Mathematics – Probability
Scientific paper
Apr 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt........13a&link_type=abstract
Ph.D. thesis, Univ. Potsdam, (1998)
Mathematics
Probability
3
Galaxies: Clusters Of, Infrared: Galaxies
Scientific paper
Interacting galaxies are ideal laboratories for studying the influence of gravitational forces on galaxies. From theoretical and observational studies, we know how sensitive galaxies are to tidal interaction, from the formation of tidal tails, bridges, bursts of star formation up to a complete merging of the galaxies. The Far Infrared (FIR) properties of interacting galaxies give information on the dynamical and physical properties of these systems. Several earlier studies using the IRAS point source catalogue (IPSC) and IRAS Faint Source Survey (FSS), showed that the FIR emission from interacting/merging galaxies is enhanced with respect to isolated non-interacting galaxies; moreover, that high density environments have more influence in producing enhanced FIR emission over isolated interacting systems. In general the ratio of FIR to optical luminosity in interacting systems was found to be enhanced. It is regarded as an increased star formation (SF) rate in these systems. Later on, due to the rather high IPSC detection threshold, and its low resolution, several contradictory results have been reported. In this thesis the FIR emission from interacting galaxies is studied by using the high resolution IRAS software introduced by Bontekoe et al. (1994). This soft ware package uses a Maximum Entropy method (hereafter MaxEnt). The MaxEnt formulation is rooted in Bayesian probability theory. The raw IRAS data contains the Point Spread Function (PSF) of both the telescope mirror (60 cm --> 1 arcmin at 60 μm) and the PSF of the detectors (≃ 5 arcmin). Since there is much redundancy in the data, the MaxEnt routine can be used to remove the 5 arcmin PSF from the detectors. For many interacting galaxies this is enough to resolve them. The size of the images was chosen such that the objects could be studied including their surroundings. The absolute position calibration and flux estimates for the MaxEnt images are described in Allam et al. (1996). Because of the high resolution of the MaxEnt images, a much more detailed investigation, compared to previous studies using the IPSC and FSS, of the effects of galaxy-galaxy interaction on triggerin g starbursts could be carried out. MaxEnt images have been produced for isolated galaxies, galaxy pairs, and compact groups of galaxies. The isolated galaxies are used to define reference FIR properties to which those of the other samples have been compared. The MaxEnt images have been compared with optical images from the Digitized SkySurvey. This comparison showed that previous studies ascribed too much, or too little, FIR energy to individual galaxies. Secondly, the FIR and Blue luminosities have been compared in order to estimate the star formation rates in the studied samples. The FIR fluxes have finally been used to estimate dust temperatures and masses of the objects. Many of the interacting systems in the sample show optical signs of interaction such as tidal tails and bridges. Fuelling processes during interaction are found in some of the gas rich systems. However, the FIR emission of some of the pairs and groups are similar to that of the isolated galaxies. The major - and unexpected - result from this dissertation research is that for the pairs and groups of galaxies the FIR to optical luminosity ratio is not enhanced with respect to isolated galaxies. This means that there is no enhancement in star formation rates. Also, all galaxies studied (isolated, pairs, and groups) have undistinguishable color temperatures. The only exception are systems that are clearly merging and Seyfert 2 galaxies. These objects do have an increased FIR to optical luminosity ratio and temperature. Some of the pairs and groups seem to have FIR envelopes surrounding all members; in some cases the FIR envelope is even bigger than that at radio wavelengths. No clear correlation can be found between the presence of structure in ellipticals (e.g. shells) in the samples and the presence of diffuse FIR emission. Also the sense of an encounter (direct vs. retrograde) has no effect on the FIR emission.
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