- [*] Improved evidence for a black hole in M32 from HST/FOS spectra -
- van der Marel R.P., de Zeeuw P.T., Rix H.W.
- ApJ, 488, 119-135, 1997
- © 1997. The American Astronomical Society.
All Rights Reserved.
this paper in the ADS
We have obtained spectra through small apertures centered on the
nuclear region and major axis of M32, with the Faint Object
Spectrograph (FOS) on the Hubble Space Telescope (HST). A detailed
analysis and reduction of the data is presented, including: (i) new
calibrations and modeling of the FOS aperture sizes,
point-spread-function and line-spread-functions; (ii) determination of
the aperture positioning for each observation from the observed count
rate; and (iii) accurate wavelength calibration, template matching,
and kinematical analysis of the spectra. This yields measurements of
the stellar rotation velocities and velocity dispersions near the
center of M32, with five times higher spatial resolution than the best
available ground-based data. The inferred velocities provide the
highest angular resolution stellar kinematical data obtained to date
for any stellar system.
The HST observations show a steeper rotation curve and higher central
velocity dispersion than the ground-based data. The rotation velocity
is observed to be 30 km/s at 0.1 arcsec from the nucleus. This is
roughly twice the value measured from the ground at this distance. The
nuclear dispersion measured through the smallest FOS aperture (0.068
arcsec square) is 156 +/- 10 km/s. The average of four independent
dispersion measurements at various positions inside the central 0.1
arcsec is 126 km/s, with a RMS scatter of 21 km/s. The nuclear
dispersion measured from the ground is only 85-95 km/s, whereas the
dispersion outside the central arcsec is only 45-55 km/s. These
results significantly strengthen previous arguments for the presence
of a massive nuclear black hole in M32. Detailed dynamical models are
presented in a companion paper.
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Roeland van der Marel,