The host galaxy of OJ 287 revealed by optical and near-infrared imaging

TL;DR

This study used high-resolution optical and near-infrared imaging to detect and analyze the host galaxy of the BL Lac object OJ 287, revealing its properties and the overmassive nature of its central black hole.

Contribution

First detection of the host galaxy of OJ 287 in deep i-band and K-band images, providing new insights into its luminosity and black hole mass relation.

Findings

Host galaxy is an early type galaxy with typical luminosity.

Central black hole is overmassive relative to the host galaxy.

Host galaxy properties align with the distribution of BL Lac objects.

Abstract

The BL Lacertae object OJ 287 (z = 0.306) has unique double-peaked optical outbursts every ~12 years, and it presents one of the best cases for a small-separation binary supermassive black hole (SMBH) system, with an extremely massive primary log (M_BH/M_Sun) ~ 10.3. However, the host galaxy is unresolved or only marginally detected in all optical studies so far, indicating a large deviation from the bulge mass - SMBH mass relation. We have obtained deep, high spatial resolution i-band and K-band images of OJ~287 when the target was in a low state, which enable us to detect the host galaxy. We find the broad-band photometry of the host to be consistent with an early type galaxy with M_R = -22.5 and M_K = -25.2, placing it in the middle of the host galaxy luminosity distribution of BL Lacertae objects. The central supermassive black hole is clearly overmassive for a host galaxy of that luminosity, but not unprecedented, given some recent findings of other ``overmassive'' black holes in nearby galaxies.