HUBBLE-SPACE-TELESCOPE SPECTROSCOPIC EVIDENCE FOR A1X10(9)M(CIRCLE-DOT) BLACK-HOLE IN NGC-4549

The discovery by Kormendy of a M .similar or equal to 10(9) M. massive dark object (MDO) in NGC 4594 is confirmed with higher resolution spe ctroscopy from the Canada-France-Hawaii Telescope (CFHT) and the Hubbl e Space Telescope (HST). CFHT measurements with the Subarcsecond Imagi ng Spectrograph improve the resolution from sigma=0.''.40 to 0.'' 27 Gaussian dispersion radius of the point-spread function (PSF). The app arent central velocity dispersion rises from sigma=250+/-7 km s(-1) to sigma=286+/-7 km s(-1). As observed with the COSTAR-corrected HST, th e Faint Object Spectrograph, and a 0.'' 21 aperture, sigma=321+/-7 km s(-1) is still higher, and the central rotation curve is very steep. T he highest-M . published dynamical model fits the new observations rea sonably well when ''observed'' at HST resolution. The spatial resoluti on has now improved by a factor of similar to 5 since the discovery me asurements, and the case for a black hole (BH) has strengthened corres pondingly. We confirm that NGC 4594 has a Seyfert spectrum; Her is sim ilar to 5200 km s(-1) wide at zero intensity. However, gas velocities are lower than the circular velocities implied by the stars, so they c annot be used to test the BH case in NGC 4594. The gas may be in a rin g, or it may be associated with patchy dust. HST images with the Wide Field and Planetary Camera 2 show dust at some aperture positions. NGC 4594 appears to have a bright point nucleus. However, the central abs orption-line strengths are low, consistent with dilution by enough non thermal light to explain the ''nucleus.'' There is no evidence for a d istinct nuclear star cluster. NGC 4594 is similar to M87, which also h as a nonthermal nuclear source, and not to M31 and NGC 3115, which hav e quiescent BHs and nuclear star clusters.