Evidence for a Population of Massive Evolved Galaxies at z > 6.5

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

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

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

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(3.6mm) break) 18 galaxies found with 5 < z < 7 and stellar mass 8 x 1010 – 5 x 1011 Msun Wiklind et al (2006)

10. HUDF vs GOODS GOODS CDFS – 13 orbits HUDF – 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 2s level J110 - H160 > 1.3 corresponding to the observed color of an LBG at z=8, taking into account IGM opacity

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

15. ACS

16. ACS+NICMOS+ISAAC

17. ACS+NICMOS+ISAAC+IRAC

19. K K H H IRAC J J z z B B V V i i

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

21. Summary of fitted parameters: • High redshift, z = 6.5 • Luminous, LBOL ~ 1 1012 Lo • No extinction, EB-V = 0.0 • No on-going star formation • ‘Old’, age ~ 1 Gyr • Very, very massive, M* ~ 5 1011 Mo

22. c2 vs. EB-V and redshift BC03 Starburst99 Best fit region covers : 6.0 < z < 7.7 Secondary fit for a dusty galaxy at z ~ 2.5 black : c2 minimum (1.9) white : c2 = 10 How stable is the solution?

23. z=6.5 evolved Massive c2n = 1.8 Single burst z=2.5 dusty Starburst c2n=6.7 Continous SFR z=3.4 old evolved c2n=29.9

25. Formation redshift (excluding those with ages > age of the universe) Results from Monte Carlo simulations: • z = 6.5 • EB-V = 0.0 • Age = 600 Myr • Z = 1.0 Zo • M* = 4.6 1011 Mo • zform ~ 10-15 median values A massive post-starburst galaxy at z ~ 7

27. Most frequently asked questions:

28. Most frequently asked questions: 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 c2n = 1.8 Single burst z=2.5 dusty Starburst c2n=6.7 Continous SFR z=3.4 old evolved c2n=29.9

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 z ~ 0.8 - 1.2 J-band z ~ 1.3 - 1.8 H-band z ~ 2.0 - 2.8 K-band Lya (l1216) z ~ 7 (0.97 micron) Ha (l6563)

39. In addition: • Gemini-S GNIRS cross-dispersed • VLT FORS • HST ACS Grism • Keck NIRSPEC Keck and VLT: sensitive to Lya emission from galaxies at 6.8 < z < 8.0 with SFR 3-5 Mo/yr No lines detected z ~ 0.8 - 1.2 J-band z ~ 1.3 - 1.8 H-band z ~ 2.0 - 2.8 K-band Keck and Gemini: sensitive to Ha 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 Lya (l1216) z ~ 7 (0.97 micron) Ha (l6563)

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. Sample A massive post-starburst candidates z = 4.9 EB-V = 0.10 age = 700 Myr M* = 8 1011 Mo z = 7.2 EB-V = 0.05 age = 400 Myr M* = 4 1011 Mo z = 5.3 EB-V = 0.0 age = 300 Myr M* = 0.8 1011 Mo z = 7.2 EB-V = 0.0 age = 300 Myr M* = 2 1011 Mo

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 1011 Msun at z=6.-7.5. The object has undergone a single burst of SF and has an age of 1 Gyr.