Star Formation Downsizing:Testing the Role of Mergers and AGN
Kevin Bundy(University of Toronto)
Richard Ellis (Caltech), Tommaso Treu (UCSB),
Antonis Georgakakis, Paul Nandra, Elise Laird (IC)
DEEP2 Team at UC Berkeley & Santa Cruz
UC BerkeleyJuly, 2007
Outline
• Introduction and MotivationA Ride on the Downsizing Bandwagon.
• Observations: Characterizing DownsizingThe quenching of star formation, the rise of early-
types.
• Are Major Mergers Enough?
• The Role of AGN Activity
Introduction and Motivation: A Ride on the Downsizing Bandwagon
Bimodal Galaxy Distribution
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Bell et al. 2003
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.QuickTime™ and a
TIFF (Uncompressed) decompressorare needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.Star
formingBlue
Late typeYoung
PassiveRed
Early typeOld
• Hubble Sequence - morphology shows dynamically distinct populations
• Gas content/integrated colors - different ages and star formation histories
Kauffmann et al. 2003
Old
Young
Early-type
Late-type
z = 0
Origin?
Evolution?
Bimodality & MassQuickTime™ and a
TIFF (Uncompressed) decompressorare needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
… Dark Matter …
Hierarchical CDM Assembly
z=18
z=6
z=1.4
z=0
Downsizing: How to Build a Bandwagon
Downsizing: How to Build a Bandwagon
1. Start with a broad prediction from confident theorists.
Downsizing: How to Build a Bandwagon
1. Start with a broad prediction from confident theorists.
2. Find observations that (you think) prove them wrong.
Downsizing: How to Build a Bandwagon
1. Start with a broad prediction from confident theorists.
2. Find observations that (you think) prove them wrong.
• Existence of massive, evolved galaxies at z~2 (e.g. FIRES)
Downsizing: How to Build a Bandwagon
1. Start with a broad prediction from confident theorists.
2. Find observations that (you think) prove them wrong.
• Existence of massive, evolved galaxies at z~2 (e.g. FIRES)
• The most massive galaxies at z=0 have the oldest stellar pops (many examples, see Heavens et al. 2004)
Downsizing: How to Build a Bandwagon
1. Start with a broad prediction from confident theorists.
2. Find observations that (you think) prove them wrong.
• Existence of massive, evolved galaxies at z~2 (e.g. FIRES)
• The most massive galaxies at z=0 have the oldest stellar pops (many examples, see Heavens et al. 2004)
• Evolution in M/L from the Fundamental Plane
1. Start with a broad prediction from confident theorists.
2. Find observations that (you think) prove them wrong.
• Existence of massive, evolved galaxies at z~2 (e.g. FIRES)
• The most massive galaxies at z=0 have the oldest stellar pops (many examples, but see Heavens et al. 2004)
• Evolution in M/L from the Fundamental Plane
Downsizing: How to Build a Bandwagon
Treu et al. 2005
HigherSFR
Downsizing: How to Build a Bandwagon
1. Start with a broad prediction from confident theorists.
2. Find observations that (you think) prove them wrong.
• Existence of massive, evolved galaxies at z~2 (e.g. FIRES)
• The most massive galaxies at z=0 have the oldest stellar pops (many examples, see Heavens et al. 2004)
• Evolution in M/L from the Fundamental Plane
Downsizing: How to Build a Bandwagon
1. Start with a broad prediction from confident theorists.
2. Find observations that (you think) prove them wrong.
• Existence of massive, evolved galaxies at z~2 (e.g. FIRES)
• The most massive galaxies at z=0 have the oldest stellar pops (many examples, see Heavens et al. 2004)
• Evolution in M/L from the Fundamental Plane
• Surveys: Cowie et al. 1996, Brinchmann & Ellis 2000, Bell et al. 2005 COMBO17, Bauer et al. 2005, Juneau et al. 2005, Borsch et al. 2006, Brown et al. 2006, …
1. Start with a broad prediction from confident theorists.
2. Find observations that (you think) prove them wrong.
• Existence of massive, evolved galaxies at z~2 (e.g. FIRES)
• The most massive galaxies at z=0 have the oldest stellar pops (many examples, see Heavens et al. 2004)
• Evolution in M/L from the Fundamental Plane
• Surveys: Cowie et al. 1996, Brinchmann & Ellis 2000, Bell et al. 2005 COMBO17, Bauer et al. 2005, Juneau et al. 2005, Borsch et al. 2006, Brown et al. 2006, …
Downsizing: How to Build a Bandwagon
Juneau et al. 2005
Downsizing: How to Build a Bandwagon
1. Start with a broad prediction from confident theorists.
2. Find observations that (you think) prove them wrong.
• Existence of massive, evolved galaxies at z~2 (e.g. FIRES)
• The most massive galaxies at z=0 have the oldest stellar pops (many examples, see Heavens et al. 2004)
• Evolution in M/L from the Fundamental Plane
• Surveys: Cowie et al. 1996, Brinchmann & Ellis 2000, Bell et al. 2005 COMBO17, Bauer et al. 2005, Juneau et al. 2005, Borsch et al. 2006, Brown et al. 2006, …
3. Give it a catchy name.
Downsizing: Should We Be Worried?
