Searching for massive galaxy progenitors with GMASS Galaxy

Searching for massive galaxy progenitors with GMASS (Galaxy Mass Assembly ultradeep Spectroscopic Survey) (a progress report) Andrea Cimatti (INAF-Arcetri) M. Bolzonella (INAF-Bologna), P. Cassata (INAF-Milano), E. Daddi (NOAO), M. Dickinson (NOAO), A. Franceschini (Uni-Padova), C. Halliday (INAF-Arcetri), J. Kurk (MPIA), C. Mancini (Uni-Firenze), M. Mignoli (INAF-Bologna), L. Pozzetti (INAF-Bologna), A. Renzini (INAF-Padova), G. Rodighiero (Uni-Padova), P. Rosati (ESO), G. Zamorani (INAF-Bologna)

The emerging picture z~0 0<z<1 1<z<2 Cimatti et al. 2004 Mc. Carthy et al. 2004 Saracco et al. 2005 Daddi et al. 2005 Thomas et al. 2005 Bundy et al. 2006 “Downsizing” evolutionary pattern (Cowie et al. 1996) (supported by several other results, e. g. FP, SSFR, …)

z > 1. 5 -2 Powerful, short-lived, massive starbursts z < 1 -2 ? Old, passively evolving, massive early-type galaxies LBGs ? , Bz. Ks ? , DRGs ? SMGs ? IEROs ? Hyper-EROs ? … ? GMASS Search for the highest redshift ETGs Identify and study the progenitors of massive ETGs Stellar mass assembly evolution at 1. 5<z<3

GMASS main features ESO VLT + FORS 2 Large Program (145 h; PI Cimatti) Target field : 50 arcmin 2 in the GOODS-South/HUDF region Sample selection : Spitzer+IRAC, m(4. 5μm) < 23 (AB) + z(phot) > 1. 4 Sample size : N(m<23)= 1190, N(zphot>1. 4)= 390 , 210 in 6 spectroscopic masks Ultradeep spectroscopy to B=27, I=26, 11 h-30 h integration Spitzer Complementary to other surveys (depth, no color selections) 100% of data taken in service mode up to 31 December 2005 (80% reduced) Reduced and calibrated data will be publicly available worldwide VLT Arcetri

GMASS target field 51 arcmin 2 within the GOODS-South field covering a large fraction of the K 20 and Hubble Ultra Deep Field (UDF) areas

Why 4. 5µm selection ? Best compromise among IRAC bands (sensitivity, PSF, IQ, blending) “Negative” k-correction (the stellar SED peak enters the 4. 5μm-band for z>1. 5) Better sensitivity to stellar mass up to z~3 Less affected by dust extinction than K-band 1. 6μm bump

Preliminary redshift statistics Spectroscopic redshift efficiency: red (12 h-30 h): ~70% (not final) blue (11 h-15 h): ~95% z(phot) or z(spec) (literature + GMASS) z(spec) (GMASS only) Small contamination from objects with zphot > 1. 4 and zspec < 1. 4

Comparison with DRG selection

Spectra

J. Kurk

Average spectrum of first blue mask objects M. Mignoli N=35

Multi-band SEDs

Photometric SED fitting with known z(spec) Bolzonella, Pozzetti UBVRIz + BViz + JHKs + IRAC

Stellar mass estimates zspec zphot

Main properties Passive or weakly star-forming Old stars (1 -3 Gyr) Massive (log M_stars = 10. 9 – 11. 2 Msun, Chabrier IMF) Low levels of specific SFR Early-type morphology Star-forming Low mass blue systems (log M_stars ~ 10 Msun) Red systems with large mass (log M_stars ~ 11+) and strong star formation (50 -100 Msun/yr) Red more because of age than dust extinction High specific star formation Solar metallicity from UV photospheric features (Halliday et al. ) Strong morphological K-correction Star formation located mostly in outer regions “Transition” phase leading to an old/massive ETG ?

Beyond GMASS …

Optical blank-fields + extremely K-band faint (K[AB]<25) z J H K 3. 6 4. 5 5. 8 8. 0 24 micron STACKING (3”x 3”) ACS: b+v+i+z Rodighiero et al.

Dusty Starbursts @ z~2. 5 ? Masses: 10^10 -10^11 => SFR~1000 M_sun/yr Post-starbursts @ z~6. 5 ? Masses: 10^11 -10^12 + AGN (Mobasher et al. 2006) Superantennae +Av=3 Dusty Torus

Mid-Infrared colours: the bulk of the sources are consistent with a population of starbursts at z~2 -3 Are we looking at a mixed population ?

Short summary GMASS is designed to investigate the physical mechanisms leading to the formation and mass assembly of massive early-type galaxies In the redshift range of 1. 5 < z < 3, GMASS is unveiling co-existing populations of old, passive, massive early-type galaxies up to z~2 and massive starbursts probably experiencing their dominant phase of star formation and mass assembly Population of IRAC galaxies with no optical and sometimes near-IR counterparts: old systems + AGN at z>6 or extreme dusty starbursts ? Have a look at Claire Halliday’s and Jaron Kurk’s posters and STAY TUNED !