A search for galaxies producing CIV absorption in QSO spectra

Abstract

This thesis describes an infrared search for the intervening galaxies responsible for some of the heavy-element absorption lines observed in QSO spectra. Deep K-band images have been obtained of 11 QSOs whose spectra are known to contain multiple CIV absorption systems in the redshift range 1.2 ˂ z ˂ 2.0. After background subtraction, a clear excess of sources is detected within a small angular separation (≈ 6."0) of the QSOs. We discuss the possible origins of this excess, in particular the hypotheses that the excess arises from QSO-galaxy associations or from MgII systems at lower redshifts, but consider them unlikely in the light of previous studies. We thus conclude that the excess objects are most likely to be associated with the CIV absorption systems. Prom a final sample of 19 candidate absorbers with a mean redshift 1 - 1.6, we find that the absorbing candidate population consists of bright L* galaxies whose luminosities are similar to their present-day counterparts. Their linear impact parameters (30-40h(^-1) kpc) are found to be similar to those of spectroscopically-confirmed Mgll absorbers at lower redshifts, ruling out significant evolution in galactic halo sizes from z ~ 1.6 to z ~ 0.5. Optical R and /-band photometry of four fields is also presented, allowing us to determine optical-infrared colours for a subsample of our candidates; these are found to be typical of late-type, star-forming galaxies. We thus find that our candidate absorbers share several properties with the galaxies known to give rise to lower redshift MgII absorption lines.