Journal Article

Star formation histories and evolution of the 35 brightest E+A galaxies from the Sloan Digital Sky Survey Data Release 5

W. Du, A. L. Luo, Ph. Prugniel, Y. C. Liang and Y. H. Zhao

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 409, issue 2, pages 567-581
Published in print December 2010 | ISSN: 0035-8711
Published online November 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17413.x
Star formation histories and evolution of the 35 brightest E+A galaxies from the Sloan Digital Sky Survey Data Release 5

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For our sample, we have selected the 35 brightest galaxies from the Goto E+A galaxy catalogue, taken from the Sloan Digital Sky Survey Data Release 5. As E+A galaxies have experienced starburst recently and quenched it abruptly, these are considered as post-starburst galaxies. The spectra of E+A galaxies are prominently characterized by strong Balmer absorption lines but few [O ii] or Hα emission lines. In this paper we study the stellar populations of our E+A sample by fitting their spectra using ulyss, which is a robust full-spectrum fitting method. We fit each galaxy of the sample with one-population – a single stellar population (SSP) – and three-population (three SSPs) models, separately. Using one-population fits, we obtain SSP equivalent ages and metallicities, which correspond to ‘luminosity-weighted’ averages. Using three-population fits, we divide the stellar components of a galaxy into three groups by age: old stellar population (OSP), intermediate-age stellar population (ISP) and young stellar population (YSP). We then derive the optimal age, metallicity and population fractions in both mass and luminosity of OSP, ISP and YSP for each galaxy of the E+A sample. During the fits, both Pegase.HR/Elodie3.1 and Vazdekis/Miles are used as two independent stellar population models. The two models result in generally consistent conclusions as follows. For all of the E+A samples, YSPs (≤1 Gyr) make important contributions to the luminosity. However, the dominant contributors to the mass are OSPs. We also reconstruct the smoothing star formation history for each galaxy of the E+A sample by giving the star formation rate (SFR) versus the evolutionary age. All of the E+A samples have low SFRs in the intermediate evolutionary stage. 11 of the 35 E+A galaxies have high SFRs in the early evolutionary stage. However, another 11 have SFRs that are high during the late evolutionary stage. This might be a result of the recently occurred but abruptly truncated starburst in such galaxies. In addition, we fit the E+A sample and 34 randomly selected elliptical galaxies with two-population (two SSPs) model, which divides the stellar components of a galaxy into two groups by age (old and young components). We obtain the equivalent age of the old component for each galaxy of the E+A sample and elliptical galaxies. By comparison, the old components of E+A galaxies are statistically much younger than those of ellipticals. From the standpoint of the stellar population age, this probably provides evidence for the proposed evolutionary link from E+A galaxies to early-type galaxies (E/S0s).

Keywords: galaxies: evolution; galaxies: general; galaxies: star formation; galaxies: stellar content

Journal Article.  10809 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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