Rj. Harms et al., HST FOS SPECTROSCOPY OF M87 - EVIDENCE FOR A DISK OF IONIZED-GAS AROUND A MASSIVE BLACK-HOLE, The Astrophysical journal, 435(1), 1994, pp. 120000035
Using the Faint Object Spectrograph on the Hubble Space Telescope (HST
) to observe the central region of M87, we have obtained spectra cover
ing approximately 4600-6800 angstrom at a spectral dispersion approxim
ately 4.4 angstrom per resolution element through the 0''.26 diameter
entrance aperture. One spectrum was obtained centered on the nucleus o
f M87 and two centered 0''.25 off the nucleus at position angles of 21
-degrees and 201-degrees, thus sampling the anticipated major axis of
the disklike structure (described in a companion Letter) expected to l
ie approximately perpendicular to the axis of the M87 jet. Pointing er
rors for these observations are estimated to be less than 0''.02. Radi
al velocities of the ionized gas in the two positions 0''.25 on either
side of the nucleus are measured to be almost-equal-to +/- 500 km s-1
relative to the M87 systemic velocity. These observations plus emissi
on-line spectra obtained at two additional locations near the nucleus
show the ionized gas to be in Keplerian rotation about a mass M = (2.4
+/- 0.7) x 10(9) M(.) within the inner 0''.25 of M87. Our results pro
vide strong evidence for the presence of a supermassive nuclear black
hole in M87.