Defining Downsizing
1. Archeological Downsizing
• Age vs. mass at z=0
2. Assembly Downsizing
• Assembly rate vs. mass
3. Downsizing of Star Formation
• SF/type vs. mass and redshift
3. Downsizing of Star FormationSF/type vs. mass and redshift
The sites of star formation appear to shift from including high-mass galaxies at early epochs (z~1-2) to only lower-mass galaxies at later epochs.
3. Downsizing of Star FormationSF/type vs. mass and redshift
The sites of star formation appear to shift from including high-mass galaxies at early epochs (z~1-2) to only lower-mass galaxies at later epochs.
How do we reconcile downsizing in the context of the hierarchical CDM paradigm?
Downsizing through Gastrophysics
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Mergers
Cluster physics
AGN Feedback
Starbursts/SN
Downsizing through Gastrophysics
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Mergers
Cluster physics
AGN Feedback
Starbursts/SN
How do we understand mass and redshift dependence?
Observations: Characterizing Downsizing
The Palomar K-band + DEEP2 Redshift Survey
• DEEP2: 40,000 spec-z’s from DEIMOS on Keck II
80 Keck nights, z<1.5 over 3 deg2, R < 24.1
Spread over 4 fields, including the EGS
• Palomar K-band: 65 nights with WIRC on 200 inch
1.5 deg2 to K=20, 0.2 deg2 to K=21
• Combined: 12,000 redshifts with K-band detections
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.
Field 22 16:52 +34:00 Field 32 23:00 +00:00 Field 42 2:30 +00:00
EGS 14:16 +52:00
Key Physical Properties
1. Stellar Mass
• Palomar K-band, multi-band SED fitting
2. SFR Indicator (bimodality)
• (U-B) Restframe Color, C. Willmer
• Morphology (from GOODS, Bundy et al. 2005)
3. Environmental Density
• 3rd nearest neighbor, M. Cooper
Results:Galaxy
Stellar Mass Function
Mass
Nu
mb
er
Den
sity
• Little total evolution
Results:Galaxy
Stellar Mass Function
Partitioned by restframe (U-B) color into blue
(active) and red (quiescent) populations.
Mass
• Little total evolution
• Transformation to early-types
Nu
mb
er
Den
sity
Results:Galaxy
Stellar Mass Function
Partitioned by restframe (U-B) color into blue
(active) and red (quiescent) populations.
Mass
• Little total evolution
• Transformation to early-types
• Evolving transition mass, Mtr
Nu
mb
er
Den
sity
Red Fraction Growth Function
RedFraction
Highest M*
Lowest M*
Cosmic Age (Gyr)
Red Fraction Growth Function
RedFraction
Highest M*
Lowest M*
Cosmic Age (Gyr)
8% Gyr -1
9% Gyr -1
11% Gyr -1
16% Gyr -1
25% Gyr -1
Is quenching and downsizing a result of environment?
Extreme Environments
Mass
Low Density
Extreme Environments
Mass
Low Density
Extreme Environments
Mass
Low/High Density
Extreme Environments
Mass
• Moderate dependence on density
• Downsizing accelerated in dense regions
Low/High Density
What Have We Learned?
• Downsizing results from the quenching of star formation.
• Quenching is accelerated in dense environments but is apparent in all environments.
• We are therefore looking for internal (non-environmental) processes…
A Popular Picture
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Mergers
Cluster physics
AGN Feedback
Starbursts/SN
A Popular Picture
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Mergers
Cluster physics
AGN Feedback
Starbursts/SN
A Popular Picture
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Mergers
Cluster physics
AGN Feedback
Starbursts/SN
• Initial quenching of star formation (SF downsizing) and morphological transformation triggered by mergers.
• Mergers also fuel black holes… may initiate radio mode AGN feedback.
QuickTime™ and a decompressor
are needed to see this picture.
Mergers & Feedback
Springel, Hernquist, Hopkins
• We need to test the merger hypothesis.
• We need to test the AGN hypothesis.
• Connection to CDM halo assembly?
Is the picture correct?
Testing the Current Picture: Are Major Mergers Enough?
