Resolved properties of galaxy mergers from the MaNGA survey

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dc.contributor.author Thorp, Mallory D.
dc.date.accessioned 2019-08-23T18:22:49Z
dc.date.available 2019-08-23T18:22:49Z
dc.date.copyright 2019 en_US
dc.date.issued 2019-08-23
dc.identifier.uri http://hdl.handle.net/1828/11062
dc.description.abstract The complex and diverse populations of galaxies observed today form hierarchically through past galactic mergers. Interactions between galaxies of similar masses will drastically alter the morphology, chemical composition, star-formation activity, and central black-hole accretion of their constituents. Though we can see the components and byproducts of galaxy mergers, these events endure over a timescale of hundreds of millions of years. Thus to understand the merging process from observations, astronomers are reliant on large spectroscopic surveys which will contain galaxy mergers at various stages of interaction, and those which have just experienced coalescence. Until recently, such surveys were limited to the global properties of each galaxy, constraining the global changes in chemical composition and star-formation activity, but overlooking how such changes vary across a galaxy. The advent of Integral Field Unit (IFU) spectroscopy surveys provides spatially resolved spectroscopic properties for thousands of galaxies for the first time. This thesis presents analysis of galaxy mergers from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) IFU spectroscopy survey. Enhancements and deficits in star-formation rate and metallicity, as a result of the interaction, are determined for each spatial pixel containing a spectrum (spaxel) based on well established relationships with stellar mass density. These offsets are then compressed into radial profiles to quantify how the effects of an interaction vary as a function of radius. A sample of 36 post-mergers are, on average, enhanced out to ~2 effective radii, though individual galaxies can be enhanced or suppressed in the outskirts depending on the global star-formation rate of the galaxy. The metallicity is uniformly suppressed in post-merger galaxies, in concordance with the global SFR enhancement. A sample of galaxy pairs is identified with cuts in the projected separation, the line of sight velocity difference, and the mass ratio of the interaction. I develop a method to deblend close galaxy pairs that are on the same IFU observation, and remove contribution from the companion galaxy in the radial profile. Radial profiles of SFR and metallicity offsets for the pairs sample, binned by projected separation, confirm that central enhancements in SFR increase as separation decreases. Behaviour in the outskirts is more varied, and does not appear to correlate with the projected separation or the mass ratio of the interaction. Metallicity offsets display a similar issue, showing no clear correlation with separation or mass ratio. Such ambiguity implies that multiple characteristics of the interaction and its components are required to predict the spatial changes in a galaxy merger. I propose projects that could shed light on these ambiguities. The most recent release of MaNGA will double the sample size of mergers, possibly homogenizing projected separation and mass ratio bins that may be dominated by a particular population. An analysis of interacting galaxies that do not have mass ratio measurements, but very small projected separations and highly disturbed morphologies, could provide understanding of the transition between the very end of an interaction and the state of the galaxy post-coalescence. I also propose a more complex analysis of the asymmetry of IFU spectroscopy data products, which until now have been simplified with radial profiles. Lastly, I emphasize the importance of follow up studies of the resolved molecular gas properties of merging galaxies to discern whether gas reservoir, depletion time, or both are driving the change in star-formation rate. en_US
dc.language English eng
dc.language.iso en en_US
dc.rights Available to the World Wide Web en_US
dc.subject galaxies en_US
dc.subject galaxy mergers en_US
dc.subject integral field spectroscopy en_US
dc.subject IFS en_US
dc.subject Mapping Nearby Galaxies at Apache Point Observatory en_US
dc.subject MaNGA en_US
dc.subject astronomy en_US
dc.title Resolved properties of galaxy mergers from the MaNGA survey en_US
dc.type Thesis en_US
dc.contributor.supervisor Ellison, Sara L.
dc.degree.department Department of Physics and Astronomy en_US
dc.degree.level Master of Science M.Sc. en_US
dc.description.scholarlevel Graduate en_US

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