Abstract
Abstract We improve the dynamical black hole (BH) mass estimates in three nearby low-mass early-type galaxies: NGC 205, NGC 5102, and NGC 5206. We use new Hubble Space Telescope (HST)/STIS spectroscopy to fit the star formation histories of the nuclei in these galaxies, and use these measurements to create local color–mass-to-light ratio (M/L) relations. We then create new mass models from HST imaging and combined with adaptive optics kinematics, we use Jeans dynamical models to constrain their BH masses. The masses of the central BHs in NGC 5102 and NGC 5206 are both below one million solar masses and are consistent with our previous estimates, M ⊙ and M ⊙ (3σ errors), respectively. However, for NGC 205, the improved models suggest the presence of a BH for the first time, with a best-fit mass of M ⊙ (3σ errors). This is the least massive central BH mass in a galaxy detected using any method. We discuss the possible systematic errors of this measurement in detail. Using this BH mass, the existing upper limits of both X-ray, and radio emissions in the nucleus of NGC 205 suggest an accretion rate ≲10−5 of the Eddington rate. We also discuss the color–M/L eff relations in our nuclei and find that the slopes of these vary significantly between nuclei. Nuclei with significant young stellar populations have steeper color–M/L eff relations than some previously published galaxy color–M/L eff relations.
Highlights
Observational efforts over the last two decades have revealed that every massive galaxy (M 1011M ) contains a central supermassive black hole (SMBH, MSMBH 106M ) at its center (e.g., Kormendy & Ho 2013; Saglia et al 2016)
We presented a new analysis of three nearby earlytype galactic nuclei: NGC 205, NGC 5102, and NGC 5206
We used stellar population fits to Hubble Space Telescope (HST)/STIS spectroscopy across the nucleus in combination with HST imaging to create color–mass-to-light ratio (M/L) relations and improve the mass models and BH mass estimates for the entire sample of galaxies
Summary
Observational efforts over the last two decades have revealed that every massive galaxy (M 1011M ) contains a central supermassive black hole (SMBH, MSMBH 106M ) at its center (e.g., Kormendy & Ho 2013; Saglia et al 2016). Due to the small fraction of all low-mass galaxies with identifiable AGN (and the difficulty in measuring the masses of SMBHs in detected AGN), these small number of dynamical measurements in the nearest systems still provide our best information on how BHs populate host galaxies. We use new HST /STIS spectroscopy and ACS/HRC (NGC 205), WFC3 (NGC 5102), and WFPC2 (NGC 5206) imaging to quantify the spatial variations in their nuclei M/Leff based on colors and specific star formation histories (SFHs) throughout their nuclei and improve their BH mass estimates using the Gemini/NIFS (NGC 205) and VLT/SINFONI (NGC 5102 and NGC 5206) kinematic data.
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