Velocity dispersions in the bulges of spiral and S0 galaxies. II Further observations and a simple three-component model for spiral galaxies

Details Velocity dispersions in the bulges of spiral and S0 galaxies. II Further observations and a simple three-component model for spiral galaxies Velocity dispersions in the bulges of spiral and S0 galaxies. II Further observations and a simple three-component model for spiral galaxies

Nov 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981apj...250...43w&link_type=abstract

Astrophysical Journal, Part 1, vol. 250, Nov. 1, 1981, p. 43-54. Research supported by the Alfred P. Sloan Foundation.

Astronomy and Astrophysics

Astrophysics

69

Astronomical Models, Dispersions, Elliptical Galaxies, Galactic Nuclei, Galactic Structure, Spiral Galaxies, Galactic Rotation, Luminosity, Tables (Data), Virgo Galactic Cluster

Scientific paper

We have obtained velocity dispersions for 24 galaxies in the Virgo cluster to supplement our earlier results. A 2000 channel intensified Reticon scanner has again been used on the 1.3 m telescope of McGraw-Hill Observatory, and a Fourier quotient technique has been employed to yield dispersions. We have confirmed our earlier result that spiral bulges exhibit a relation between total luminosity and velocity dispersion with the form L ∝ σ4, but with velocity dispersions that are 17 ± 8% smaller than elliptical galaxies at the same absolute magnitude. However, possible systematic errors may still affect the reality of this gap. The scatter in the L ∝ σ4 relationship is substantially larger for the spiral bulges than for the elliptical galaxies. This larger scatter probably indicates that spiral bulges comprise a more heterogeneous sample than do elliptical galaxies. We also find that the bulge components of SO galaxies follow a L ∝ σ4 relation with no gap with the ellipticals. The similarity in this relation for the spheroidal components of spiral, SO, and elliptical galaxies indicates that the systems are dynamically similar.
We have compared our velocity dispersions with rotational velocities determined from neutral hydrogen widths. For a totally bulge dominated spiral the ratio of the asymptotic rotational velocity to the velocity dispersion is about 1.4. This suggests that the mass responsible for producing the flat rotation curves (presumably the "halo") resides in a spheroidal component rather than in the disk. Our study also substantiates our earlier result that the massive halo is not merely an extension of the bulge, but is a separate dynamical component for most of our galaxies. A simple three-component model has been constructed to aid in the interpretation of this data. These models provide an independent indication of the existence of massive halos in spiral galaxies.

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