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Date and Time of the Query: 2019-06-26 T03:00:28 PDT
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For refcode 1989ApJ...344..171K:
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Copyright by American Astronomical Society. Reproduced by permission
1989ApJ...344..171K THE EFFECTS OF ENVIRONMENT ON THE MOLECULAR AND ATOMIC GAS PROPERTIES OF LARGE VIRGO CLUSTER SPIRALS JEFFREY D. P. KENNEY AND JUDITH S. YOUNG Five College Radio Astronomy Observatory, University of Massachusetts Received 1988 September 21; accepted 1989 February 10 ABSTRACT The molecular and atomic gas properties of 40 Virgo cluster spiral galaxies are compared with optical properties order to assess the effect of the Virgo environment on the interstellar media of Virgo disks. The dependency of CO emission on galaxy mass and morphological type are first examined so that the effects of environment can be distinguished from those of mass and morphology. Virgo Sc galaxies fainter than B^0^_T_ = 12 are discovered to have significantly weaker CO emission per unit mass than those brighter than B^0^_T_ = 12 and are excluded from our environmental analysis. Among Virgo galaxies brighter than B^0^_T_ = 11, Sa-Sb galaxies have slightly weaker CO emission per unit mass than Sc galaxies and are therefore analyzed separately from the Sc's in the environmental study. Galaxies shown by others to be significantly H I-deficient have systematically larger ratios of CO flux to H I flux. With one exception, the spatial distributions of CO emission appear normal in the H I-deficient spirals. Large Sc galaxies which are H I-deficient by a factor of 10 are gas-deficient by only a factor of ~2-3, due to the survival of large amounts of molecular gas. The results for the large Sab-Sb galaxies are similar, although less certain due to the paucity of early-type Virgo spirals with normal H I emission. The total gas - deficiency may be comparable to the H I deficiency in the galaxies fainter than B^0^_T_ = 12, since these galaxies have weak CO emission, and probably have a smaller fraction of their interstellar media in the molecular phase. Comparison of the radial distributions of H I and H2 indicate that the total gas deficiency is manifested largely by a lack of H I in the outer disk. The inner disk regions, although moderately H I-deficient, are not significantly gas-deficient since the interstellar media in the inner regions of most of the galaxies in the sample are H2-dominated. The massive star formation rates, as traced by H{alpha} line emission, are also lower by factors of ~2-3 in Sc galaxies which are H I-deficient by a factor of 10. We conclude that the massive star formation rate in H I- deficient spirals is reduced by an amount comparable to the total gas deficiency, although this may be in part fortuitous, since gas is lost mostly from the outer galaxy where relatively fewer massive stars form. The lower H I surface densities in the inner disk regions may result from either the selective stripping of low column density gas, or from a reduced H_2_ dissociation rate which is expected from the smaller numbers of massive stars. Subject headings: galaxies: abundances - galaxies: clustering - galaxies: interstellar matter - interstellar: molecules - stars: formation
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