Clustering of Low-Redshift (z <= 2.2) Quasars from the Sloan Digital Sky
  Survey
  We present measurements of the quasar two-point correlation function,
\xi_{Q}, over the redshift range z=0.3-2.2 based upon data from the SDSS. Using
a homogeneous sample of 30,239 quasars with spectroscopic redshifts from the
DR5 Quasar Catalogue, our study represents the largest sample used for this
type of investigation to date. With this redshift range and an areal coverage
of approx 4,000 deg^2, we sample over 25 h^-3 Gpc^3 (comoving) assuming the
current LCDM cosmology. Over this redshift range, we find that the
redshift-space correlation function, xi(s), is adequately fit by a single
power-law, with s_{0}=5.95+/-0.45 h^-1 Mpc and \gamma_{s}=1.16+0.11-0.16 when
fit over s=1-25 h^-1 Mpc. Using the projected correlation function we calculate
the real-space correlation length, r_{0}=5.45+0.35-0.45 h^-1 Mpc and
\gamma=1.90+0.04-0.03, over scales of rp=1-130 h^-1 Mpc. Dividing the sample
into redshift slices, we find very little, if any, evidence for the evolution
of quasar clustering, with the redshift-space correlation length staying
roughly constant at s_{0} ~ 6-7 h^-1 Mpc at z<2.2 (and only increasing at
redshifts greater than this). Comparing our clustering measurements to those
reported for X-ray selected AGN at z=0.5-1, we find reasonable agreement in
some cases but significantly lower correlation lengths in others. We find that
the linear bias evolves from b~1.4 at z=0.5 to b~3 at z=2.2, with
b(z=1.27)=2.06+/-0.03 for the full sample. We compare our data to analytical
models and infer that quasars inhabit dark matter haloes of constant mass M ~2
x 10^12 h^-1 M_Sol from redshifts z~2.5 (the peak of quasar activity) to z~0.
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