Gas flows in interacting galaxies: a multiwavelength study




Scudder, Jillian Marie

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A galaxy’s evolution is quite sensitive to the impact of external influences. In this thesis, the impact of external environment from both large and small scale effects is investigated, along with a study of how the HI gas fraction of a galaxy can modulate a galaxy’s response to perturbations by galaxy–galaxy interactions. This thesis makes use of the statistical power of the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) to assemble a large spectroscopic sample of galaxies, select samples of interest, and select control samples of galaxies matched to each galaxy within the sample of interest in mass, redshift, and (if applicable) local density. It is possible to trace a galaxy’s internal gas motions which mark its disturbance by using the metrics of star formation rate (SFR) and gas-phase metallicity. To investigate the influence of large scale environment, a sample of star forming galaxies in a locally dense environment, but relatively isolated from larger scale structure, is constructed. This sample is further divided into groups which are truly isolated from any large scale structure (no cluster potential within 1 Mpc), and those which, in spite of their relative local isolation, are embedded within a larger cluster structure (within 1 Mpc of a cluster). As the local galaxy density is identical between isolated and embedded group structures, a fair comparison between the star forming properties of the galaxies within those group structures can be made. Star forming galaxies whose groups are embedded within a larger structure are found to show statistically lower SFRs than those galaxies whose groups are truly isolated from any larger cluster potential. The impact of local galaxy–galaxy interactions is subsequently considered. Using a sample of star-forming galaxies in pairs from the SDSS DR7, the enhancement in SFRs and the suppression of metallicities is traced as a function of projected separation (rp). The metallicity dilution as a function of rp is presented for the first time. Galaxies in pairs are found to have SFRs and metallicity values which are offset from a carefully selected control sample to separations of at least 80 kpc/h. Using a suite of simulations developed for the purposes of comparison with these observational results, a new interpretive framework is developed for enhancements as a function of rp. To investigate the role that gas fraction plays in moderating the strength of interaction triggered starbursts, new data is obtained from the Jansky Very Large Array (VLA). The VLA data supplements the existing SDSS data with HI gas masses for a subsample of resolvable galaxy pairs at small rp(in kpc/h). HI masses are obtained and gas fractions are calculated for a sample of 34 paired galaxies. A positive correlation is detected at > 2σ between the gas fraction of a galaxy and the SFR enhancement of that galaxy. The work presented in this thesis has expanded the understanding of physical variables, both internal and external, which can change the star forming properties of a galaxy through an examination of tracers of internal gas flows in those galaxies.



Astrophysics, Galaxy interactions, Galaxy environments, Extragalactic astronomy, Radio astronomy