The gas content of peculiar galaxies: Strongly interacting systems^*

¹ Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy e-mail: [galletta; casasola]@pd.astro.it
² Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy e-mail: bettoni@pd.astro.it

Received: 17 February 2004
Accepted: 28 April 2004

Abstract

A study of the gas content in 1038 interacting galaxies, essentially selected from Arp, Arp & Madore, Vorontsov-Velyaminov catalogues and some of the published literature, is presented here. The data on the interstellar medium have been extracted from a number of sources in the literature and compared with a sample of 1916 normal galaxies. The mean values for each of the different ISM tracers (FIR, 21 cm, CO lines, X-ray) have been estimated by means of survival analysis techniques, in order to take into account the presence of upper limits. From the data it appears that interacting galaxies have a higher gas content than normal ones. Galaxies classified as ellipticals have both a dust and gas content one order of magnitude higher than normal. Spirals have in most part a normal dust and HI content but an higher molecular gas mass. The X-ray luminosity also appears higher than that of normal galaxies of same morphological type, both including or excluding AGNs. We considered the alternative possibilities that the molecular gas excess may derive from the existence of tidal torques which produce gas infall from the surrounding regions or from a different metallicity which affects the X conversion factor between the observed CO line luminosity and the H₂ calculated mass. According to our tests, it appears that interacting galaxies possess a higher molecular mass than normal galaxies but with a similar star formation efficiency.