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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 Merging Galaxies
In this paper we describe the spectroscopic and infrared properties of asample of 25 merging galaxy pairs, selected from the catalog of Arp& Madore, and we compare them with those observed in a similarsample of interacting galaxies (Donzelli & Pastoriza). It is notedthat mergers as well as interacting systems comprise a wide range ofspectral types, going from those corresponding to well-evolved stellarpopulations (older than 200 Myr) to those that show clear signatures ofH II regions with stellar populations younger than 8 Myr. However,merger galaxies show on average more excited spectra than interactingpairs, which could be attributed to lower gas metallicity. From theemission lines we also found that merging systems show on average higher(about a factor of 2) star formation rates than interacting galaxies.Classical diagnostic diagrams show that only three of 50 of the galaxies(6%) present some form of nuclear activity: two Seyfert galaxies and oneLINER. However, through a detailed analysis of the pure emission-linespectra, we conclude that this fraction may raise up to 23% of themergers if we consider that some galaxies host a low-luminosity activenucleus surrounded by strong star-forming regions. This latterassumption is also supported by the infrared colors of the galaxies.Regarding to the total infrared luminosities, the merging galaxies showon average an IR luminosity, log(Lir)=10.7, lower than thatof interacting systems, log(Lir)=10.9. We find that onlythree mergers of the sample (12%) can be classified as luminous infraredgalaxies, while this fraction increases to 24% in the interactingsample. Based on observations made at CASLEO. ComplejoAstronómico El Leoncito is operated under agreement between theConsejo Nacional de Investigaciones Científicas y Técnicasde la República Argentina and the National Universities of LaPlata, Córdoba and San Juan.
| Candidates for a southern extension of the Karachentsev catalogue of isolated pairs of galaxies.
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