Environmental effects in galaxies

Free access article

Issue		A&A Volume 381, Number 3, January III 2002


Page(s)		771 - 782
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20011566

A&A 381, 771-782 (2002)
DOI: 10.1051/0004-6361:20011566

Molecular gas, star formation, and activity

D. F. de Mello¹, T. Wiklind¹ and M. A. G. Maia²

¹ Onsala Space Observatory, 43992 Onsala, Sweden
e-mail: duilia@oso.chalmers.se, tommy@oso.chalmers.se
² Observatório Nacional, Rua Gal. José Cristino 77, RJ 20921, Brazil
e-mail: maia@on.br

(Received 29 December 2000 / Accepted 15 October 2001 )

Abstract
In order to study whether there is any correlation between nuclear activities, gas content, and the environment where galaxies reside, we have obtained optical and millimetric spectra for a well-defined sample of intermediate Hubble type spirals in dense environments and in the field. We found that these spirals in dense environments have on average: less molecular gas per blue luminosity, a higher atomic gas fraction, lower current star formation rate, and the same star formation efficiency as field galaxies. Although none of these results stands out as a single strong diagnostic given their statistical significance, taken together they indicate a trend for diminished gas content and star-formation activity in galaxies in high-density environments. Our results suggest that galaxies in dense environments have either (i) consumed their molecular gas via star formation in the past or (ii) that dense environments leads to an inhibition of molecular gas from atomic phase. The similarities in star-formation efficiency of the dense environments and field galaxies suggest that the physical processes controling the formation of stars from the molecular gas are local rather than global. We also found that star formation rate per blue luminosity increases linearly as the total amount of gas increases in LINERs. This result, based on a small sample, suggests that LINERs are powered by star formation rather than an AGN.

Key words: galaxies: active -- galaxies: cluster: general -- galaxies: fundamental parameters -- galaxies: Seyfert -- galaxies: spiral

Offprint request: D. de Mello, duilia@oso.chalmers.se

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