Hα photometry of Abell 2390 |
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| Authors: | Michael L Balogh †‡ Simon L Morris † |
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| Institution: | Department of Physics &Astronomy, University of Victoria, Victoria BC, V8X 4M6, Canada;Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council, 5071 West Saanich Road, Victoria BC, Canada V8X 4M6. |
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| Abstract: | We present the results of a search for strong H α emission line galaxies (rest frame equivalent widths greater than 50 Å) in the z ≈0.23 cluster Abell 2390. The survey contains 1189 galaxies over 270 arcmin2, and is 50 per cent complete at M r ≈?17.5+5 log h . The fraction of galaxies in which H α is detected at the 2 σ level rises from 0.0 in the central regions (excluding the cD galaxy) to 12.5±8 per cent at R 200. For 165 of the galaxies in our catalogue, we compare the H α equivalent widths with their O ii ] λ 3727 equivalent widths, from the Canadian Network for Observational Cosmology (CNOC1) spectra. The fraction of strong H α emission line galaxies is consistent with the fraction of strong O ii ] emission galaxies in the CNOC1 sample: only 2±1 per cent have no detectable O ii ] emission and yet significant (>2 σ ) H α equivalent widths. Dust obscuration, non-thermal ionization, and aperture effects are all likely to contribute to this non-correspondence of emission lines. We identify six spectroscopically 'secure' k+a galaxies W 0(O ii )<5 Å and W 0(H δ )?5 Å]; at least two of these show strong signs in H α of star formation in regions that are covered by the slit from which the spectra were obtained. Thus, some fraction of galaxies classified as k+a based on spectra shortward of 6000 Å are likely to be undergoing significant star formation. These results are consistent with a 'strangulation' model for cluster galaxy evolution, in which star formation in cluster galaxies is gradually decreased, and is neither enhanced nor abruptly terminated by the cluster environment. |
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| Keywords: | galaxies: clusters: individual: Abell 2390 galaxies: evolution |
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