Deidre Ann Hunter

Optical properties and dynamics of galaxies in the Hickson compact groups

Broad-band R images, Hα images, and Hα long-slit spectroscopy for a set of galaxies in 21 Hickson compact groups are presented. Some of the galaxies are tidally interacting and distorted; some appear morphologically normal. Observed velocity patterns range from too peculiar to form rotation curves (one-third of spiral sample), to abnormal (one-third), to normal (one-third); peculiar rotation curves are only loosely coupled with peculiar morphology. For individual galaxies, values of integral M/L B are low, slightly lower than for field spirals of equivalent Hubble type. All of these observations support a model in which the compact group galaxies have only recently accumulated from the lumpy general galaxy distribution, and which tidal interactions are frequent and ongoing.

One galaxy from several - The Hickson compact group H31

The compact group H31 was identified by Hickson in 1982; it consists of four galaxies in close proximity, at least two of which (A and C) are interacting. Red and H-alpha frames and long-slit spectroscopy identify at least three other close members of the group; an H I envelope encloses all galaxies. Nuclear spectra of galaxies A and C show velocity patterns characteristic of interacting galaxies as well as the broad 4650 A feature indicative of W-R stars. These features reveal that large numbers of massive stars formed more than 10 exp 6.5 yr ago. Other observed characteristics all suggest that H31 is in the process of merging to a single galaxy. H31 thus supports computations which indicate that galaxies in compact groups merge to form a single remnant. 52 refs.

Optical rotation velocities and images of the spiral galaxy NGC 3198

H-alpha rotation velocities obtained from an echelle spectrogram to a radius of 2 arcmin for the spiral galaxy NGC 3198 agree well with the 21 cm rotation velocities of van Albada et al. (1985). The rotation curve is typical of Sc type galaxies in spite of NGC 3198s extended H I disk. From optical R and H-alpha-emission images, used to search for star-forming regions in the outer parts of this galaxy, several H-alpha knots are identified as far out as the Holmberg radius. With increasing radial distance out to 2 arcmin, the R-band surface brightness falls, the H-alpha is approximately constant, and the H I surface brightness rises. 27 references.