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Astron. Astrophys. 328, 499-509 (1997)

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Evolution of quasar absorption-selected galaxies *

P. Guillemin 1 and J. Bergeron 2, 1

1 Institut d'Astrophysique de Paris, CNRS, 98bis Boulevard Arago, F-75014 Paris, France
2 European Southern Observatory, Karl-Schwarzschild Stra [FORMULA] e 2, D-85748 Garching bei München, Germany

Received 19 August 1996 / Accepted 27 May 1997

Abstract

We present the results of a survey of galaxies selected by their gas cross-section which give rise to Mg II absorption lines in the spectra of background quasars. The sample comprises 11 galaxies covering the redshift range [FORMULA] with [FORMULA] =0.9, and is combined with a lower redshift ([FORMULA]) sample of 15 Mg II absorbing galaxies. We first describe the properties of these two samples of galaxies whose spectra range from present-day elliptical to irregular galaxies with a dominance of Sbc and Scd types. The strong correlation found previously at lower redshift between the halo radius and the galaxy luminosity still holds at [FORMULA], which implies no significant evolution in redshift of the gaseous halo sizes. We find no evidence of a correlation between the rest-frame equivalent width of the [O II ] [FORMULA] emission line and the rest-frame luminosity [FORMULA] (B). This could be a consequence of the very blue B-K color of intrinsically faint absorbing galaxies in the infrared, thus optically bright as found in other surveys. For the low and high redshift ([FORMULA]) samples, we have built template spectra by combining individual galaxy spectra. The lack of detection of the [N II ] emission line in the low-redshift template, [N II ] [FORMULA] 6568/H [FORMULA] 0.2, together with the values obtained for empirical abundance indicators, suggests a O/H abundance in the disk of Mg II absorbing galaxies in the range [O/H]= [FORMULA]. The spectral energy distribution (SED) of these templates at [FORMULA] 3646Å can be fitted by present-day Sbc or Sc galaxies, but the UV excess at [FORMULA] 3500Å follows the SED of Scd and Im present-day galaxies at [FORMULA] =0.4 and 0.9 respectively. This blueing of the SED with redshift is associated with an increase of [FORMULA] ([O II ] [FORMULA]) by about 45%. To investigate the past history of star formation of the Mg II absorbing galaxies, we have used the spectral evolution models of stellar populations developed by Bruzual & Charlot as well as red and blue absorber subsamples (individual galaxies with a Ba + Ca II break [FORMULA]). The red subtemplates are well fitted by a Sb galaxy and the derived ages, 4.5 and 8.3 Gyr at z =0.9 and 0.4 respectively, implies a similar galaxy formation epoch for the [FORMULA] =0.4 and 0.9 Mg II absorbing galaxies. Results for the blue subtemplates using Sc galaxy models, especially that at [FORMULA] =0.9, suggests that intense star formation activity is occurring at [FORMULA] 1, as also found for larger field galaxy samples at similar redshifts.

Key words: cosmology: observations – galaxies: evolution – galaxies: halos – quasars: absorption lines

* Based on observations made at the European Southern Observatory, La Silla, Chile (programme 1-012-43K)

Send offprint requests to: J. Bergeron (jbergero@eso.org)

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© European Southern Observatory (ESO) 1997

Online publication: March 26, 1998

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