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A deep imaging survey of fields around quasars with z<1.2 Mg II absorption systems

The high success rate of identification of galaxies causing Mg II absorption in quasar spectra suggests that Mg II absorbers are associated with bright field galaxies with large gaseous halos of radius R∼3 to 4R H . An alternative origin for the absorption could be in clustered groups of dwarf galaxies. To investigate further the nature of the galaxies responsible for quasar absorption systems, we have conducted a deep imaging survey in the r band at the CFH telescope of 12 fields around quasars with 17 Mg II absorption systems at redshift z a <1.2 with an average detection limit m r (3σ sky )=25.0. For the 14 confirmed MgII absorption systems, there is always an absorber candidate in the absolute magnitude range −23.0≤M r (z a )≤−19.5 at a linear separation from the quasar sight-line l<4R H except in one case for which l∼4.4 R H