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dc.contributor.advisorRudnick, Gregory H.
dc.contributor.authorDeger, Sinan
dc.date.accessioned2021-02-27T21:03:28Z
dc.date.available2021-02-27T21:03:28Z
dc.date.issued2019-12-31
dc.date.submitted2019
dc.identifier.otherhttp://dissertations.umi.com/ku:16808
dc.identifier.urihttp://hdl.handle.net/1808/31503
dc.description.abstractIn this work, we present our analysis attempting to constrain the prevalence of tidal interaction and merger (TIM) events on the evolution of intermediate redshift galaxies. The main focus of this work is the effect of such events on the star formation properties of galaxies. Such an undertaking requires the precise selection of tidal interactions and mergers (TIMs), in a wide range of environments to account for environmental effects. As such, in the first part of this work we study the fraction of tidal interactions and mergers with well identified observability timescales ($f_{\rm TIM}$) in group, cluster, and accompanying field galaxies and its dependence on redshift ($z$), cluster velocity dispersion ($\sigma$), and environment. We analyze images from the Hubble Space Telescope (HST), and catalogs from the ESO Distant Cluster Survey (EDisCS) for our work. Our data sample consists of 11 clusters, 7 groups, and accompanying field galaxies at $0.4 \leq z \leq 0.8$. We select our TIM sample using both a visual classification of galaxy morphologies and an automated method, the $G-M_{20}$ method. We calibrate this method using the visual classifications that were performed on a subset of our sample. After this calibration, we label visual TIMs also picked by our $G-M_{20}$ selection criterion as \textquotedblleft $G-M_{20}$ TIM \textquotedblright, and gather our visually undisturbed galaxies plus the visual TIMs that are not $G-M_{20}$ selected under the \textquotedblleft undisturbed \textquotedblright label. Our tests indicate that these subpopulations are well-seperated in the $G-M_{20}$ space, and that our results are robust against different $G-M_{20}$ TIM selection criteria. Next, we investigate whether the fraction of $G-M_{20}$ TIMs, or $f_{\rm TIM}$, shows any strong trends with redshift ($z$), cluster velocity dispersion ($\sigma$), and the global environment the in which our galaxies reside. We find marginal evidence for a trend between $f_{\rm TIM}$ and $z$, in that higher $z$ values correspond to higher $f_{\rm TIM}$. However, we also cannot rule out the null hypothesis of no correlation at higher than 68\% confidence. No trend is present between $f_{\rm TIM}$ and $\sigma$. We find that $f_{\rm TIM}$ shows suggestive peaks in groups, and tentatively in clusters at $R > 0.5\times R_{200}$, implying that $f_{\rm TIM}$ gets boosted in these intermediate density environments. However, our analysis of the local densities of our cluster sample does not reveal a trend between $f_{\rm TIM}$ and density, except for a potential enhancement at the very highest densities. We also perform an analysis of projected radius-velocity phase space for our cluster members. Our results reveal that tidal interactions and mergers (TIM), and undisturbed galaxies only have a 6\% probability of having been drawn from the same parent population in their velocity distribution and 37\% in radii, in agreement with the modest differences obtained in $f_{\rm TIM}$ at the clusters. After classifying our sample into $G-M_{20}$ TIMs and undisturbed galaxies, we investigate the stellar populations of our sample. To this purpose, we perform a full spectral fitting on the deep EDisCS spectroscopy data. We use the publicly available pPXF code for the spectral fitting, obtaining the details of the stellar populations, and the gas present in our sample, as results of our spectral fitting. We extract the fraction of the total stellar mass contained in stellar populations of different ages in our sample from this information. We also derive age-sensitive spectral indices, the strength of the narrow 4000$\mbox{\AA}$ break strength, $D_{n,4000}$, and the Balmer H$\mathrm{\delta}$ absorption line index using the results of the spectral fitting. The final part of our analysis attempts to combine our morphological analysis, and our stellar population analysis. We search for trends in our $G-M_{20}$ TIMs and undisturbed galaxies with respect to the ages of their stellar populations. We find that our $G-M_{20}$ TIM galaxies are predominantly star-forming, as derived from multi-band photometric data. A larger fraction of the $G-M_{20}$ TIM galaxies also have features in their galaxy spectra indicating that their light is dominated by young stars. We then analyze the mass-weighted age fractions in the last 0.5 Gyr ($f_{Age 0.5\times R_{200}$, implying that $f_{\rm TIM}$ gets boosted in these intermediate density environments. However, our analysis of the local densities of our cluster sample does not reveal a trend between $f_{\rm TIM}$ and density, except for a potential enhancement at the very highest densities. We also perform an analysis of projected radius-velocity phase space for our cluster members. Our results reveal that tidal interactions and mergers (TIM), and undisturbed galaxies only have a 6\% probability of having been drawn from the same parent population in their velocity distribution and 37\% in radii, in agreement with the modest differences obtained in $f_{\rm TIM}$ at the clusters. After classifying our sample into $G-M_{20}$ TIMs and undisturbed galaxies, we investigate the stellar populations of our sample. To this purpose, we perform a full spectral fitting on the deep EDisCS spectroscopy data. We use the publicly available pPXF code for the spectral fitting, obtaining the details of the stellar populations, and the gas present in our sample, as results of our spectral fitting. We extract the fraction of the total stellar mass contained in stellar populations of different ages in our sample from this information. We also derive age-sensitive spectral indices, the strength of the narrow 4000$\mbox{\AA}$ break strength, $D_{n,4000}$, and the Balmer H$\mathrm{\delta}$ absorption line index using the results of the spectral fitting. The final part of our analysis attempts to combine our morphological analysis, and our stellar population analysis. We search for trends in our $G-M_{20}$ TIMs and undisturbed galaxies with respect to the ages of their stellar populations. We find that our $G-M_{20}$ TIM galaxies are predominantly star-forming, as derived from multi-band photometric data. A larger fraction of the $G-M_{20}$ TIM galaxies also have features in their galaxy spectra indicating that their light is dominated by young stars. We then analyze the mass-weighted age fractions in the last 0.5 Gyr ($f_{Age < 0.5~\mathrm{Gyr}}$), and between 0.5 Gyr and 1 Gyr ($f_{0.5 < Age < 1.0~\mathrm{Gyr}}$). Our results imply an enhanced $f_{Age < 0.5~\mathrm{Gyr}}$ value for the $G-M_{20}$ TIMs. This time interval is comparable in length to merger timescales reported by many studies, thereby this result is indicative of the TIM event boosting the star formation of these galaxies.
dc.format.extent1113 pages
dc.language.isoen
dc.publisherUniversity of Kansas
dc.rightsCopyright held by the author.
dc.subjectPhysics
dc.subjectAstronomy
dc.subjectGalaxy Clusters and Groups
dc.subjectGalaxy Evolution
dc.subjectGalaxy Mergers and Interactions
dc.subjectStar Formation in Galaxies
dc.titleThe Role of Tidal Interactions and Mergers on the Evolution of Intermediate Redshift Galaxies
dc.typeDissertation
dc.contributor.cmtememberBlumenstiel, Justin
dc.contributor.cmtememberCravens, Thomas E.
dc.contributor.cmtememberFeldman, Hume A.
dc.contributor.cmtememberTwarog, Bruce A.
dc.thesis.degreeDisciplinePhysics & Astronomy
dc.thesis.degreeLevelPh.D.
dc.identifier.orcid0000-0003-1943-723X
dc.rights.accessrightsopenAccess


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