- [*] Internal Dynamics, Structure and Formation of Dwarf Elliptical
Galaxies: I. A Keck/HST Study of Six Virgo Cluster Dwarfs
- Geha M., Guhathakurta P., van der Marel R.P.
- AJ, 124, 3073-3087, 2002
this paper in the ADS
Spectroscopy with the Keck II 10-meter telescope and Echelle
Spectrograph and Imager is presented for six Virgo Cluster dwarf
elliptical (dE) galaxies in the absolute magnitude range M_V between
-15.7 and -17.2. The mean line-of-sight velocity and velocity
dispersion are resolved as a function of radius along the major axis
of each galaxy, nearly doubling the total number of dEs with
spatially-resolved stellar kinematics. None of the observed objects
shows evidence of strong rotation: upper limits on v/sigma, the ratio
of the maximum rotational velocity to the mean velocity dispersion,
are well below those expected for rotationally-flattened objects.
Such limits place strong constraints on dE galaxy formation models.
Although these galaxies continue the trend of low rotation velocities
observed in Local Group dEs, they are in contrast to recent
observations of large rotation velocities in slightly brighter cluster
dEs. Using surface photometry from Hubble Space Telescope Wide Field
Planetary Camera 2 images and spherically-symmetric dynamical models,
we determine global V-band mass-to-light ratios between 3 and 6.
These ratios are comparable to those expected for an old to
intermediate-age stellar population and are broadly consistent with
the observed V-I colors of the galaxies. This implies that these dEs
do not have a significant dark matter component inside an effective
radius. Central black holes more massive than approximately 10^7
solar masses are ruled out at the 99.9% confidence level. For the
five nucleated dEs in our sample, we determine kinematic and
photometric properties for the central nucleus separately from the
underlying host dE galaxy. These nuclei are as bright or brighter
than the most luminous Galactic globular clusters and lie near the
region of Fundamental Plane space occupied by globular clusters. In
this space, the Virgo dE galaxies lie in the same general region as
Local Group and other nearby dEs, although non-rotating dEs appear to
have a slightly higher mean mass and mass-to-light ratio than their
rotating counterparts; the dE galaxies occupy a plane parallel to, but
offset from, that occupied by normal elliptical galaxies.
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Last modified December 8, 2002.
Roeland van der Marel,