WFPC2 Imaging of Quasar Environments: A Comparison of LBQS and HST Archive Quasars

We present Hubble Space Telescope (HST ) Wide Field Planetary Camera 2 (WFPC2) data on the large-scale environments of 16 0.39 < z < 0.51 quasars from the Large Bright Quasar Survey (LBQS). The LBQS quasars are representative of the radio-quiet population, and this is the first look at their large-scale environments. We compare the LBQS environments with the environments of 27 0.15 < z < 0.55 quasars selected from the HST Archive. The majority of the Archive quasars are from the PG and PKS surveys, and these quasars are more luminous on average than the LBQS. By comparing the LBQS and Archive environments, we investigate whether previous quasar environment studies have been biased due to studying unusually radio or optically luminous quasars. We compare observed galaxy number counts with expected counts predicted from the CNOC2 field-galaxy luminosity function in order to look for statistical excesses of galaxies around the quasars. We detect a significant excess around the Archive quasars but find no such excess around the LBQS quasars. We calculate the amplitude of the spatial correlation function and find that the LBQS environments are consistent with that of the typical galaxy while the Archive environments are slightly Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc.