Authors: Alister W. Graham, Bogdan C. Ciambur, Roberto Soria
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 (105 < Mbh/Msun < 107). How this extends into the realm of intermediate mass black holes (102 < Mbh < 105 ) is not yet clear, although for the barred Sm galaxy LEDA 87300, Baldassare et al. have recently reported a nominal virial mass Mbh=5x104 Msun residing in a `spheroid' of stellar mass equal to 6.3x108 Msun. We point out, for the first time, that LEDA 87300 therefore appears to reside on the near-quadratic Mbh-Msph,* 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 Mbulge=0.9x108 Msun, and Mbulge/Mdisk=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 (Mbh=2.9x104 Msun) and show that LEDA 87300 remains consistent with the Mbh-σ relation, and the near-quadratic Mbh-Msph,* 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.