Hubble Space Telescope Imaging of the Active Dwarf Galaxy RGG 118

RGG 118 (SDSS 1523+1145) is a nearby (z = 0.0243), dwarf disk galaxy (M_∗ ≈ 2 × 10⁹M_⊙) that is found to host an active ∼50,000 solar mass black hole at its core. RGG 118 is one of a growing collective sample of dwarf galaxies known to contain active galactic nuclei (AGNs) - a group that, until recently, contained only a handful of objects. Here, we report on new Hubble Space Telescope Wide Field Camera 3 UVIS and IR imaging of RGG 118, with the main goal of analyzing its structure. Using 2D parametric modeling, we find that the morphology of RGG 118 is best described by an outer spiral disk, an inner component consistent with a pseudobulge, and a central point-spread function (PSF). The luminosity of the PSF is consistent with the central point source that is being dominated by the AGN. We measure the luminosity and the mass of the "pseudobulge" and confirm that the central black hole in RGG 118 is under-massive, with respect to the and relations. This result is consistent with a picture in which black holes in disk-dominated galaxies grow primarily through secular processes.