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

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.