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 Introduction and Motivation A Ride on the Downsizing Bandwagon. Observations: Characterizing Downsizing The 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 Bell et al Star forming Blue Late type Young Passive Red Early type Old Hubble Sequence - morphology shows dynamically distinct populations Gas content/integrated colors - different ages and star formation histories

Kauffmann et al Old Young Early-type Late-type z = 0 Origin? Evolution? Bimodality & Mass

… Dark Matter …

Hierarchical CDM Assembly z=18 z=6 z=1.4 z=0

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 Higher SFR

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 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 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 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 Formation SF/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 Formation SF/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 Mergers Cluster physics AGN Feedback Starbursts/SN

Downsizing through Gastrophysics 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 deg 2, R < 24.1 Spread over 4 fields, including the EGS Palomar K-band: 65 nights with WIRC on 200 inch 1.5 deg 2 to K=20, 0.2 deg 2 to K=21 Combined: 12,000 redshifts with K-band detections Field 22 16:52 +34:00Field 32 23:00 +00:00Field 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 ) 3. Environmental Density 3 rd nearest neighbor, M. Cooper

Results: Galaxy Stellar Mass Function Mass Number Density 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 Number Density

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, M tr Number Density

Red Fraction Growth Function Red Fraction Highest M * Lowest M * Cosmic Age (Gyr)

Red Fraction Growth Function Red Fraction 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 Mergers Cluster physics AGN Feedback Starbursts/SN

A Popular Picture Mergers Cluster physics AGN Feedback Starbursts/SN

A Popular 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.

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 M virial 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 Virial Mass Stellar Mass

Spheroidal Halo Mass Function

SDSS

Spheroidal Halo Mass Function SDSS New Spheroidals

Spheroidal Halo Mass Function New Spheroidals SDSS

Spheroidal Halo Mass Function Recent Halo 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, 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 AGN Hosts

AGN Host Mass Functions

Linking Quenching and AGN Quenching Rate

Linking Quenching and AGN

AGN Trigger Rate Assuming t AGN = 1 Gyr =  AGN /t AGN

Linking Quenching and AGN Set Quenching Rate equal to Trigger Rate

Linking Quenching and AGN Set Quenching Rate equal to Trigger Rate Hopkins Prediction (2005)

Evidence for a Link Nandra et al If t AGN ~ 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 t AGN ~ 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.