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)

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

Powerful, short-lived, massive starbursts LBGs ?, BzKs ?, DRGs ? SMGs ? IEROs ? Hyper-EROs ? … ? Old, passively evolving, massive early-type galaxies z > 1.5-2z < 1-2 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 + FORS2 Large Program (145h; PI Cimatti) Target field : 50 arcmin 2 in the GOODS-South/HUDF region Sample selection : Spitzer+IRAC, m(4.5μm) 1.4 Sample size : N(m 1.4)= 390, 210 in 6 spectroscopic masks Ultradeep spectroscopy to B=27, I=26, 11h-30h integration 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 Spitzer VLT Arcetri

GMASS target field 51 arcmin 2 within the GOODS-South field covering a large fraction of the K20 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 Small contamination from objects with zphot > 1.4 and zspec < 1.4 z(phot) or z(spec) z(spec) (literature + GMASS) z(spec) (GMASS only) Spectroscopic redshift efficiency: red (12h-30h): ~70% (not final) blue (11h-15h): ~95%

Comparison with DRG selection

Spectra

J. Kurk

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

Multi-band SEDs

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

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 ( 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 micron ACS: b+v+i+z STACKING (3”x3”) Rodighiero et al.

Dusty z~2.5 ? Masses: 10^10-10^11 => SFR~1000 M_sun/yr 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 !