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

Quasar Luminosity Function Croom et al 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

Hopkins et al Hopkins et al 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 new model

Quasar Luminosity Function Croom et al 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 Evolution Space density of quasars is constant. Brightness of individual (long-lived) quasars is changing.

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

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

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

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

Bolometric QLF Hopkins, Richards, & Hernquist 2007

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

Willott et al 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 “… 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.”

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. 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 M DMH old model Lidz et al new model

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

Quasar Luminosity Function SDSS is relatively shallow. It probes only the tip of the iceberg. Need fainter surveys to get full picture. e.g., Richards et al. 2006

Quasar Luminosity Function SDSS is relatively shallow. It probes only the tip of the iceberg. Need fainter surveys to get full picture. e.g., Richards et al. 2006

No L Dependence for Quasars Zehavi et al galaxies Shen et al quasars

What We (Used To) Expect 1.Galaxies (and their DM halos) grow through hierarchical mergers 2.Quasars inhabit rarer high-density peaks 3.If quasars long lived, their BHs grow with cosmic time 4.M BH -σ relation implies that the most luminous quasars are in the most massive halos. 5.More luminous quasars should be more strongly clustered (b/c sample higher mass peaks). 6.QLF from wide range of BH masses (DMH masses) and narrow range of accretion rates.

What We Get 1.Galaxies (and their DM halos) grow through hierarchical mergers 2.Something causes the growth of galaxies and their BHs to terminate even as DM halos continue to grow 3.Quasars always turn on in potential wells of a certain size (at earlier times these correspond to relatively higher density peaks). 4.Quasars turn off on timescales shorter than hierarchical merger times, are always seen in similar mass halos (on average). 5.M BH -σ relation then implies that quasars trace similar mass black holes (on average) 6.Thus little luminosity dependence to quasar clustering (L depends on accretion rate more than mass). 7.Need a wide range of accretion rates for a narrow range of MBH to be consistent with QLF.

Luminosity-Dependent Density Evolution Ueda et al. (2003) AKA: Comsic Downsizing

Quasar Luminosity Function Quasars peaked around a redshift of 2.5 e.g., Richards et al. 2006

Hopkins et al Most QLF models assume they are either “on” or “off” and that there is a mass/luminosity heirarchy. Hopkins et al.: quasar phase is episodic and “all quasars are created equal” (with regard to mass/luminosity).

The SDSS QLF SDSS, though relatively shallow, allows us to determine the QLF from z=0 to z=5 with a single dataset. Richards et al. (2006) QLF slope flattens at high-z. Not PDE, PLE

Understanding the High-z QLF The change of the bright slope in the QLF at high redshift means the distribution of intrinsic luminosities is broader at high redshift. Hopkins et al Richards et al. 2006

QLF Comparison

Quasar Evolution The intrinsic properties of quasars have changed relatively little over cosmic time.The intrinsic properties of quasars have changed relatively little over cosmic time. Fan et al. 2004, 2008 Vignali et al. 2005; Shemmer et al NV OI SiIV Ly a Ly a forest z~6 composite Low-z composite

The Rise of Quasars at z~6 z~6 quasars constrain formation models due to their large masses and short ages. e.g., Richards et al. 2006

High-z Quasars Lensed? One way to get around such large masses at early times is if high-z quasars are gravitationally lensed (magnified). However, HST imaging suggests that they are not. Richards et al. 2004a

Quasar Luminosity Function As with star formation rate, quasars peaked at redshift 2-3. Richards et al The rise and fall is even more dramatic in time than redshift.

The Rise of Quasars at z~6 Mere existence z~6 quasars constrains formation models Eddington argument: If the luminosity of a quasar is high enough, then radiation pressure from electron scattering will prevent further gravitational infall. L E = 1.38x10 38 M/M sun erg/s M E = 8x10 7 L 46 M sun Sets an upper limit to the luminosity for a given mass, or equivalently a minimum mass for a given luminosity.

Making SMBHs at z~6 The luminosities of the z~6 quasars imply BH masses in excess of 10 9 M Sun. But z~6 is <1Gyr after the Big Bang. Assembling that much mass in so little time is difficult (but not impossible). Tanaka & Haiman 2009