab et al. 2014
Stellar mass
Stellar ang.
momentum
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HOW TO MAKE A SLOW/FAST ROTATOR
FAST ROTATORS
Two fast rotator scenarios:
Time ->
Stellar mass
Stellar ang.
momentum
Naab et al. 2014
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HOW TO MAKE A SLOW/FAST ROTATOR
FAST ROTATORS
Two slow rotator scenarios:
Time ->
Stellar mass
Stellar ang.
momentum
Naab et al. 2014
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Slow rotator:
1. Dispersion-dominated stars
2. Radiating hot gas, ‘maintained’ by
AGN feedback.
‘END’ STATES
Fast rotator:
1. Stellar rotation important!
2. Gas?
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WHAT IS THE GAS DOING IN FAST
ROTATORS?
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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
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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
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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
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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
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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
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GAS
Cold gas Cool gas Warm gas Hot gas
Expected, hot atmosphere of gas.
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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
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Should corotate with stars
Random rotation with respect to stars
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molecular gas stars
NGC 524
NGC 2768
co-rotation of gas
polar rotation of gas
Ψmol-star ≅ 0°
Ψmol-star ≅ 90°
GAS ORIGINS
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Cluster galaxies: almost all co-rotate
Field galaxies: only half co-rotate
Davis et al. 2011
GAS ORIGINS
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Davis et al. 2011
Cluster galaxies: very, very little external accretion
Field galaxies: about 50% of gas externally accreted
GAS ORIGINS
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Cluster galaxies: very, very little external accretion
Field galaxies: about 50% of gas externally accreted
GAS ORIGINS
Ongoing
external
accretion in HI
maps.
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cluster
non-cluster
But, cold gas detection fractions are the same in and out of the cluster…
GAS ORIGINS
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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
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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
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Cooling flow? Remnant from earlier spiral phase?
GAS ORIGINS
A galaxy suffering ram-
pressure stripping in the
Virgo cluster. (HST image)
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GAS ORIGINS
Cold gas Cool gas Warm gas Hot gas
What is fate of this gas?
Options:
1) Star formation
2) AGN feeding
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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
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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!
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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