Merge!
One Approach: Dynamical Mass
125 GOODS-N Spheroidals, 8 hr Keck spectra, IR Masses(Treu et al. 2005, Bundy et al. 2005)
Do New Spheroidals Form via Major Merging?
(Astro-ph arXiv:0705:1007)
What’s the strategy?
Use dynamics to estimate Mvirial of halos hosting spheroidals.
Compare to expected assembly history of dark matter halos.
Estimating Spheroidal Halo Mass
• Assume simple isothermal+NFW profile motivated by lensing results.
• Normalization set by 2
Calibrate to M* in two z-bins and apply to the full GOODS spheroidal sample.
Gavazzi et al. 2007
Vir
ial
Mass
Stellar Mass
Spheroidal Halo Mass Function
Spheroidal Halo Mass Function
Spheroidal Halo Mass Function
Spheroidal Halo Mass Function
SDSS
Spheroidal Halo Mass Function
SDSS
New Spheroidals
Spheroidal Halo Mass Function
New Spheroidals
SDSS
Spheroidal Halo Mass Function
RecentHalo Mergers
Millennium Simulation
New Spheroidals
SDSS
What this tells us
• Apparently not enough major mergers to support rising abundance of spheroidals… !
• Other mechanisms involved: secular bulge growth, disk fading, role of S0 galaxies. (see Bower; DeLucia; Lotz)
• What about AGN/starburst feedback and M- relation?
Testing the Current Picture: The Role of AGN Activity
The Appeal of AGN• Widely recognized presence of SM black holes and
the M•- relation.
• Large available energy without need for SF.
• Cluster cooling flows.
• AGN “Downsizing” in Luminosity Function (e.g., Barger et al. 2005)
• Observations beginning to link AGN hosts with red early-types and post-starbursts. (Kauffmann et al. 2004, Grogin et al. 2005, Nandra et al. 2007, Pierce et al. 2007, Yan et al. 2006, Goto et al. 2006)
There are (at least) 2 ideas of how AGN feedback works.
Merger-Driven, Explosive Feedback
Springel, Hernquist, Hopkins, Robertson, Di Matteo
• Importance of merging... morphological transformation.
• What sets the mass dependence?
• What prevents gas from cooling and forming stars later?
• Can starbursts do the same thing? How would you tell?
Radio Mode AGN Feedback
• Halo gas pre-heated… how?
• Low AGN luminosity, but efficient coupling to hot gas.
• Now implemented in many semi-analytic models. (Granato et al. 2004, Croton et al. 2006, Bower et al. 2006, Scannapieco et al. 2005)
Key Questions
• Is there an observational link between evolution in AGN activity and star formation downsizing? Need M*
• Do AGNs cause quenching?
Chandra X-ray Observations from AEGIS
• 200 ks, covering the EGS, 0.5-10 keV, 1300 sources
• 170 X-ray sources with redshifts and K-band masses
• Primarily selects obscured AGN hosts, some QSOs
• ~50% more could be X-ray absorbed.
AGN Host Mass Functions
AGNHosts
AGN Host Mass Functions
Linking Quenching and AGN
QuenchingRate
Linking Quenching and AGN
Linking Quenching and AGN
AGN TriggerRate
AssumingtAGN = 1 Gyr = AGN /tAGN
Linking Quenching and AGN
Set QuenchingRate equal to Trigger
Rate
Linking Quenching and AGN
Set QuenchingRate equal to Trigger
Rate
HopkinsPrediction
(2005)
Evidence for a Link
Nandra et al. 2006
• If tAGN ~ Gyr, X-ray luminous AGN are likely to be associated with quenching.
• AGN hosts are mostly red, early-type, possibly post-starburst. (e.g., Yan et al. 2006, Nandra et al. 2007, Pierce et al. 2007, Grogin et al. 2005, Kauffmann et al. 2004)
Evidence for a Link
• If tAGN ~ Gyr, X-ray luminous AGN are likely to be associated with quenching.
• AGN hosts are mostly red, early-type, possibly post-starburst. (e.g., Yan et al. 2006, Nandra et al. 2007, Pierce et al. 2007, Grogin et al. 2005, Kauffmann et al. 2004)
• But estimated accretion rates show a large dispersion in both host mass and color, suggesting AGNs do not cause quenching. Refueling?
Summary and Conclusions
• Quenching of star formation leads to downsizing which is apparent in all environments, suggesting non-environmental mechanisms are important.
• Major mergers, however, may not be enough to explain the rising abundance of spheroidals.
• New evidence links mass dependent AGN activity with quenching, but argues against the notion that explosive AGN feedback causes quenching to occur.
Top Related