Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986apj...305..136c&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 305, June 1, 1986, p. 136-147.
Astronomy and Astrophysics
Astrophysics
50
Elliptical Galaxies, Galactic Rotation, Gas Dynamics, Stellar Motions, Astronomical Spectroscopy, Dark Matter, Emission Spectra, Mass Distribution, Mass To Light Ratios, Oxygen Ions, Star Distribution, Velocity Distribution
Scientific paper
The E4 galaxy NGC 7097 is normal on broad-band photographs, and has the surface-brightness profile of an ordinary elliptical galaxy. Spectra taken at the CTIO 4 m telescope show that NGC 7097 has extended O II and O III forbidden line emission, which provides an unusual opportunity to use the motion of the gas to probe the radial mass distribution of an elliptical galaxy. These observations are consistent with a centrally concentrated gas disk of 4-kpc radius, inclined at 60 deg to the plane of the sky. If the gas velocities are circular, they can be used to determine M(r) for this galaxy. The inferred mass distribution of the galaxy has a larger scale length than the scale length of the stellar distribution, so that the mass-to-light ratio increases from below 1 at the center to 3.5 at 3 kpc. In the absence of a variation in the stellar composition, this is evidence for dark matter in an elliptical galaxy. Analysis of stellar rotation and velocity dispersion distributions through linear programming methods shows that, to match the observed mass and light distributions, the radial component of the stellar velocity dispersions must be larger than the tangential dispersions.
Caldwell Nelson
Kirshner Robert P.
Richstone Douglas O.
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