Cosmological Evolution of the Duty Cycle of Quasars Yan-Mei Chen Collaborator: Jian-Min Wang, Fan Zhang Institute of High Energy Physics, CAS, China 21 Oct 2006

Outline Motivation The definition of duty cycle Black hole mass function Results

Background Continuity equation: Luminosity function Quasars’ duty cycle Ref: Marconi et al., 2004, MNRAS, 351, 169 Small & Blandford, 1992, MNRAS, 259, 725

Motivation During entire evolution, how many times and how many black holes are triggered ? What is the trigger mechanism and why do quasars switch off ? Constant Eddington ratio ? (Vestergaard, 2004, ApJ, 601, 676)

Duty cycle: episodic activity (Kharb et al., 2006) BH birth active dormant a single episodic phase today (1)For a single BH, ; (2)In statistic, duty cycle can be defined as the fraction of active BHs to their total number

Duty cycle: episodic activity Definition: where

Duty cycle The mass-averaged duty cycle: Soltan Argument (1982):

Sample Sample: SDSS DR3 (Richards et al. 2006) Total: 10, 979 Redshift: z<2.1 Estimation of BH mass (Mclure & Dunlop, 2004, MNRAS, 352, 1390)

Mass distribution Total: triple power law Mass function in each redshift z-bin

consistent with history of SFR density Main results: δ ∈ (10-3 , 1) strong evolution consistent with history of SFR density Open questions: how to explain the relation between δ and SFR density? feedback? duty cycle beyond z=2.1? how does duty cycle depend on BH mass? (Pablo G. Perez-Gonzalez et al., 2005, ApJ, 630, 82)

Thank You !