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Cross-Correlation of SDSS DR7 Quasars and DR10 BOSS Galaxies: The Weak Luminosity Dependence of Quasar Clustering at z~0.5

We present the measurement of the two-point cross-correlation function (CCF) of 8,198 Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) quasars and 349,608 DR10 CMASS galaxies from the Baryonic Oscillation Spectroscopic Survey (BOSS) at redshift <z>~0.5 (0.3<z<0.9). The cross-correlation function can be reasonably well fit by a power-law model xi_QG(r)=(r/r_0)^(-gamma) on projected scales of r_p=2-25 Mpc/h with r_0=6.61+-0.25 Mpc/h and gamma=1.69+-0.07. We estimate a quasar linear bias of b_Q=1.38+-0.10 at <z>=0.53 from the CCF measurements. This linear bias corresponds to a characteristic host halo mass of ~4x10^12 M_sun/h, compared to ~10^13 M_sun/h characteristic host halo mass for CMASS galaxies. We divide the quasar sample in luminosity and constrain the luminosity dependence of quasar bias to be db_Q/dlogL=0.20+-0.34 or 0.11+-0.32 (depending on different luminosity divisions) for quasar luminosities -23.5>M_i(z=2)>-25.5, implying a weak luminosity dependence of quasar clustering for the bright end of the quasar population at <z>~0.5. We compare our measurements with theoretical predictions, Halo Occupation Distribution (HOD) models and mock catalogs. These comparisons suggest quasars reside in a broad range of host halos, and the host halo mass distributions significantly overlap with each other for quasars at different luminosities, implying a poor correlation between halo mass and instantaneous quasar luminosity. We also find that the quasar HOD parameterization is largely degenerate such that different HODs can reproduce the CCF equally well, but with different outcomes such as the satellite fraction and host halo mass distribution. These results highlight the limitations and ambiguities in modeling the distribution of quasars with the standard HOD approach and the need for additional information in populating quasars in dark matter halos with HOD. [Abridged]