A Unique Merging Pair among Luminous Binary Quasars: SDSS J1254+0846

SDSS J1254+0846 is the first luminous, spatially resolved binary quasar that clearly inhabits an ongoing galaxy merger. These two luminous (z=0.44) radio quiet quasars, with a radial velocity difference of just 215 km/s, are separated on the sky by 21 kpc in a disturbed host galaxy merger showing broad, symmetrical tidal arm features spanning some 75 kpc at the quasars' redshift. Our semi-analytic modeling suggests that the system consists of two massive disk galaxies prograde to their mutual orbit, caught during the first passage of an active merger. This demonstrates rapid black hole growth during the early stages of a merger between galaxies with pre-existing bulges. Neither of the two luminous nuclei show significant instrinsic absorption by gas or dust in our optical or X-ray observations, illustrating that not all merging quasars will be in an obscured, ultraluminous phase. We find that the Eddington ratio for the fainter component B is rather normal, while for the A component it is quite high compared to quasars of similar luminosity and redshift, possibly evidence for strong merger-triggered accretion. More such mergers should be identifiable at higher redshifts using binary quasars as tracers. We further present Chandra imaging results for a sample of 14 quasars in spatially-resolved pairs. The pairs were all targeted as part of a complete sample of binary quasar candidates with small transverse separations drawn from SDSS DR6 photometry.