The Low End of the Supermassive Black Hole Mass Function: Constraining the Mass of a Nuclear Black Hole in Ngc 205 via Stellar Kinematics

Hubble Space Telescope (HST) images and spectra of the nucleated dwarf elliptical galaxy NGC 205 are combined with 3-integral axisymmetric dynamical models to constrain the massMBH of a putative nuclear black hole. This is only the second attempt, after M33, to use resolved stellar kinematics to search for a nuclear black hole with mass below 10 solar masses. We are unable to identify a best-fit value of MBH in NGC 205; however, the data impose a upper limit of 2.2×10M⊙ (1σ confidence) and and upper limit of 3.8× 10M⊙ (3σ confidence). This upper limit is consistent with the extrapolation of the MBH − σ relation to the MBH < 10M⊙ regime. If we assume that NGC 205 and M33 both contain nuclear black holes, the upper limits on MBH in the two galaxies imply a slope of ∼ 5.5 or greater for the MBH − σ relation. We use our 3-integral models to evaluate the relaxation time and stellar collision time in NGC 205; Tr is ∼ 10 yr or less in the nucleus and Tcoll ≈ 10 yr. The low value of Tr is consistent with core collapse having already occurred, but we are unable to draw conclusions from nuclear morphology about the presence or absence of a massive black hole. Subject headings: galaxies: elliptical and lenticular — galaxies: structure — galaxies: nuclei — stellar dynamics