Upper Limits on the Masses of 105 Supermassive Black Holes from Hubble Space Telescope/Space Telescope Imaging Spectrograph Archival Data

Abstract

Based on the modeling of the central emission-line width measured over subarcsecond apertures with the Hubble Space Telescope, we present stringent upper bounds on the mass of the central supermassive black hole, M _•, for a sample of 105 nearby galaxies (D < 100 Mpc) spanning a wide range of Hubble types (E-Sc) and values of the central stellar velocity dispersion, σ_c (58-419 km s^-1). For the vast majority of the objects, the derived M _• upper limits run parallel and above the well-known M _•-σ_c relation independently of the galaxy distance, suggesting that our nebular line-width measurements trace rather well the nuclear gravitational potential. For values of σ_c between 90 and 220 km s^-1, 68% of our upper limits falls immediately above the M _•-σ_c relation without exceeding the expected M _• values by more than a factor 4.1. No systematic trends or offsets are observed in this σ_c range as a function of the galaxy Hubble type or with respect to the presence of a bar. For 6 of our 12 M _• upper limits with σ_c <90 km s^-1, our line-width measurements are more sensitive to the stellar contribution to the gravitational potential, either due to the presence of a nuclear stellar cluster or because of a greater distance compared to the other galaxies at the low-σ_c end of the M _•-σ_c relation. Conversely, our M _• upper bounds appear to lie closer to the expected M _• in the most massive elliptical galaxies with values of σ_c above 220 km s^-1. Such a flattening of the M _•-σ_c relation at its high-σ_c end would appear consistent with a coevolution of supermassive black holes and galaxies driven by dry mergers, although better and more consistent measurements for σ_c and K-band luminosity are needed for these kinds of objects before systematic effects can be ruled out.

Based on observations with the NASA/ESA Hubble Space Telescope obtained at STScI, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.