quasar luminosity functions at high redshifts gordon richards drexel university with thanks to...
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Quasar Luminosity Functions at High Redshifts
Gordon Richards
Drexel University
With thanks to Michael Strauss, Xiaohui Fan, Don Schneider, and Linhua Jiang
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Quasar Luminosity Function
Croom et al. 2004
Space density of quasars as a function of redshift and luminosity
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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
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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
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Quasar Luminosity Function
Croom et al. 2004
Space density of quasars as a function of redshift and luminosity
Typically fit by double power-law
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Parameterization of the QLF
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Density Evolution
Number of quasars is changing as a function of time.
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Luminosity Evolution
Space density of quasars is constant.
Brightness of individual (long-lived) quasars is changing.
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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.
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Cosmic Downsizing
Hasinger et al. 2005
X-ray surveys probe muchlarger dynamic range.
SDSS+2SLAQCroom, Richards et al. 2009 See also Bongiorno et al. 2007 (VVDS)
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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.
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Luminosity vs. Redshift
PLE vs. Luminosity and vs. Redshift
0.5
1.5
2.5
3.54.5
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Luminosity Evolution
• Pure density or pure luminosity evolution don’t lead to cosmic downsizing.• The slopes must evolve with redshift.
Cosmic Downsizing
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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.
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Bolometric QLF
Hopkins, Richards, & Hernquist 2007
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Jiang et al. 2009
At z~6, slope is flatter than for z<2.But not as flat at the z~4 SDSS measurement.
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Willott et al. 2010
CFHTLS probes faint enough to see evidence for a break at z~6.
Bright-ned slope flatter than high-z.
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Photo-ionization Rate
Volume emissivity
Photo-ionization rate (per hydrogen atom)
Siana et al. 2008
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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.”
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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.
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QSO QLF != Galaxy QLF
Benson et al. 2003
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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
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Constraints from Lensing (or Lack Thereof)
At z~5
Richards et al. 2006