star formation downsizing: testing the role of mergers and agn
DESCRIPTION
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 Berkeley July, 2007. Outline. - PowerPoint PPT PresentationTRANSCRIPT
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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
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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
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Introduction and Motivation: A Ride on the Downsizing Bandwagon
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Bimodal Galaxy Distribution
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Bell et al. 2003
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QuickTime™ and aTIFF (Uncompressed) decompressor
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formingBlue
Late typeYoung
PassiveRed
Early typeOld
• Hubble Sequence - morphology shows dynamically distinct populations
• Gas content/integrated colors - different ages and star formation histories
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Kauffmann et al. 2003
Old
Young
Early-type
Late-type
z = 0
Origin?
Evolution?
Bimodality & MassQuickTime™ and a
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… Dark Matter …
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Hierarchical CDM Assembly
z=18
z=6
z=1.4
z=0
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Downsizing: How to Build a Bandwagon
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Downsizing: How to Build a Bandwagon
1. Start with a broad prediction from confident theorists.
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Downsizing: How to Build a Bandwagon
1. Start with a broad prediction from confident theorists.
2. Find observations that (you think) prove them wrong.
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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)
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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)
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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
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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
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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
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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, …
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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
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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.
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Downsizing: Should We Be Worried?
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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
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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.
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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.
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How do we reconcile downsizing in the context of the hierarchical CDM paradigm?
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Downsizing through Gastrophysics
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Mergers
Cluster physics
AGN Feedback
Starbursts/SN
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Downsizing through Gastrophysics
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Mergers
Cluster physics
AGN Feedback
Starbursts/SN
How do we understand mass and redshift dependence?
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Observations: Characterizing Downsizing
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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
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Field 22 16:52 +34:00 Field 32 23:00 +00:00 Field 42 2:30 +00:00
EGS 14:16 +52:00
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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
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Results:Galaxy
Stellar Mass Function
Mass
Nu
mb
er
Den
sity
• Little total evolution
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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
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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
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Red Fraction Growth Function
RedFraction
Highest M*
Lowest M*
Cosmic Age (Gyr)
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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
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Is quenching and downsizing a result of environment?
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Extreme Environments
Mass
Low Density
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Extreme Environments
Mass
Low Density
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Extreme Environments
Mass
Low/High Density
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Extreme Environments
Mass
• Moderate dependence on density
• Downsizing accelerated in dense regions
Low/High Density
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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…
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A Popular Picture
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Mergers
Cluster physics
AGN Feedback
Starbursts/SN
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A Popular Picture
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Mergers
Cluster physics
AGN Feedback
Starbursts/SN
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A Popular Picture
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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.
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Mergers & Feedback
Springel, Hernquist, Hopkins
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• We need to test the merger hypothesis.
• We need to test the AGN hypothesis.
• Connection to CDM halo assembly?
Is the picture correct?
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Testing the Current Picture: Are Major Mergers Enough?
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Merge!
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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)
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What’s the strategy?
Use dynamics to estimate Mvirial of halos hosting spheroidals.
Compare to expected assembly history of dark matter halos.
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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
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Spheroidal Halo Mass Function
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Spheroidal Halo Mass Function
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Spheroidal Halo Mass Function
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Spheroidal Halo Mass Function
SDSS
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Spheroidal Halo Mass Function
SDSS
New Spheroidals
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Spheroidal Halo Mass Function
New Spheroidals
SDSS
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Spheroidal Halo Mass Function
RecentHalo Mergers
Millennium Simulation
New Spheroidals
SDSS
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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?
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Testing the Current Picture: The Role of AGN Activity
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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.
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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?
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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)
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Key Questions
• Is there an observational link between evolution in AGN activity and star formation downsizing? Need M*
• Do AGNs cause quenching?
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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.
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AGN Host Mass Functions
AGNHosts
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AGN Host Mass Functions
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Linking Quenching and AGN
QuenchingRate
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Linking Quenching and AGN
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Linking Quenching and AGN
AGN TriggerRate
AssumingtAGN = 1 Gyr = AGN /tAGN
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Linking Quenching and AGN
Set QuenchingRate equal to Trigger
Rate
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Linking Quenching and AGN
Set QuenchingRate equal to Trigger
Rate
HopkinsPrediction
(2005)
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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)
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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?
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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.
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