Does the intermediate mass black hole in LEDA 87300 (RGG 118) follow the near-quadratic (M_bh)-(M_spheroid) relation?

TL;DR

This study confirms that the intermediate mass black hole in LEDA 87300 follows a near-quadratic relation with its host spheroid, supporting models of rapid black hole growth in low-mass galaxies.

Contribution

It provides a detailed bulge+bar+disk decomposition of LEDA 87300, revises its black hole and bulge mass estimates, and demonstrates its consistency with the near-quadratic M_bh-M_sph relation.

Findings

LEDA 87300's black hole aligns with the near-quadratic M_bh-M_sph relation.

Revised bulge luminosity is 7.7 times fainter than previous estimates.

Black hole mass and velocity dispersion are consistent with established relations.

Abstract

The mass scaling relation between supermassive black holes and their host spheroids has previously been described by a quadratic or steeper relation at low masses (10^5 < M_bh/M_sun < 10^7). How this extends into the realm of intermediate mass black holes (10^2 < M_bh/M_sun < 10^5) is not yet clear, although for the barred Sm galaxy LEDA 87300, Baldassare et al. have recently reported a nominal virial mass M_bh=5x10^4 M_sun residing in a `spheroid' of stellar mass equal to 6.3x10^8 M_sun. We point out, for the first time, that LEDA 87300 therefore appears to reside on the near-quadratic M_bh-M_{sph,*} relation. However, Baldassare et al. modelled the bulge _and_ bar as the single spheroidal component of this galaxy. Here we perform a 3-component bulge+bar+disk decomposition and find a bulge luminosity which is 7.7 times fainter than the published `bulge' luminosity. After correcting for dust we find that M_bulge=0.9x10^8 M_sun, and M_bulge/M_disk=0.04 - which is now in accord with ratios typically found in Scd-Sm galaxies. We go on to discuss slight revisions to the stellar velocity dispersion (40+/-11 km/s) and black hole mass (M_bh=2.9x10^4 M_sun) and show that LEDA 87300 remains consistent with both the M_bh-sigma relation and the near-quadratic M_bh-M_{sph,*} relation when using the reduced bulge mass. LEDA 87300 therefore offers the first support for the rapid but regulated (near-quadratic) growth of black holes, relative to their host bulge/spheroid, extending into the domain of intermediate mass black holes.