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The gas content of peculiar galaxies: Strongly interacting systems
A study of the gas content in 1038 interacting galaxies, essentiallyselected from Arp, Arp & Madore, Vorontsov-Velyaminov catalogues andsome of the published literature, is presented here. The data on theinterstellar medium have been extracted from a number of sources in theliterature and compared with a sample of 1916 normal galaxies. The meanvalues for each of the different ISM tracers (FIR, 21 cm, CO lines,X-ray) have been estimated by means of survival analysis techniques, inorder to take into account the presence of upper limits. From the datait appears that interacting galaxies have a higher gas content thannormal ones. Galaxies classified as ellipticals have both a dust and gascontent one order of magnitude higher than normal. Spirals have in mostpart a normal dust and HI content but an higher molecular gas mass. TheX-ray luminosity also appears higher than that of normal galaxies ofsame morphological type, both including or excluding AGNs. We consideredthe alternative possibilities that the molecular gas excess may derivefrom the existence of tidal torques which produce gas infall from thesurrounding regions or from a different metallicity which affects the Xconversion factor between the observed CO line luminosity and the H_2calculated mass. According to our tests, it appears that interactinggalaxies possess a higher molecular mass than normal galaxies but with asimilar star formation efficiency.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/941
| Spectroscopic Observations of ARP / Madore Interacting Galaxies - Part Two - Galaxies with Tails Loops of Material or Debris
We present spectroscopic observations of 103 galaxies from a sample ofinteracting galaxies with tails, loops of material or debris. Radialvelocities, relative emission-line intensity measurements and opticalclassifications are presented. Three new Seyfert candidates areidentified. The frequency of Seyfert-type nuclei in our sample of`strongly' interacting galaxies (3.9 per cent; 4/103) is notsignificantly different from that of the interacting doubles ofcomparably sized galaxies (3.1 per cent; 4/129), which are presumably atan earlier stage of interaction than the galaxies observed in thepresent-study. However, the lack of a suitable control sample for ourinteracting samples prevents us from confirming whether interactions andmergers enhance Seyfert nuclear activity compared to that of non-interacting galaxies. A large fraction of the galaxies in our sampleshow strong H II region type emission lines, which indicate ongoingenhanced star formation activity. Since the systems are at a relativelyearly stage of the merger process and are near the peak of theirstarburst activities, the interstellar gas in the disc must be collectedin the nuclear region on time-scales less than about a few X 10^8^-10^9^yr. Strong H II region type emission lines superimposed on a strongstellar Balmer absorption spectrum are seen in many of the systems inour sample, suggesting a possible recurrent starburst or propagation ofstar-forming regions within the galaxy. High-resolution imaging studiesare required for further analysis of the sample.
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