Star Formation Downsizing: Testing the Role of Mergers and AGN

1. 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

2. 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

3. Introduction and Motivation: A Ride on the Downsizing Bandwagon

4. Bimodal Galaxy Distribution Star forming Blue Late type Young Passive Red Early type Old Bell et al. 2003 • Hubble Sequence - morphology shows dynamically distinct populations • Gas content/integrated colors - different ages and star formation histories

5. Bimodality & Mass z = 0 Early-type Old Late-type Young Kauffmann et al. 2003 Origin? Evolution?

6. … Dark Matter …

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

8. Downsizing: How to Build a Bandwagon

9. Downsizing: How to Build a Bandwagon Start with a broad prediction from confident theorists.

10. Downsizing: How to Build a Bandwagon Start with a broad prediction from confident theorists. Find observations that (you think) prove them wrong.

11. Downsizing: How to Build a Bandwagon • Start with a broad prediction from confident theorists. • Find observations that (you think) prove them wrong. • Existence of massive, evolved galaxies at z~2 (e.g. FIRES)

12. Downsizing: How to Build a Bandwagon • Start with a broad prediction from confident theorists. • 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)

13. Downsizing: How to Build a Bandwagon • Start with a broad prediction from confident theorists. • 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

14. Downsizing: How to Build a Bandwagon • Start with a broad prediction from confident theorists. • 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 Higher SFR Treu et al. 2005

15. Downsizing: How to Build a Bandwagon • Start with a broad prediction from confident theorists. • 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

16. Downsizing: How to Build a Bandwagon • Start with a broad prediction from confident theorists. • 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, …

17. Downsizing: How to Build a Bandwagon • Start with a broad prediction from confident theorists. • 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, … Juneau et al. 2005

18. Downsizing: How to Build a Bandwagon • Start with a broad prediction from confident theorists. • 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, … • Give it a catchy name.

19. Downsizing: Should We Be Worried?

20. Defining Downsizing • Archeological Downsizing • Age vs. mass at z=0 • Assembly Downsizing • Assembly rate vs. mass • Downsizing of Star Formation • SF/type vs. mass and redshift

21. 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.

22. 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.

23. How do we reconcile downsizing in the context of the hierarchical CDM paradigm?

24. Downsizing through Gastrophysics Mergers Starbursts/SN Cluster physics AGN Feedback

25. Downsizing through Gastrophysics Mergers Starbursts/SN Cluster physics AGN Feedback How do we understand mass and redshift dependence?

26. Observations: Characterizing Downsizing

27. 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 EGS 14:16 +52:00 Field 22 16:52 +34:00 Field 32 23:00 +00:00 Field 42 2:30 +00:00

28. Key Physical Properties • Stellar Mass • Palomar K-band, multi-band SED fitting • SFR Indicator (bimodality) • (U-B) Restframe Color, C. Willmer • Morphology (from GOODS, Bundy et al. 2005) • Environmental Density • 3rd nearest neighbor, M. Cooper

29. Results:Galaxy Stellar Mass Function Number Density • Little total evolution Mass

30. Results:Galaxy Stellar Mass Function Partitioned by restframe (U-B) color into blue (active) and red (quiescent) populations. Number Density • Little total evolution • Transformation to early-types Mass

31. Results:Galaxy Stellar Mass Function Partitioned by restframe (U-B) color into blue (active) and red (quiescent) populations. Number Density • Little total evolution • Transformation to early-types • Evolving transition mass, Mtr Mass

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

33. Red Fraction Growth Function 8% Gyr -1 Lowest M* 9% Gyr -1 Red Fraction 11% Gyr -1 16% Gyr -1 25% Gyr -1 Highest M* Cosmic Age (Gyr)

34. Is quenching and downsizing a result of environment?

35. Extreme Environments Low Density Mass

36. Extreme Environments Low Density Mass

37. Extreme Environments Low/High Density Mass

38. Extreme Environments Low/High Density • Moderate dependence on density • Downsizing accelerated in dense regions Mass

39. 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…

40. A Popular Picture Mergers Starbursts/SN Cluster physics AGN Feedback

41. A Popular Picture Mergers Starbursts/SN Cluster physics AGN Feedback

42. A Popular Picture Mergers Starbursts/SN Cluster physics AGN Feedback • Initial quenching of star formation (SF downsizing) and morphological transformation triggered by mergers. • Mergers also fuel black holes… may initiate radio mode AGN feedback.

43. Mergers & Feedback Springel, Hernquist, Hopkins

44. Is the picture correct? • We need to test the merger hypothesis. • We need to test the AGN hypothesis. • Connection to CDM halo assembly?

45. Testing the Current Picture: Are Major Mergers Enough?

46. Merge!

47. One Approach: Dynamical Mass Do New Spheroidals Form via Major Merging? (Astro-ph arXiv:0705:1007) 125 GOODS-N Spheroidals, 8 hr Keck spectra, IR Masses (Treu et al. 2005, Bundy et al. 2005)

48. What’s the strategy? Use dynamics to estimate Mvirial of halos hosting spheroidals. Compare to expected assembly history of dark matter halos.

49. Estimating Spheroidal Halo Mass Gavazzi et al. 2007 • 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. Virial Mass Stellar Mass

50. Spheroidal Halo Mass Function