your ID: 0311 
First Name: YanMei 
Last Name: Chen 
Affiliation: Institute of High Energy Physics, CAS, China

Title: Cosmological Evolution of the Duty Cycle of Quasars 
Authors: JianMin Wang, YanMei Chen, FanZhang 
Topic: 9 
Session: oral 

Abstract: 
Quasars are powered by accretion onto supermassive black holes, 
but the problem of the duty cycle related to the episodic activity of
 the black holes remains open as one of the major questions of 
cosmological evolution of quasars. We obtain quasar duty cycles 
based on analyses of a large sample composed of 10,979 quasars 
with redshifts $z\\le2.1$ from the Sloan Digital Sky Survey (SDSS) 
Data Release Three. We estimate masses of quasar black holes and 
obtain their mass function of the present sample.  We then get the 
duty cycle $\\bar{\\delta}(z)=10^{-3}\\sim 1$ based on the So\\l tan\'s 
argument, implying that black holes are undergoing multiple episodic 
activity. We find that the duty cycle has a strong evolution. By comparison, 
we show that evolution of the duty cycle follows the history of cosmic 
star formation rate (SFR) density in the Universe, providing intriguing 
evidence for a natural connection between star formation and triggering 
of black hole activity. Feedback on star formation from black hole activity 
is briefly discussed.