Astronomy and Astrophysics – Astronomy
Scientific paper
May 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...184.4804e&link_type=abstract
American Astronomical Society, 184th AAS Meeting, #48.04; Bulletin of the American Astronomical Society, Vol. 26, p.938
Astronomy and Astrophysics
Astronomy
1
Scientific paper
A small fraction of S0 galaxies are surrounded by delicate rings of gas, dust, and stars nearly perpendicular to the plane of the galaxy disk. As these polar rings are typically quite blue, HI rich, and show signs of dust and Hα emission (see Whitmore et al., 1990 AJ 100 1489), they are generally believed to be debris from the accretion of a dwarf Irregular (dI) galaxy by the S0. While a great deal of work has been devoted to understanding the dynamics of polar rings (e.g., Steiman-Cameron & Durisen 1988 ApJ 325 26; Sackett & Sparke 1990 ApJ 361 408), very little attention has been paid to the properties of the rings themselves. The prevalence of Hα emission from polar rings convinced us that it would be possible to determine the abundances of the ring material from nebular spectrophotometry and thus test the assertion that the ring material is accreted from a metal-poor dI galaxy. We present the results of this work for the prototype polar-ring galaxy NGC 2685. Long-slit spectrophotometry of a number of HII regions in the polar ring of NGC 2685 were obtained with the 2.7m telescope at the McDonald Observatory, and with the MMT. Spectral coverage encompasses all relevant diagnostic lines from [OII] 3727 Angstroms to [SII] 6731 Angstroms at sufficient spectral resolution to clearly resolve all close line-pairs. Because [OIII] 4363 Angstroms is not visible in our spectra, we have had to use the semi-empirical calibration of Edmunds and Pagel (1984 MNRAS 211 507) to derive oxygen abundances. Although oxygen abundances based on this method are potentially uncertain by up to a factor of two, the abundances we determine are ~ Solar for the HII regions in the polar ring of NGC 2685; much higher than those found for any dI galaxy. If this result holds for all polar rings, it will provide a strong constraint for models of the formation and evolution of these systems. We are continuing this research by obtaining Hα imaging and subsequent spectrophotometric data for a sample of kinematically confirmed polar-ring galaxies.
Eskridge Paul B.
Pogge Richard W.
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