1. 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

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

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

4. 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)

5. 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

6. Duty cycle: episodic activity
Definition:
where

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

8. 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)

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

10. 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)

11. Thank You !