Ignacio Ferreras et al. 2009 ApJ 706 158 doi:10.1088/0004-637X/706/1/158
EARLY-TYPE GALAXIES IN THE PEARS SURVEY: PROBING THE STELLAR POPULATIONS AT MODERATE REDSHIFT
FREE ISSUEIgnacio Ferreras1, Anna Pasquali2, Sangeeta Malhotra3, James Rhoads3, Seth Cohen3, Rogier Windhorst3, Nor Pirzkal4, Norman Grogin4, Anton M. Koekemoer4, Thorsten Lisker5, Nino Panagia4, Emanuele Daddi6 and Nimish P. Hathi7
Show affiliationsUsing Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) slitless grism spectra from the PEARS program, we study the stellar populations of morphologically selected early-type galaxies in the GOODS North and South fields. The sample—extracted from a visual classification of the (v2.0) HST/ACS images and restricted to redshifts z > 0.4—comprises 228 galaxies (i F775W < 24 mag, AB) out to z 
1.3 over 320 arcmin2, with a median redshift z M = 0.75. This work significantly increases our previous sample from the GRAPES survey in the HUDF (18 galaxies over ~11 arcmin2). The grism data allow us to separate the sample into "red" and "blue" spectra, with the latter comprising 15% of the total. Three different grids of models parameterizing the star formation history are used to fit the low-resolution spectra. Over the redshift range of the sample—corresponding to a cosmic age between 5 and 10 Gyr—we find a strong correlation between stellar mass and average age, whereas the spread of ages (defined by the root mean square of the distribution) is roughly ~1 Gyr and independent of stellar mass. The best-fit parameters suggest that it is the formation epoch and not the formation timescale that best correlates with mass in early-type galaxies. This result—along with the recently observed lack of evolution of the number density of massive galaxies—motivates the need for a channel of (massive) galaxy formation bypassing any phase in the blue cloud, as suggested by the simulations of Dekel et al.
- Keywords
galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: stellar content
- Dates
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Issue 1 (2009 November 20)
Received 2009 March 31, accepted for publication 2009 October 6
Published 2009 October 28
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Early-Type Galaxies in the PEARS Survey: Probing the Stellar Populations at Moderate Redshift
Ignacio Ferreras et al. 2009 ApJ 706 158
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