Mathematics – Logic
Scientific paper
Aug 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aj....106..473c&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 106, no. 2, p. 473-492, 806.
Mathematics
Logic
164
Absorption Spectra, Astronomical Spectroscopy, Spatial Distribution, Spiral Galaxies, Star Clusters, Star Formation, Balmer Series, Coma, Red Shift
Scientific paper
We have obtained multifiber spectra of 125 early-type galaxies in the Coma cluster of galaxies, using the Hydra bench spectrograph on the 4m telescope at Kitt Peak. The sample selection was based on both color and morphology, care being taken to exclude intermediate and late-type spirals. Surprisingly, a large fraction (about 1/3) of all galaxies in a field located approximately 40 arcmin SW of the center of the cluster exhibits enhanced Balmer absorption lines or emission lines, indicative of recent star formation or nuclear activity. In contrast, very few such galaxies are found in the central field of the cluster. Those galaxies with abnormal spectra cover a range in luminosity down to B ≈ 19 (MB ≈ -15). Furthermore, the bulk of the abnormal spectrum galaxies are located near a secondary peak in the cluster X-ray emission found by Briel et.al. (A&A, 259, L31,1992) and by Watt et.al. (MNRAS, 258, 738, 1992). We argue by detailed comparisons with Kennicutt's (ApJS, 79, 255, 1992) sequence of normal spiral galaxy spectra that the anomalous spectral features cannot arise from morphological misindentifications. Specifically, the abnormal spectra are fundamentally different, with [O II] emission lines too weak for the enhanced Balmer absorption. The spectra are, however, remarkably similar to the red Hδ-strong galaxies studied by Couch & Sharples (MNRAS, 229, 423, 1987) in clusters at redshift z ≈ 0.3. Hence it appears that an environmental process similar to that frequently found in clusters at moderate redshift is occurring at the present epoch in the outskirts of the Coma cluster.
Bower Richard G.
Caldwell Nelson
Ellis Richard S.
Rose James A.
Sharples Ray M.
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