Key points are not available for this paper at this time.
From direct imaging data, quantitative measures of the richness of the environment of quasars are derived using self-consistent galaxy luminosity function and galaxy count models. These models are obtained using the following procedure. By assuming that the excess galaxies found in the quasar fields are situated at the cosmological distance of the quasar redshifts and correcting for the background galaxy counts using control field counts, crude luminosity functions (LFs) of galaxies at three redshift bins centered at z = 0.24, 0.42, and 0.61 are determined for different values of q0. The absolute magnitudes of the excess galaxies are found to be consistent with that of galaxies at the cosmological redshift distances of the quasars. Using these measured LFs to estimate the evolution of galaxies and the current knowledge of the LF of local galaxies, self-consistent galaxy-count models are derived by comparing the computed galaxy counts with the control field galaxy counts. The best fitting models have q0 = 0-0.5, depending on the adopted faint-end slope of the LF of local galaxies. The evolution of galaxies at z≍ 0.6 is equivalent to a brightening of 0.9 ± 0.5 mag for the best fitting models. However, because of the large statistical uncertainty in our background galaxy counts from a small total area, we can only constrain q0 formally to be ≤ 1.5 at the 2 σ level. With these self-consistent world models, the quasar-galaxy covariance function is derived for samples of quasars having redshifts ranging from 0.05 to 0.65. The power-law slope of the covariance function is found to be entirely consistent with that of the galaxy-galaxy covariance function. Between z ≍ 0.4 and 0.6, there is an increase by a factor of ∼3 in the average quasar-galaxy covariance amplitude for radio-loud quasars. Some radio-loud quasars at z ≍ 0.6 are found in environments as rich as those of Abell class 1 clusters. This indicates that there has been significant evolution in the environments within some rich clusters over a time period of the order of one billion years, allowing them to support quasar activity at the earlier epoch. The apparent difference in the evolution time scale for quasars in different environments suggests that physical environmental conditions play a significant role in the evolution of quasars, implying that the evolution of the luminosity function of quasars cannot be entirely described by simple luminosity evolution models.
Yee et al. (Sat,) studied this question.