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Astron. Astrophys. 328, 499-509

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Evolution of quasar absorption-selected galaxies*

P. Guillemin1 and J. Bergeron2,1

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

Received 19 August 1996 / Accepted 27 May 1997


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 0.7<z<1.2 with $\left<z\right\gt$=0.9, and is combined with a lower redshift (z<0.7) 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 $z\simeq1$, 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]$\lambda 3727$ emission line and the rest-frame luminosity M$M_{\rm{AB}}$(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 ($z\mathrel{\mathchoice {\vcenter{\offinterlineskip\halign{\hfil
$\displaystyle ... ) samples, we have built template spectra by combining individual galaxy spectra. The lack of detection of the [N II] emission line in the low-redshift template, [N II]$\lambda$6568/H$\alpha <$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]=-0.6,-0.1. The spectral energy distribution (SED) of these templates at $\lambda_{\rm{r}} \gt$3646Åcan be fitted by present-day Sbc or Sc galaxies, but the UV excess at $\lambda_{\rm{r}} <$3500Å follows the SED of Scd and Im present-day galaxies at $\left<z\right\gt$=0.4 and 0.9 respectively. This blueing of the SED with redshift is associated with an increase of $w_{\rm{r}}$([O II]$\lambda 3727$) 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 $\mathrel{\mathchoice {\vcenter{\offinterlineskip\halign{\hfil
$\displaystyle ... ). 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 $\left<z\right\gt$=0.4 and 0.9 Mg II absorbing galaxies. Results for the blue subtemplates using Sc galaxy models, especially that at $\left<z\right\gt$=0.9, suggests that intense star formation activity is occurring at $z\simeq$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)

© European Southern Observatory (ESO) 1997

Online publication: November 24, 1997
Last change: March 26, 1998