Strong magnesium(II) absorbers and their relation to galaxies

The largest catalog of strong MgII absorbers to date derived from the Sloan Digital Sky Survey (SDSS) quasar spectra was employed to describe statistical properties of absorbers and their clustering along sight lines as a function of redshift and rest-equivalent width (REW). The association of SDSS galaxies with MgII systems was investigated by cross-correlating the spectroscopic MgII catalog with the imaging catalog of galaxies surrounding quasar sight lines. The quasar-galaxy cross-correlation was estimated for various subsets in redshift, REW, and magnitude intervals as a function of impact parameter from quasar sight lines. The distribution of luminosities of MgII-absorbing galaxies was described using a background subtraction method. Photometric properties of absorbing galaxies, such as colors and integrated fluxes in various bands, were analyzed as a function of REW. An analytical model for the absorbers was developed and constrained by the statistical properties of the MgII catalog and observational features of high-redshift galaxies from the Hubble Ultra Deep Field (HUDF), which were also employed to determine the evolution of absorption cross-section.; Clustering was detected for absorbers separated by less than ∼500 km s-1, with indications of a stronger signal at larger REW and growing clustering at lower redshift. An anti-correlation feature was found at absorption pair separations of about 103 km s-1. The shallow nature of SDSS galaxy imaging limited the analysis of MgII-galaxy associations to lower redshift absorbers and only the bright end of the luminosity distribution of absorbing galaxies was recovered. The quasar-galaxy cross-correlation showed evidence for a MgII galaxy association and was stronger and steeper at small impact parameters for larger REW absorption lines. Stronger absorbers were found to be associated with bluer and less luminous galaxies, while weaker systems were associated with redder and more luminous galaxies. The cross-section of absorbers inferred from the distribution of HUDF galaxies confirmed smaller impact parameters and increasing evolutionary effects for stronger absorbers. Modeling absorbers indirectly via HUDF galaxies led to a versatile tool able to guide measurements toward a deeper understanding of the origins of MgII absorption.