Paper detail

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

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.