Early-type galaxies in the pears survey: Probing the stellar populations at moderate redshift

Ignacio Ferreras, Anna Pasquali, Sangeeta Malhotra, James Rhoads, Seth Cohen, Rogier Windhorst, Nor Pirzkal, Norman Grogin, Anton M. Koekemoer, Thorsten Lisker, Nino Panagia, Emanuele Daddi, Nimish P. Hathi

Research output: Contribution to journalArticlepeer-review

43 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)158-169
Number of pages12
JournalAstrophysical Journal
Issue number1
StatePublished - 2009


  • 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


Dive into the research topics of 'Early-type galaxies in the pears survey: Probing the stellar populations at moderate redshift'. Together they form a unique fingerprint.

Cite this