Volume 543, July 2012
|Number of page(s)||31|
|Published online||22 June 2012|
The influence of the cluster environment on the star formation efficiency of 12 Virgo spiral galaxies ⋆
1 CDS, Observatoire astronomique, UMR 7550, 11 rue de l’université, 67000 Strasbourg, France
2 CSIRO Astronomy & Space Science, Epping, NSW 1710, Australia
3 Univ. Bordeaux, Laboratoire d’Astrophysique de Bordeaux, UMR 5804, 33270 Floirac, France
4 CNRS, LAB, UMR 5804, 33270 Floirac, France
5 Department of Astronomy and Yonsei University Observatory, Yonsei University, Republic of Korea
6 Yale University Astronomy Department, PO Box 208101, New Haven, CT 06520-8101, USA
Received: 20 December 2011
Accepted: 28 March 2012
The influence of the environment on gas surface density and star formation efficiency of cluster spiral galaxies is investigated. We extend previous work on radial profiles by a pixel-to pixel analysis looking for asymmetries due to environmental interactions. The star formation rate is derived from GALEX UV and Spitzer total infrared data based on the 8, 24, 70, and 160 μm data. As in field galaxies, the star formation rate for most Virgo galaxies is approximately proportional to the molecular gas mass. Except for NGC 4438, the cluster environment does not affect the star formation efficiency with respect to the molecular gas. Gas truncation is not associated with major changes in the total gas surface density distribution of the inner disk of Virgo spiral galaxies. In three galaxies (NGC 4430, NGC 4501, and NGC 4522), possible increases in the molecular fraction and the star formation efficiency with respect to the total gas, of factors of 1.5 to 2, are observed on the windward side of the galactic disk. A significant increase of the star formation efficiency with respect to the molecular gas content on the windward side of ram pressure-stripped galaxies is not observed. The ram-pressure stripped extraplanar gas of 3 highly inclined spiral galaxies (NGC 4330, NGC 4438, and NGC 4522) shows a depressed star formation efficiency with respect to the total gas, and one of them (NGC 4438) shows a depressed rate even with respect to the molecular gas. The interpretation is that stripped gas loses the gravitational confinement and associated pressure of the galactic disk, and the gas flow is diverging, so the gas density decreases and the star formation rate drops. We found two such regions of low star formation efficiency in the more face-on galaxies NGC 4501 and NGC 4654 which are both undergoing ram pressure stripping. These regions show low radio continuum emission or unusually steep radio spectral index. However, the stripped extraplanar gas in one highly inclined galaxy (NGC 4569) shows a normal star formation efficiency with respect to the total gas. We propose this galaxy is different because it is observed long after peak pressure, and its extraplanar gas is now in a converging flow as it resettles back into the disk.
Key words: galaxies: interactions / galaxies: ISM / galaxies: kinematics and dynamics / galaxies: clusters: individual: Virgo
Appendices are available in electronic form http://www.aanda.org
© ESO, 2012
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