SDSS J092712.64+294344.0: recoiling black hole or merging galaxies?

TL;DR

This study uses spectroscopic observations to investigate whether SDSS J092712+294344 is a recoiling black hole or a merging galaxy system, finding evidence inconsistent with a binary black hole but compatible with recoil or merging scenarios.

Contribution

The paper provides new spectroscopic data and analysis that challenge the binary black hole hypothesis for SDSS J092712+294344, supporting recoil or merging models.

Findings

Limited relative acceleration between emission regions (<32 km/s/yr)

Extended [OIII] emission region (~8 kpc)

Possible spatial offset of emission line centroid (~1 kpc)

Abstract

We report long-slit spectroscopic observations of SDSS J092712+294344 carried-out at the recently commissioned 2m telescope in IUCAA Girawali Observatory, India. This AGN-like source is known to feature three sets of emission lines at zem = 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 (SDSS), obtained 4 years prior to our observations. Comparing the redshifts of [OIII]4960,5008 we put a 3 sigma limit on the relative acceleration to be less than 32 km s^-1 yr^-1 between different emitting regions. Using the 2D spectra obtained at different position angles we show that the [OIII]5008 line from the zem = 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 [OIII]5008 line at zem = 0.7128 and the QSO trace when the slit is aligned at a position angle of 299 degrees. This corresponds to the zem = 0.7128 system being at an impact parameter of ~1 kpc with respect to the zem = 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.