Test of evolution models of QSOs

Abstract

Under the assumption that QSOs spectral states are strongly related to luminosities, we directly apply the observed spectral states of the Galactic Black Hole Candidates (GBHCs) to the spectral states which an individual QSO could undergo over cosmological timescale, which is supported by the observational analogies of their emission mechanisms, and derive the QSO luminosity functions (LFs) in different energy bands (optical/UV, soft X-ray, and hard X-ray). We test one of the cosmological evolution scenarios of QSOs. in which a single population composed of long-live (> 10 9 y) QSOs forming at high z becomes gradually dimmer over the cosmological timescale while the number of QSOs is conserved throughout the evolution (pure luminosity evolution model). We show that the various luminosity evolution trends in different energy bands are largely consistent with the observation and especially, characteristic and potentially observable evolution signatures in the hard X-ray energy bands could provide a supporting evidence for this scenario of a single long-lived population of QSOs with spectral evolution.