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The morphology and stellar populations of the dwarf amorphous galaxies NGC 216 and NGC 2915

Published online by Cambridge University Press:  07 August 2017

Gerhardt R. Meurer
Affiliation:
Anglo-Australian Observatory P.O. Box 296, Epping NSW, 2121 Australia
Glen Mackie
Affiliation:
Department of Astronomy University of Wisconsin 475 N. Charter St. Madison, WI 53706 U.S.A.

Abstract

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The definitions of the amorphous and blue compact dwarf (BCD) classes of galaxies are very similar. One key difference is that BCDs are often selected for their apparent compactness (i.e. a small angular size), which selects against nearby objects, whereas amorphous galaxies must be extended. We present initial results of a project to determine the population distribution in dwarf (MB < −18) amorphous galaxies (dAgs) and determine which dAgs can be classified as BCDs. We have used the 3.9m Anglo-Australian Telescope to obtain deep B and R CCD images of two dAgs: NGC 216 (MB = −17.3) and NGC 2915 (MB = −14.1). The morphology of NGC 216 is that of a dusty late-type edge-on disk galaxy, with a peculiar one-sided bar. It would not be classified as a BCD if seen face-on. However, NGC 2915 does have all the properties of a BCD, and can be classified so. It has numerous condensations near its center. Many of these are likely to be individual stars. We derive a distance to NGC 2915 of 5 Mpc if the brightest blue non-extended objects are blue supergiants, and if there is little internal extinction. Similar condensations are seen in the dAgs NGC 1705 (Meurer, et al., 1989. Astrophys. Space Sci., 156: 141) and NGC 5253 (Caldwell and Phillips, 1989. Astrophys. J., 338: 789) which are also likely to be BCDs.

Type
Poster Papers
Copyright
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