Ultraviolet observations of galaxies in nearby clusters. I. Star formation rate in spiral galaxies of Abell 1367.
Abstract
We present, ultraviolet (λ = 2000 A) observations of a sample of 27 spiral galaxies member of the nearby cluster A1367, obtained with a 40 cm imaging telescope flown on a stabilized balloon-borne gondola. After correction for dust extinction, the observed ultraviolet fluxes are used to derive an estimate of the current star formation rate (SFR). These SFRs are compared with those derived for field galaxies in a previous UV survey. The star formation rates of A1367 spiral galaxies are in the range of those of field galaxies, and galaxies with exceptional star formation rate in regard to their H I content are not observed. In average, the H I surface densities and SFRs per unit area, obtained in dividing the HI gas masses and SFRs by the isophotal area of the galaxies, are lower in the cluster than in the field. Most of the cluster galaxies with low H I surface density (<= 3 10^20^ at/cm^2^) seem to have formed intermediate mass stars during the last, 10^8^ years. The lower values of the H I surface densities and SFRs per unit area found for A1367 galaxies can be in part explained if the ratio of the H I to optical diameter is lower and if the molecular gas (H_2_) is not depleted in the cluster galaxies. Using the SFR/M_H I_ ratio as a measure of star formation efficiency, we find that the star formation seems to be more efficient for galaxies in the central part of the cluster than for galaxies in the outer part or field galaxies. In average the H I- deficient galaxies of our sample appear more efficient to form stars than normal galaxies. This trends are reduced and the environmental effects on the star formation efficiency become hardly significant if H 2 is not depleted in A1367 galaxies.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- August 1990
- Bibcode:
- 1990A&A...235...60D
- Keywords:
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- Galactic Clusters;
- Spiral Galaxies;
- Star Formation Rate;
- Ultraviolet Astronomy;
- Active Galaxies;
- Brightness Distribution;
- Hydrogen;
- Molecular Gases;
- Stellar Mass;
- Astrophysics