Quasar Luminosity Functions at High Redshifts

1. Quasar Luminosity Functions at High Redshifts Gordon Richards Drexel University With thanks to Michael Strauss, Xiaohui Fan, Don Schneider, and Linhua Jiang

2. Quasar Luminosity Function Space density of quasars as a function of redshift and luminosity Croom et al. 2004

3. QLF: Luminosity vs. Redshift 2.5 1.5 4.5 3.5 0.5 Usually we split into L or z instead of making a 3-D plot, but the information is the same.

4. Hopkins et al. 2005 Most QLF models assume they are either “on” or “off” and that there is a mass/luminosity hierarchy. Hopkins et al.: quasar phase is episodic with a much smaller range of mass than previously thought. QLF is the convolution of the formation rate and the lifetime. Lidz et al. 2006 old model new model Hopkins et al. 2006

5. Quasar Luminosity Function Space density of quasars as a function of redshift and luminosity Typically fit by double power-law Croom et al. 2004

6. Parameterization of the QLF

7. Density Evolution Number of quasars is changing as a function of time.

8. Luminosity Evolution Space density of quasars is constant. Brightness of individual (long-lived) quasars is changing.

9. Cosmic Downsizing Hasinger et al. 2005 X-ray surveys probe much deeper than optical and reveal that the peak depends on the luminosity. Ueda et al. 2003

10. Cosmic Downsizing Hasinger et al. 2005 X-ray surveys probe much larger dynamic range. SDSS+2SLAQ Croom, Richards et al. 2009 See also Bongiorno et al. 2007 (VVDS)

11. Luminosity Dependent Density Evolution To get cosmic downsizing, the number of quasar must change as a function of time, as a function of luminosity. i.e., the slopes must evolve.

12. Luminosity vs. Redshift 2.5 1.5 4.5 3.5 0.5 PLE vs. Luminosity and vs. Redshift

13. Luminosity Evolution Cosmic Downsizing • Pure density or pure luminosity evolution don’t lead to cosmic downsizing. • The slopes must evolve with redshift.

14. Richards et al. 2006 Bright end slope flattens with redshift at high-z. Similarly in Fan et al. 2001 Fontanot et al. 2007 argue (with 11 objects) that this is a selection effect.

15. Bolometric QLF Hopkins, Richards, & Hernquist 2007

16. Jiang et al. 2009 At z~6, slope is flatter than for z<2. But not as flat at the z~4 SDSS measurement.

17. Willott et al. 2010 Bright-ned slope flatter than high-z. CFHTLS probes faint enough to see evidence for a break at z~6.

18. Photo-ionization Rate Photo-ionization rate (per hydrogen atom) Volume emissivity Siana et al. 2008

19. Photoionization Rate at z~6 “… the quasar population … is insufficient to get even close to the required photon emission rate density. … the photon rate density is between 20 and 100 times lower than the required rate.” Willot et al. 2010

20. Conclusions • We need better measurements of both the bright and faint end slopes of the z>4 QLF • Current measurements of the QLF allow one to get whatever answer you want (or don’t want) for the number of faint high-z quasars and the resulting re-ionization rate.

21. QSO QLF != Galaxy QLF Benson et al. 2003

22. Clustering’s Luminosity Dependence Lidz et al. 2006 old model new model • Quasars accreting over a wide range of luminosity are driven by a narrow range of black hole masses • M- relation means a wide range of quasar luminosities will then occupy a narrow range of MDMH

23. Constraints from Lensing (or Lack Thereof) At z~5 Richards et al. 2006