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Session 54 - Spiral Galaxy Kinematics.
Oral session, Tuesday, January 14
Harbour B,

[54.04] The Ursa Major Cluster of Galaxies: TF-relations and Dark Matter in Spirals

M. A. W. Verheijen, R. Sancisi (Kapteyn Inst., The Netherlands)

I will present some results from my thesis research on the scatter in the Tully-Fisher relations and the Dark Matter content of spiral galaxies as a function of morphology, luminosity etc., making use of detailed photometric and kinematic information of galactic disks.

A volume limited sample of 79 galaxies was selected from the spiral rich currently forming Ursa Major cluster which has a low velocity dispersion of only \approx150 km s^-1. Since the cluster members are nearly equidistant, there is little doubt about their relative sizes, luminosities and masses.

The entire complete (M_B<-16) sample of 62 galaxies has been imaged in the B, R, I and K^\prime passbands. Westerbork 21cm-line HI synthesis observations have been obtained for 65 galaxies yielding HI column density maps and galactic velocity fields from which kinematic inclinations and rotation curves could be derived for many systems.

A comparison with spirals in Virgo and the field shows that the cluster environment has no influence on the global HI properties of the Ursa Major spirals. I will present a strong indication for a possible bimodality in the surface brightness distributions.

Various luminosity and kinematic measures are considered. It will be shown that for a `kinematic healthy' subsample of 17 spirals with well behaved circular rotation, the scatter in the TF relations is minimized when using K^\prime luminosities and Log(2V_flat) with V_flat the amplitude of the flat part of the rotation curve. Given the measurement uncertainties and the possible depth of the sample, the total observed scatter is consistent with no intrinsic scatter.

Finally, I will present mass-to-light ratios of the stellar populations derived from decomposing the rotation curves into their dynamical constituents assuming a maximum disk.

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Program listing for Tuesday