A DEEP SEARCH FOR FAINT GALAXIES ASSOCIATED WITH VERY LOW-REDSHIFT C IV ABSORBERS: A CASE WITH COLD-ACCRETION CHARACTERISTICS

摘要

Studies of QSO absorber–galaxy connections are often hindered by inadequate information on whether faint/dwarfgalaxies are located near the QSO sight lines. To investigate the contribution of faint galaxies to QSO absorberpopulations, we are conducting a deep galaxy redshift survey near low-z Civ absorbers. Here we report a blindlydetected C iv absorption system (zabs = 0.00348) in the spectrum of PG1148+549 that appears to be associatedeither with an edge-on dwarf galaxy with an obvious disk (UGC 6894, zgal = 0.00283) at an impact parameter ofρ = 190 kpc or with a very faint dwarf irregular galaxy at ρ = 23 kpc, which is closer to the sightline but has alarger redshift difference (zgal = 0.00107, i.e., δv = 724 km s−1). We consider various gas/galaxy associations,including infall and outflows. Based on current theoretical models, we conclude that the absorber is most likelytracing (1) the remnants of an outflow from a previous epoch, a so-called “ancient outflow”, or (2) intergalactic gasaccreting onto UGC 6894, “cold mode” accretion. The latter scenario is supported by Hi synthesis imaging datathat shows the rotation curve of the disk being codirectional with the velocity offset between UGC 6894 and theabsorber, which is located almost directly along the major axis of the edge-on disk.