1. Evidence for a Population of Massive Evolved Galaxies at z > 6.5 Bahram Mobasher M.Dickinson NOAO H. Ferguson STScI M. Giavalisco, M. Stiavelli STScI Alvio Renzini, Piero Rosati (ESO) T. Wiklind ESA/STScI R. S. Ellis (Caltech) D. Stark (Caltech), Nino Panagia M. Fall, A. Koekemoer (STScI)

2. It is generally accepted that galaxies we see today, form by mergers of smaller sub-units throughout the age of the Universe  Galaxies are younger and less massive at higher redshifts Is there NO massive and evolved system at high redshifts, when the Universe was < 1 Gyrs old ?  Only recently, with combined optical, near- Infrared and mid-Infrared observations one could explore this.

3. Balmer Break Technique for Selecting Massive and Old Galaxies at High redshifts

4. z = 7 no extinction t = 50 Myr t = 100 Myr t = 300 Myr t = 500 Myr t = 600 Myr t = 800 Myr The Balmer break is a prominent feature for stellar populations age t > 100 Myrs

5. H K 3.6  m J HK J dust-free post-starburst z ~ 7 dusty starburst z ~ 2.5 Dusty starburst at z ~ 2.5 Post starburst at z ~ 7 old Elliptical at z ~ 2.5

6. H K 3.6  m J HK J dust-free post-starburst z ~ 7 dusty starburst z ~ 2.5 Dusty starburst at z ~ 2.5 Post starburst at z ~ 7 old Elliptical at z ~ 2.5 Alternate way of selecting very high redshift candidates: Color-color selection:H - 3.6  m vs K - 3.6  m The slope of the short- side of the Balmer break is different for dusty starburst and dust-free post-starburst galaxies Avoids using J-band - often faint

9. Selecting Massive Evolved Galaxies at high-z - No detection at optical bands (BViz) - Red J-H colors (undetected in J-band) - Blue H-K ( i.e. flat H/K SED) - Red K- m 3.6 (K/IRAC(3.6  m) break) 18 galaxies found with 5 < z < 7 and stellar mass 8 x 10 10 – 5 x 10 11 M sun Wiklind et al (2006)

10. HUDF vs GOODS GOODS CDFS – 13 orbitsHUDF – 400 orbits

11. Discovery of an Extremely Massive and Evolved Galaxy at z ~ 6.5 Mobasher, B. et al ApJ 2005

12. further constraints - No detection at optical bands (BViz) to the HUDF limit at 2  level - J 110 - H 160 > 1.3 corresponding to the observed color of an LBG at z=8, taking into account IGM opacity

13. J-band dropout candidates in the HUDF no detection at optical bands close to slope unit line on H-3.6 vs. K-3.6 red K-3.6 color Selection criteria (Mobasher et al Ap.J 2005) (Mobasher et al 2005)

15. ACS

16. ACS+NICMOS+ISAAC

17. ACS+NICMOS+ISAAC+IRAC

19. B Vi z J H K IRAC B Vi z J H K

20. B Vi z J H K B Vi z J H K Bruzual and Charlot models (BC03) Starburst99 models (SB99) Simultaneously fitting: Redshift z Extinction E B-V Age, t Star formation history e-folding time  Metallicity Z

21. Summary of fitted parameters: High redshift, z = 6.5 Luminous, L BOL ~ 1 10 12 L o No extinction, E B-V = 0.0 No on-going star formation ‘Old’, age ~ 1 Gyr Very, very massive, M * ~ 5 10 11 M o

22. BC03Starburst99  2 vs. E B-V and redshift Best fit region covers : 6.0 < z < 7.7 Secondary fit for a dusty galaxy at z ~ 2.5 How stable is the solution? black :  2 minimum (1.9) white :  2 = 10

23. z=6.5 evolved Massive     Single burst  z  dusty  Starburst     Continous SFR  z  old  evolved   

25. Formation redshift (excluding those with ages > age of the universe) Results from Monte Carlo simulations: z = 6.5 E B-V = 0.0 Age = 600 Myr Z = 1.0 Z o M * = 4.6 10 11 M o z form ~ 10-15 median values A massive post-starburst galaxy at z ~ 7

27. Most frequently asked questions:

28. Could it be a dusty starburst at z~2 ?

29. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ?

30. z=6.5 evolved Massive     Single burst  z  dusty  Starburst     Continous SFR  z  old  evolved   

31. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ?

32. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ?

34. Mrk 231 BL QSO ULIRG

35. Mrk 231 + NGC 1608 highly obscured AGN

36. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ?

37. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ?

38. Gemini GNIRS spectroscopy of the z ~ 7 candidate: No lines detected Ly  ( 1216) z ~ 7 (0.97 micron) z ~ 0.8 - 1.2 J-band z ~ 1.3 - 1.8 H-band z ~ 2.0 - 2.8 K-band H  ( 6563)

39. No lines detected Ly  ( 1216) z ~ 7 (0.97 micron) z ~ 0.8 - 1.2 J-band z ~ 1.3 - 1.8 H-band z ~ 2.0 - 2.8 K-band H  ( 6563) In addition: Gemini-S GNIRS cross-dispersed VLT FORS HST ACS Grism Keck NIRSPEC Keck and VLT: sensitive to Ly  emission from galaxies at 6.8 < z < 8.0 with SFR 3-5 M o /yr Keck and Gemini: sensitive to H  emission from galaxies at 0.8 < z < 2.8 (with gaps) with line fluxes 1 10 -17 - 2 10 -18 erg cm -2 s -1

40. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ?

41. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ? Could it be gravitationally lensed ?

42. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ? Could it be gravitationally lensed ? Could it be a star ?

43. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ? Could it be gravitationally lensed ? Could it be a star ? how about other pop synthesis models ?

44. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ? Could it be gravitationally lensed ? Could it be a star ? how about other pop synthesis models ? different dust models ?

45. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ? Could it be gravitationally lensed ? Could it be a star ? how about other pop synthesis models ? different dust models ? Have you found more objects like this ?

46. Sample B J-band drop-out

47. z = 4.9 E B-V = 0.10 age = 700 Myr M * = 8 10 11 M o z = 7.2 E B-V = 0.05 age = 400 Myr M * = 4 10 11 M o z = 5.3 E B-V = 0.0 age = 300 Myr M * = 0.8 10 11 M o z = 7.2 E B-V = 0.0 age = 300 Myr M * = 2 10 11 M o Sample A massive post-starburst candidates

48. Sample A massive post-starburst candidates

50. Summary We present a technique for selecting very massive evolved galaxies at high redshift. This is based on combining deep optical/near-IR data with medium deep Spitzer observations An object is found in HUDF with an SED consistent with a post-starburst (evolved) galaxy with M =(2-5) x 10 11 M sun at z=6.-7.5. The object has undergone a single burst of SF and has an age of 1 Gyr.

51. Cont.. A less likely possibility is a very dusty evolved galaxy at z=2.5 with an age of ~600 Myrs. However, this produces a significantly worse fit to the observed SED. The low-z alternative requires the object to be detected in radio (1.4 GHz) or have spectral features indicative of SF. Our source has none of these.

52. Case against dusty post-starburst at low-z No detection of diagnostic spectral features in the spectra No radio detection If the 24 micron flux is due to PAH feature in a star-forming galaxy at z~2, we would have expected to detect this to the depth of our radio survey.

53. local galaxies m*>2.5E10 M O m*>1.0E11 M O EROs sub-mm K20 SDSS QSOs LBGs Somerville 2004

55. z = 7 no extinction t = 50 Myr t = 100 Myr t = 300 Myr t = 500 Myr t = 600 Myr t = 800 Myr The Balmer break is a prominent feature for stellar populations age t > 100 Myrs

56. z = 3 z = 4 z = 5 z = 6 z = 7

57. no extinction At z ~ 6 - 8 the Balmer break falls between the K-band and the IRAC 3.6 micron band At z ~ 6 - 8 the J-band is significantly fainter than K for ages of a few 100 Myrs t = 50 Myr t = 100 Myr t = 300 Myr t = 500 Myr t = 600 Myr t = 800 Myr

58. z = 7 no extinction t = 50 Myr t = 100 Myr t = 300 Myr t = 500 Myr t = 600 Myr t = 800 Myr At z ~ 6 - 8 the Balmer break falls between the K-band and the IRAC 3.6 micron band At z ~ 6 - 8 the J-band is significantly fainter than K for ages of a few 100 Myrs Selecting galaxies based on their K - 3.6  m and J - H colors would allow isolating very high redshift post-starburst galaxies Requires high quality near-infrared and Spitzer IRAC photometry This exists for the GOODS South field