SIMBAD references

We present a sample of 221 new quasar pairs with proper transverse separations R_prop<1 h^–1 Mpc over the redshift range 0.5<z<3.0, discovered from an extensive follow-up campaign to find companions around the Sloan Digital Sky Survey and 2dF QSO Redshift Survey quasars. This sample includes 26 new binary quasars with separations R_prop<50 h^–1 kpc (θ<10''), more than doubling the number of such systems known. We define a statistical sample of binaries selected with homogeneous criteria and compute its selection function, taking into account sources of incompleteness. The first measurement of the quasar correlation function on scales 10 h^–1 kpc<R_prop<400 h^–1 kpc is presented. For R_prop≲40 h^–1 kpc, we detect an order of magnitude excess clustering over the expectation from the large-scale (R_prop≳3 h^–1 Mpc) quasar correlation function, extrapolated down as a power law (γ=1.53) to the separations probed by our binaries. The excess grows to ∼30 at R_prop∼10 h^–1 kpc and provides compelling evidence that the quasar autocorrelation function gets progressively steeper on submegaparsec scales. This small-scale excess can likely be attributed to dissipative interaction events that trigger quasar activity in rich environments. Recent small-scale measurements of galaxy clustering and quasar-galaxy clustering are reviewed and discussed in relation to our measurement of small-scale quasar clustering.