Michele Cappellari

Abstract:

We present high angular resolution (0.3 arcsec or 37 pc) Atacama Large Millimeter/submillimeter Array observations of the CO(2–1) line emission from a central disc in the early-type galaxy NGC 524. This disc is shown to be dynamically relaxed, exhibiting ordered rotation about a compact 1.3 mm continuum source, which we identify as emission from an active supermassive black hole (SMBH). There is a hole at the centre of the disc slightly larger than the SMBH sphere of influence. An azimuthal distortion of the observed velocity field is found to be due to either a position angle warp or radial gas flow over the inner 2. 5. By forward-modelling the observations, we obtain an estimate of the SMBH mass of 4.0+3.5 −2.0 × 108 M, where the uncertainties are at the 3σ level. The uncertainties are dominated by the poorly constrained inclination and the stellar mass-to-light ratio of this galaxy, and our measurement is consistent with the established correlation between SMBH mass and stellar velocity dispersion. Our result is roughly half that of the previous stellar dynamical measurement, but is consistent within the uncertainties of both. We also present and apply a new tool for modelling complex molecular gas distributions.

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, ${9.12}_{-1.53}^{+1.84}\times {10}^{5}$ M ⊙ and ${6.31}_{-2.74}^{+1.06}\times {10}^{5}$ 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 ${6.8}_{-6.7}^{+95.6}\times {10}^{3}$ 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 lesssim10−5 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.

Abstract:

Three basic ingredients are required to generate a simple stellar population (SSP) library, i.e. an initial mass function (IMF), a stellar evolution model/isochrones, and an empirical/theoretical stellar spectral library. However, there are still some uncertainties to the determination and understanding of these ingredients. We perform the spectral fitting to test the relative parameter offsets between these uncertainties using two different stellar population models, two different empirical stellar libraries, two different isochrones, and the Salpeter and Chabrier IMFs. Based on these setups, we select five SSP libraries generated with the Galaxev/STELIB and Vazdekis/MILES models, and apply them to the pPXF full-spectrum fitting of both MaNGA and mock spectra. We find that: (1) Compared to the Galaxev/STELIB model, spectral fitting qualities with the Vazdekis/MILES model have significant improvements for those metal-rich (especially oversolar) spectra, which cause better reduced χ 2 distributions and more precisely fitted absorption lines. This might due to the lack of metal-rich stars in the empirical STELIB library, or code improvement of the Vazdekis model. (2) When applying the Vazdekis/MILES model for spectral fitting, the IMF variation will lead to not only a systematic offset in M ∗ /L r , but also offsets in age and metallicity, and these offsets increase with increasing stellar population ages. However, the IMF variation caused metallicity offsets disappear in the case of Galaxev/STELIB based libraries. (3) The Padova2000 model provides a better match to the MaNGA galaxy spectra at [M/H] L < −1.0, while the BaSTI model match the local galaxy spectra better at [M/H] L > −1.0. Current tests suggest that spectral fitting with the Vazdekis/MILES + BaSTI combination would be a better choice for local galaxies.