Probing the nature of the massive black hole binary candidate SDSS J1536+0441

TL;DR

This study uses high-resolution imaging to investigate the environment of the candidate massive black hole binary SDSS J1536+0441, revealing a nearby galaxy and a galaxy cluster, which may influence the binary's properties.

Contribution

First detailed imaging analysis of SDSS J1536+0441 revealing a companion galaxy and its environment, providing insights into its potential binary nature.

Findings

Detection of a companion galaxy ~5 kpc from the quasar

Identification of an over-density of galaxies at similar redshift

Host galaxy is marginally resolved with a faint nucleus

Abstract

We present an imaging study of the black hole binary candidate SDSS J1536+0441 (z=0.3893), based on deep, high resolution VzK images collected at the ESO/VLT. The images clearly show an asymmetric elongation, indicating the presence of a companion source at ~1" (~5 kpc projected distance) East from the quasar. The host galaxy of the quasar is marginally resolved. We find that the companion source is a luminous galaxy, the light profile of which suggests the presence of an unresolved, faint nucleus (either an obscured AGN or a compact stellar bulge). The study of the environment around the quasar indicates the occurrence of a significant over-density of galaxies with a redshift compatible with z~0.4. This suggests that it resides in a moderately rich cluster of galaxies.