SDSSJ092712.64+294344.0: recoiling blackhole or merging galaxies?

Abstract

We report long-slit spectroscopic observations of SDSSJ092712+294344 carried out at the recently commissioned 2-m telescope in IUCAA Girawali Observatory, India. This active galactic nuclei like source is known to feature three sets of emission lines at z_em= 0.6972, 0.7020 and 0.7128. Different scenarios such as a recoiling black hole after asymmetric emission of gravitational waves, binary black holes and possible merging systems are proposed for this object. We test these scenarios by comparing our spectra with that from the Sloan Digital Sky Survey, obtained 4 years prior to our observations. Comparing the redshifts of [O III] λλ4960,5008, we put a 3σ limit on the relative acceleration to be less than 32 km s^-1 yr^-1 between different emitting regions. Using the two-dimensional spectra obtained at different position angles (PAs), we show that the [O III] λ5008 line from the z_em= 0.7128 component is extended beyond the spectral point spread function. We infer the linear extent of this line emitting region is ∼8 kpc. We also find a tentative evidence for an offset between the centroid of the [O III] λ5008 line at z_em= 0.7128 and the quasi-stellar object trace when the slit is aligned at a PA of 299°. This corresponds to the z_em= 0.7128 system being at an impact parameter of ∼1 kpc with respect to the z_em= 0.6972 in the north-west direction. Based on our observations, we conclude that the binary black hole model is most unlikely. The spatial extent and the sizes are consistent with both black hole recoil and merging scenarios.