Clustering Analyses of 300,000 Photometrically Classified Quasars. II. The Excess on Very Small Scales

We study quasar clustering on small scales, modeling clustering amplitudesusing halo-driven dark matter descriptions. From 91 pairs on scales <35 kpc/h,we detect only a slight excess in quasar clustering over our best-fitlarge-scale model. Integrated across all redshifts, the implied quasar bias isb_Q = 4.21+/-0.98 (b_Q = 3.93+/-0.71) at ~18 kpc/h (~28 kpc/h). Our best-fit(real-space) power index is ~-2 (i.e., $\xi(r) \propto r^{-2}$), implyingsteeper halo profiles than currently found in simulations. Alternatively,quasar binaries with separation <35 kpc/h may trace merging galaxies, withtypical dynamical merger times t_d~(610+/-260)m^{-1/2} Myr/h, for quasars ofhost halo mass m x 10^{12} Msolar/h. We find UVX quasars at ~28 kpc/h cluster>5 times higher at z > 2, than at z < 2, at the $2.0\sigma$ level. However, asthe space density of quasars declines as z increases, an excess of quasarbinaries (over expectation) at z > 2 could be consistent with reduced mergerrates at z > 2 for the galaxies forming UVX quasars. Comparing our clusteringat ~28 kpc/h to a $\xi(r)=(r/4.8\Mpch)^{-1.53}$ power-law, we find an upperlimit on any excess of a factor of 4.3+/-1.3, which, noting some caveats,differs from large excesses recently measured for binary quasars, at$2.2\sigma$. We speculate that binary quasar surveys that are biased to z > 2may find inflated clustering excesses when compared to models fit at z < 2. Weprovide details of 111 photometrically classified quasar pairs with separations<0.1'. Spectroscopy of these pairs could significantly constrain quasardynamics in merging galaxies.Comment: 12pages, 3 figures, 2 tables; uses amulateapj; accepted to Ap