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 (10⁵ < M_bh/M_⊙ ≲ 10⁷). How this extends into the realm of intermediate-mass black holes (10² < M_bh/M_⊙ < 10⁵) is not yet clear, although for the barred Sm galaxy LEDA 87300, Baldassare et al. recently reported a nominal virial mass of M_bh = 5 × 10⁴ M_⊙ residing in a "spheroid" of stellar mass equal to 6.3 × 10⁸ M_⊙. 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. modeled 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 = 0.9 × 10⁸ M_⊙ 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⁻¹) and black hole mass ($M_{bh}={2.9}_{-2.3}^{+6.7}\times {10}^4{f}_{2.3}{M}_{\odot }$) and show that LEDA 87300 remains consistent with the M_bh–σ relation, and also 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.