Is There a Black Hole in NGC 4382?

Abstract

We present Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph observations of the galaxy NGC 4382 (M85) and axisymmetric models of the galaxy to determine mass-to-light ratio ( ##IMG## [http://ej.iop.org/icons/Entities/Upsi.gif] {Upsilon} V ) and central black hole mass ( M BH ). We find ##IMG## [http://ej.iop.org/icons/Entities/Upsi.gif] {Upsilon} V = 3.74 ± 0.1 M _ / L _ and M BH = 1.3 +5.2 – 1.2 _ 10 7 M _ at an assumed distance of 17.9 Mpc, consistent with no black hole. The upper limit, M BH < 9.6 _ 10 7 M _ (2_) or M BH < 1.4 _ 10 8 (3_), is consistent with the current M -_ relation, which predicts M BH = 8.8 _ 10 7 M _ at _ e = 182 km s –1 , but low for the current M - L relation, which predicts M BH = 7.8 _ 10 8 M _ at L V = 8.9 _ 10 10 L _, V . HST images show the nucleus to be double, suggesting the presence of a nuclear eccentric stellar disk, analogous to the Tremaine disk in M31. This conclusion is supported by the HST velocity dispersion profile. Despite the presence of this non-axisymmetric feature and evidence of a recent merger, we conclude that the reliability of our black hole mass determination is not hindered. The inferred low black hole mass may explain the lack of nuclear activity.