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SDSS J1254+0846: Quasar Pair Captured in Galaxy Collision

sdss_w1.jpg
Credit: X-ray (NASA/CXC/SAO/P. Green et al.), Optical (Carnegie Obs./Magellan/W.Baade Telescope/J.S.Mulchaey et al.)

This composite image shows the effects of two galaxies caught in the act of merging. A Chandra X-ray Observatory image shows a pair of quasars in blue, located about 4.6 billion light years away, but separated on the sky by only about 70 thousand light years. These bright sources, collectively called SDSS J1254+0846, are powered by material falling onto supermassive black holes. An optical image from the Baade-Magellan telescope in Chile, in yellow, shows tidal tails - gravitational-stripped streamers of stars and gas -- fanning out from the two colliding galaxies.
This represents the first time a luminous pair of quasars has been clearly seen in an ongoing galaxy merger.

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Position (2000): RA 12h 54m 54.90s | Dec +08 46' 52.30"

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Magellan_r1arcmin_BlackSky02Feb2010.jpg
Credit: Carnegie Institution

This optical image of SDSS J1254+0846 obtained May 22, 2009 on the IMACS camera at the Magellan/Baade telescope at Las Campanas Observatory in Chile shows the two bright quasar nuclei as well as the tidal arms of the host galaxy merger. Scale bar is 10 arcseconds.

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Caught in the act: a merging binary QSO

It has been assumed for some time that binary supermassive black holes (SMBH) should be common in the universe, given that galaxies regularly interact and merge and that most, if not all, galaxies contain a SMBH. Such a SMBH will only be detected as a quasar when it is accreting matter. And galaxy merging is a leading proposal to trigger such accretion. Now the first luminous, spatially resolved binary quasar that clearly inhabits an interacting/merging galaxy pair has been reported.
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Title: SDSS J1254+0846: A Binary Quasar Caught in the Act of Merging
Authors: Paul J. Green (1), Adam D. Myers (2), Wayne A. Barkhouse (3), John S. Mulchaey (4), Vardha N. Bennert (5), Thomas J. Cox (1,3), Thomas L. Aldcroft (1) ((1) Harvard-Smithsonian Centre for Astrophysics, (2) University of Illinois at Urbana-Champaign (3) University of North Dakota, Grand Forks (4) The Observatories of the Carnegie Institution for Science, (5) University of California, Santa Barbara)
(Version v2)

We present the first luminous, spatially resolved binary quasar that clearly inhabits an ongoing galaxy merger. SDSS J125455.09+084653.9 and SDSS J125454.87+084652.1 (SDSS J1254+0846 hereafter) are two luminous z=0.44 radio quiet quasars, with a radial velocity difference of just 215 km/s, separated on the sky by 21 kpc in a disturbed host galaxy merger showing obvious tidal tails. The pair was targeted as part of a complete sample of binary quasar candidates with small transverse separations drawn from SDSS DR6 photometry. We present follow-up optical imaging which shows broad, symmetrical tidal arm features spanning some 75 kpc at the quasars' redshift. Numerical modelling 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 L/LEdd is quite (>3sigma) 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.

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