Quasar Luminosity Functions at High Redshifts
Gordon RichardsDrexel University
With thanks to Michael Strauss, Xiaohui Fan, Don Schneider, and Linhua Jiang
Quasar Luminosity Function
Croom et al. 2004
Space density of quasars as a function of redshift and luminosity
QLF: Luminosity vs. Redshift
Usually we split into L or z instead of making a 3-D plot, but the information is the same.
0.5
1.5
2.5
3.54.5
Hopkins et al. 2005
Hopkins et al. 2006
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.
old model
Lidz et al. 2006
new model
Quasar Luminosity Function
Croom et al. 2004
Space density of quasars as a function of redshift and luminosity
Typically fit by double power-law
Parameterization of the QLF
Density Evolution
Number of quasars is changing as a function of time.
Luminosity EvolutionSpace density of quasars is constant.
Brightness of individual (long-lived) quasars is changing.
Cosmic Downsizing
Ueda et al. 2003
Hasinger et al. 2005
X-ray surveys probe much deeper than optical and reveal that the peak depends on the luminosity.
Cosmic Downsizing
Hasinger et al. 2005
X-ray surveys probe muchlarger dynamic range. SDSS+2SLAQ
Croom, Richards et al. 2009 See also Bongiorno et al. 2007 (VVDS)
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.
Luminosity vs. Redshift
PLE vs. Luminosity and vs. Redshift
0.5
1.5
2.5
3.54.5
Luminosity Evolution
• Pure density or pure luminosity evolution don’t lead to cosmic downsizing.• The slopes must evolve with redshift.
Cosmic Downsizing
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.
Bolometric QLF
Hopkins, Richards, & Hernquist 2007
Jiang et al. 2009
At z~6, slope is flatter than for z<2.But not as flat at the z~4 SDSS measurement.
Willott et al. 2010
CFHTLS probes faint enough to see evidence for a break at z~6.
Bright-ned slope flatter than high-z.
Photo-ionization Rate
Volume emissivity
Photo-ionization rate (per hydrogen atom)
Siana et al. 2008
Photoionization Rate at z~6
Willot et al. 2010
“… the quasar population … is insufficient to get even close to the required photon emission rate density. … the photon rate density is between20 and 100 times lower than the required rate.”
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.
QSO QLF != Galaxy QLF
Benson et al. 2003
Clustering’s Luminosity Dependence
• 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
old model
Lidz et al. 2006
new model
Constraints from Lensing (or Lack Thereof)
At z~5
Richards et al. 2006
