The Star-Forming Properties of Violently Interacting Galaxies
Bushouse, Howard Alan
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https://hdl.handle.net/2142/70667
Description
Title
The Star-Forming Properties of Violently Interacting Galaxies
Author(s)
Bushouse, Howard Alan
Issue Date
1986
Department of Study
Astronomy
Discipline
Astronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Astronomy and Astrophysics
Abstract
The effects of galaxy-galaxy collisions on star formation are investigated for a large, morphologically selected sample of strongly interacting disk-type galaxies. Current star formation rates, stellar contents, and spatial distributions of star forming sites are explored on both global and nuclear scales via narrow-band imaging and spectrophotometry.
Measurements of total H(alpha) fluxes reveal an average increase in global star formation rates of about a factor of 2.5 over isolated spiral galaxies. Alternatively, an analysis of far-infrared luminosities shows that the interacting galaxies have anomalously high L(IR)/L(H(alpha)) ratios, and this leads to L(IR)-derived global star formation rates that, on average, are a factor of 6 higher than in isolated spiral galaxies. Quantitative analyses of the spatial distribution of star forming sites suggests that the majority of enhanced star formation activity is concentrated near the nuclei of the interacting galaxies. No correlation is found between global star formation rates and either HI gas content or optical luminosity.
The nuclei of the interacting galaxies exhibit a wide range in star formation rates, but have significantly higher overall levels of both H(alpha) emission-line equivalent width and luminosity than samples of isolated spiral galaxies. However, a surprisingly large fraction ((TURN)30%) of the nuclei are characterized by stellar absorption spectra reminiscent of old, elliptical galaxy-like stellar populations.
The implications of this work are four-fold. First, the disk regions of galaxies are not strongly affected (in terms of star formation) as a result of an interaction with a close companion. Second, when interaction-induced activity does occur, it is primarily seen as an enhancement in the star formation rate in and around the nuclear regions of a galaxy. Third, exotic forms of nuclear activity, such as Seyferts, are not optically detectable in this sample of interacting galaxies. Fourth, while the observations agree in general with theoretical models, no explanations exist for (1) those galaxies that have not experienced any significant levels of star formation activity for a length of time comparable to the dynamical timescale for interactions, and (2) the overall lack of Seyfert and LINER nuclei in the sample.
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