[ITAL]Hubble Space Telescope[/ITAL] Spectroscopic Evidence for a 1 × 10[TSUP]9[/TSUP] [ITAL]M[/ITAL][TINF]⊙[/TINF] Black Hole in NGC 4594

Abstract

The discovery by Kormendy of a M• ≃ 109 M☉ massive dark object (MDO) in NGC 4594 is confirmed with higher resolution spectroscopy from the Canada-France-Hawaii Telescope (CFHT) and the Hubble Space Telescope (HST). CFHT measurements with the Subarcsecond Imaging Spectrograph improve the resolution from σ* = 040 to 027 Gaussian dispersion radius of the point-spread function (PSF). The apparent central velocity dispersion rises from σ = 250 ± 7 km s-1 to σ = 286 ± 7 km s-1. As observed with the COSTAR-corrected HST, the Faint Object Spectrograph, and a 021 aperture, σ = 321 ± 7 km s-1 is still higher, and the central rotation curve is very steep. The highest-M• published dynamical model fits the new observations reasonably well when "observed" at HST resolution. The spatial resolution has now improved by a factor of ~5 since the discovery measurements, and the case for a black hole (BH) has strengthened correspondingly.