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. 2005Bundy et al. 2006

Cimatti et al. 2004McCarthy et al. 2004Saracco et al. 2005Daddi et al. 2005

Powerful, short-lived,massive starbursts

LBGs ?, BzKs ?, DRGs ? SMGs ? IEROs ? Hyper-EROs ? … ?

Old, passivelyevolving, massiveearly-type galaxies

z > 1.5-2 z < 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 arcmin2 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, 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 arcmin2 within theGOODS-South fieldcovering a large fraction of the K20 andHubble 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

1.6μmbump

Preliminary redshift statistics

Small contamination from objectswith 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=35M. Mignoli

Multi-band SEDs

Photometric SED fitting with known z(spec)

UBVRIz + BViz + JH + JHKs + IRAC

Bolzonella, Pozzetti

Stellar mass estimates

zspeczphot

Main properties

Passive or weakly star-formingOld stars (1-3 Gyr)Massive (log M_stars = 10.9 – 11.2 Msun, Chabrier IMF)Low levels of specific SFR Early-type morphology

Star-formingLow 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 extinctionHigh specific star formationSolar metallicity from UV photospheric features (Halliday et al.)Strong morphological K-correctionStar 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

ACS: b+v+i+z

STACKING (3”x3”)

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 leadingto the formation and mass assembly of massive early-type galaxies

In the redshift range of 1.5 < z < 3, GMASS is unveiling co-existingpopulations of old, passive, massive early-type galaxies up to z~2and massive starbursts probably experiencing their dominant phaseof 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 !