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Title:
Rotation Curves and Velocity Measures for Spiral Galaxies in Pairs
Authors:
Keel, William C.
Publication:
Astrophysical Journal Supplement v.106, p.27 (ApJS Homepage)
Publication Date:
09/1996
Origin:
APJ; NED
ApJ Keywords:
GALAXIES: DISTANCES AND REDSHIFTS, GALAXIES: KINEMATICS AND DYNAMICS, GALAXIES: SEYFERT, GALAXIES: SPIRAL
DOI:
10.1086/192326
Bibliographic Code:
1996ApJS..106...27K

Abstract

Rotation curves have been obtained for 76 spiral galaxies in pairs, including a geometrically selected subset from the Karachentsev catalog and a set of Seyfert galaxies with close companions. Derived parameters of the rotation curves and the galaxies light distributions are also presented. The rotation curves are classified broadly by shape, with special emphasis on kinematic disturbances and regions of solid-body behavior that may lead to bar development. Broadband images of the galaxies allow assessments of their degree of symmetry or disturbance. These velocity slices afford an empirical basis for evaluating the accuracy of radial velocity measures for spiral galaxies in pairs, and the dynamically important radial velocity differences. Specifically, the disagreement among several plausible ways of estimating the central velocity from these rotation data is used to estimate how closely any of these might approximate the nuclear or center-of-mass values. From seven indicators of central velocity, the internal scatter is σ_vv_ = 34 km s^-1^. Of these, the velocity weighted by Hα intensity along the slit shows a systematic offset of about 20 km s^-1^ with respect to the others for the Karachentsev pairs, in the sense that this measure is redshifted with respect to the other indicators. This is in the sense (but not of the total magnitude) required to account for statistical asymmetries in pair velocity differences. Individual scatter between the velocity indicators taken pairwise ranges from σ = 20 to 52 km s^- 1^. These results imply that emission-line data such as these cannot specify the center of mass or nuclear redshift at a level more accurate than this, even for arbitrarily precise velocity measurements, because it is not clear how the observed quantities relate to the desired measurement in a physical sense. No useful predictor of which galaxies have large or small scatter among velocity measures was found, except that the scatter is small for the class of "nonrotating" galaxies with small overall velocity amplitudes. Projected separation, separation normalized to disk scale length, and morphological disturbance do not correlate with the velocity scatter.

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