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)

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.

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

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

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

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  m vs K  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

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 – 5 x M sun Wiklind et al (2006)

HUDF vs GOODS GOODS CDFS – 13 orbitsHUDF – 400 orbits

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

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

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)

ACS

ACS+NICMOS+ISAAC

ACS+NICMOS+ISAAC+IRAC

B Vi z J H K IRAC B Vi z J H K

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

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

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

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

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 * = M o z form ~ median values A massive post-starburst galaxy at z ~ 7

Most frequently asked questions:

Could it be a dusty starburst at z~2 ?

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

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

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

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 ?

Mrk 231 BL QSO ULIRG

Mrk NGC 1608 highly obscured AGN

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 ?

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 ?

Gemini GNIRS spectroscopy of the z ~ 7 candidate: No lines detected Ly  ( 1216) z ~ 7 (0.97 micron) z ~ J-band z ~ H-band z ~ K-band H  ( 6563)

No lines detected Ly  ( 1216) z ~ 7 (0.97 micron) z ~ J-band z ~ H-band z ~ 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 erg cm -2 s -1

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 ?

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 ?

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 ?

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 ?

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 ?

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 ?

Sample B J-band drop-out

z = 4.9 E B-V = 0.10 age = 700 Myr M * = M o z = 7.2 E B-V = 0.05 age = 400 Myr M * = M o z = 5.3 E B-V = 0.0 age = 300 Myr M * = M o z = 7.2 E B-V = 0.0 age = 300 Myr M * = M o Sample A massive post-starburst candidates

Sample A massive post-starburst candidates

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 M sun at z= The object has undergone a single burst of SF and has an age of 1 Gyr.

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.

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.

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

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

z = 3 z = 4 z = 5 z = 6 z = 7

no extinction At z ~ the Balmer break falls between the K-band and the IRAC 3.6 micron band At z ~ 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

z = 7 no extinction t = 50 Myr t = 100 Myr t = 300 Myr t = 500 Myr t = 600 Myr t = 800 Myr At z ~ the Balmer break falls between the K-band and the IRAC 3.6 micron band At z ~ the J-band is significantly fainter than K for ages of a few 100 Myrs Selecting galaxies based on their K  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