Transcript GALAXY FORMATION AND EVOLUTION WITH K

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
McCarthy 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 ?, BzKs ?, 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 + 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
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 arcmin2 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
Spectroscopic redshift efficiency:
red (12h-30h): ~70% (not final)
blue (11h-15h): ~95%
z(phot) or z(spec)
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 + JH + 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”x3”)
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 !