Searching for massive galaxy progenitors with GMASS
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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)
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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
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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
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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
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GMASS target field
51 arcmin2 within theGOODS-South fieldcovering a large fraction of the K20 andHubble Ultra Deep Field (UDF) areas
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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
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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%
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Comparison with DRG selection
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Spectra
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J. Kurk
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Average spectrum of first blue mask objects
N=35M. Mignoli
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Multi-band SEDs
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Photometric SED fitting with known z(spec)
UBVRIz + BViz + JH + JHKs + IRAC
Bolzonella, Pozzetti
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Stellar mass estimates
zspeczphot
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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 ?
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Beyond GMASS …
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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.
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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
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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 ?
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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 !