Demographics of SDSS Quasars in Two-Dimension Yue Shen Carnegie Observatories In collaboration with Brandon Kelly (UCSB)

Motivation The abundance (and clustering) of quasars are key to understand the evolution of quasars/SMBHs in the hierarchical structure formation paradigm Abundance measurements form a basis for any cosmological quasar models Likely tied to formation and evolution of galaxies Key science goal in many current and upcoming extragalactic survey programs

Quasar Luminosity Function Evolves strongly with redshift The space density of bright quasars peaks around z~2-3 Richards et al. (2006, SDSS DR3)

Z= For bright quasars, the abundance follows a “pure luminosity evolution” (PLE)  a fading, long-lived quasar population? PLE Such a simple picture doesn’t fit other observations. SDSS DR7 LF (Shen & Kelly 2012)

Quasar clustering measurements suggest low-z quasars are not simply the descendants of high-z quasars Dashed lines: predicted evolution of the linear bias for a passive population z~2 quasars should end up in cluster-sized environment at z~0.5 YS, McBride, White, Zheng, et al. (2013)

Quasars evolve in the mass-luminosity plane A better representation of the evolution of the quasar population Contains richer information about the growth of SMBHs Virial masses

Estimating quasar BH masses The broad-line region (BLR) is assumed to be virialized BLR size (reverberation mapping) Virial velocity Reverberation mapping is time consuming, and we only have BLR size measured this way for ~40 AGNs

Reverberation mapping  R~Lb (Kaspi et al. 2000) b~0.5, Consistent with naive predictions of photoionization models Bentz et al. (2009)

Single-epoch virial BH mass estimators Continuum luminosity Broad line width Vestergaard & Peterson(2006), McLure & Dunlop (2004), Greene et al. (2005), and many more … Currently the only practical method to estimate BH mass for large spectroscopic quasar samples Many physical and practical concerns that need to be addressed (Shen 2013): we are extrapolating from ~40 local AGNs with reverberation mapping data to high-z, high-luminosity quasars Large uncertainties for individual BH mass estimates: ~ a factor of 3 (~0.5 dex)

Quasar abundance in the mass-luminosity plane The sample used: ~58,000 uniformly selected DR7 SDSS quasars, with good spectra to estimate BH mass Two major problems: Flux limit of the sample Scatter in BH mass due to errors in mass estimates Virial masses

Forward modeling in the mass-luminosity plane (Shen & Kelly 2012, Kelly & Shen 2013) Flux limit and mass errors are more easily accounted for More information is preserved True BH masses

LF BHMF Caveats: SDSS only probes the tip of the quasar population, poorly constraining the faint-end of the LF and the low-mass end of the BHMF – need deeper data Systematic uncertainties of quasar BH mass estimates have dramatic effects on the BHMF estimates – need to improve the BH weighing method

Downsizing in terms of quasar luminosity and BH mass

Properly accounting for the selection effect of flux-limited samples and errors in the virial BH mass estimates Eddington limit Interpret the “observed distributions” with caution Flux limit Red: true mass Black: virial mass estimates

Summary Instead of measuring LF and BHMF separately, measure 2D density in the M-L plane (if you have a spectroscopic sample); this gives you more information on the evolution of the quasar population Forward modeling in the M-L plane makes it easier to account for the sample flux-limit and errors in mass estimates The “observed” distribution in the M-L plane is biased; don’t interpret it directly! There is urgent need to improve quasar BH mass weighing methods (~0.5 dex error is inconvenient)