A 1.75 kpc/h Separation Dual AGN at z=0.36 in the COSMOS Field

We present strong evidence for dual active galactic nuclei (AGN) in the z=0.36 galaxy COSMOS J100043.15+020637.2. COSMOS Hubble Space Telescope (HST) imaging of the galaxy shows a tidal tail, indicating that the galaxy recently underwent a merger, as well as two bright point sources near the galaxy's center. Both the luminosities of these sources (derived from the HST image) and their emission line flux ratios (derived from Keck/DEIMOS slit spectroscopy) suggest that both are AGN and not star-forming regions or supernovae. Observations from zCOSMOS, Sloan Digital Sky Survey, XMM-Newton, Very Large Array, and Spitzer fortify the evidence for AGN activity. With HST imaging we measure a projected spatial offset between the two AGN of 1.75 +- 0.03 kpc/h, and with DEIMOS we measure a 150 +- 40 km/s line-of-sight velocity offset between the two AGN. Combined, these observations provide substantial evidence that COSMOS J100043.15+020637.2 is a dual AGN in a merger-remnant galaxy.