Using 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 arcmin 2, 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.
- Galaxies: elliptical and lenticular, cD
- Galaxies: evolution
- Galaxies: stellar content Online-only material: machine-readable tables
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science
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Ferreras, I. (Creator), Pasquali, A. (Creator), Malhotra, S. (Creator), Rhoads, J. (Creator), Cohen, S. (Creator), Windhorst, R. (Creator), Pirzkal, N. (Creator), Grogin, N. (Creator), Koekemoer, A. M. (Creator), Lisker, T. (Creator), Panagia, N. (Creator), Daddi, E. (Creator) & Hathi, N. P. (Creator), Centre de Donnees Strasbourg (CDS), 2012