We present new proper motion (PM) measurements of the dwarf spheroidal galaxies (dSphs) Draco and Sculptor using multiepoch images obtained with the Hubble Space Telescope ACS/WFC. Our PM results have uncertainties far lower than previous measurements, even those made with the same instrument. The PM results for Draco and Sculptor are (mu(W),mu(N))(Dra) = (-0.0562 +/- 0.0099, -0.1765 +/- 0.0100 mas yr(-1) and (mu(W), mu(N) )(Scl) = (-0.0296 +/- 0.0209, 0.1358 +/- 0.0214 mas yr(-1)) -1. The implied Galactocentric velocity vectors for Draco and Sculptor have radial and tangential components: (V-rad, V-tan)(Dra) =(-88.6, 161.4) +/- (4.4, 5.6) km s(-1) and (V-rad, V-tan )(Scl) = (72.6, 200.2)+/-(1.3, 10.8) km s(-1). We study the detailed orbital histories of both Draco and Sculptor via numerical orbit integrations. Orbital periods of Draco and Sculptor are found to be 1-2 Gyr and 2-5 Gyr, respectively, accounting for uncertainties in the Milky Way (MW) mass. We also study the influence of the Large Magellanic Cloud (LMC) on the orbits of Draco and Sculptor. Overall, the inclusion of the LMC increases the scatter in the orbital results. Based on our calculations, Draco shows a rather wide range of orbital parameters depending on the MW mass and inclusion/exclusion of the LMC, but Sculptor's orbit is very well constrained, with its most recent pericentric approach to the MW being 0.3-0.4 Gyr ago. Our new PMs imply that the orbital trajectories of both Draco and Sculptor are confined within the " Disk of Satellites," better so than implied by earlier PM measurements, and likely rule out the possibility that these two galaxies were accreted together as part of a tightly bound group.

We present HST Goddard High Resolution Spectrograph and Space Telescope Imaging Spectrograph observations of five quasi stellar objects that probe the prominent high-velocity cloud (HVC) Complex C, covering ∼10% of the northern sky. Based upon a single sight-line measurement (Mrk 290), a metallicity [S/H] = -1.05 ± 0.12 has been associated with Complex C by Wakker et al. When coupled with its inferred distance (5 ≲ d ≲ 30 kpc) and line-of-sight velocity (v ∼ -100 to -200 km s-1), Complex C appeared to represent the first direct evidence for infalling low-metallicity gas onto the Milky Way, which could provide the bulk of the fuel for star formation in the Galaxy. We have extended the abundance analysis of Complex C to encompass five sight lines. We detect S n absorption in three targets (Mrk 290, 817, and 279); the resulting [S II/H I] values range from -0.36 (Mrk 279) to -0.48 (Mrk 817) to -1.10 (Mrk 290). Our preliminary O I FUSE analysis of the Mrk 817 sight line also supports the conclusion that metallicities as high as 0.3 times solar are encountered within Complex C. These results complicate an interpretation of Complex C as infalling low-metallicity Galactic fuel. Ionization corrections for H II and S III cannot easily reconcile the higher apparent metallicities along the Mrk 817 and Mrk 279 sight lines with that seen toward Mrk 290, since Hα emission measures preclude the existence of sufficient H II. If gas along the other lines of sight has a similar pressure and temperature to that sampled toward Mrk 290, the predicted Hα emission measures would be ∼900 mR. It may be necessary to reclassify Complex C as mildly enriched Galactic waste from the Milky Way or processed gas torn from a disrupted neighboring dwarf, as opposed to low-metallicity Galactic fuel.

Using the redMaPPer catalog of 21709 galaxy clusters and photometric information for 455946 galaxies from SDSS DR8, we study the effects of local and global environment on galaxy evolution within clusters in the redshift range 0.2 ≤ z ≤ 0.5 and the richness range 20 ≤ λ ≤ 236. We use cluster richness λ as a proxy for global environment and cluster-centric radius dBCG to represent the local environ- ment within clusters. We measure giant-to-dwarf ratio (GDR) which gives insight regarding the composition of the red sequence, and we measure red fraction which holds information about the rate at which galaxies falling into clusters cease to form new stars and build up the red sequence in a phenomenon called quenching. We ob- serve that red fraction decreases with redshift, increases with λ, and decreases with dBCG. GDR, meanwhile, decreases with redshift, does not vary significantly with λ, and decreases with dBCG. All together, our results tell the story of clusters starting with bright, massive galaxies which accrete smaller and smaller galaxies over time. The galaxies are quickly quenched upon entering clusters environment. We observe that most quenching occurs on smaller richness scales than our data covers, and that by the time clusters have grown to the richnesses redMaPPer is sensitive to, ram pressure stripping is likely to be the dominant quenching mechanism. / Graduate

abstract: Learning how properties of galaxies such as star formation, galaxy interactions, chemical composition, and others evolve to produce the modern universe has long been a goal of extragalactic astronomy. In recent years, grism spectroscopy from the Hubble Space Telescope (HST) has provided a means to study these properties with spectroscopy while avoiding the limitations of ground-based observation. In this dissertation, I present several studies wherein I used HST G102 grism spectroscopy from the Faint Infrared Grism Survey (FIGS) to investigate these fundamental properties of galaxies and how they interact and evolve. In the first study, I combined the grism spectra with broadband photometry to produce a catalog of redshifts with improved accuracy, reducing the median redshift error from 3\% to 2\%. With this redshift catalog, I conducted a systematic search for galaxy overdensities in the FIGS fields, producing a list of 24 significant candidates. In the second study, I developed a method for identifying emission line galaxy (ELG) candidates from continuum-subtracted 1D spectra, and identified 71 ELGs in one FIGS field. In matching MUSE/VLT spectra, I measured the [OIII]$\lambda$4363 emission line for 14 FIGS ELGs, and used this to measure their $T_e$-based gas-phase metallicities. These ELGs show a low-metallicity offset on the Mass-Metallicity Relation, and I demonstrated that this offset can be explained by recent star formation. In the third study, I expanded the ELG search to all four FIGS fields, identifying 208 H$\alpha$, [OIII]$\lambda\lambda$4959,5007, and [OII]$\lambda\lambda$3727,3729 line emitters. I compiled a catalog of line fluxes, redshifts, and equivalent widths. I combined this catalog with the overdensity study to investigate a possible relationship between line luminosity, star formation, and an ELG's environment. In the fourth study, I usde 15 FIGS H$\alpha$ emitters and 49 ``green pea'' line emitters to compare H$\alpha$ and the far-UV continuum as tracers of star formation. I explored a correlation between the H$\alpha$-FUV ratio and the ratio of [OIII]$\lambda\lambda$4959,5007 to [OII]$\lambda\lambda$3727,3729 and its implications for star formation history. / Dissertation/Thesis / Doctoral Dissertation Astrophysics 2019

I present Hubble Space Telescope photometry in optical (F475X, 475 nm) and near-infrared (F110W, 1.1 μm) bands of the globular cluster (GC) system of the inner haloes of a sample of 15 brightest cluster galaxies (BCGs). I also present a quantitative model of the relation between (F475X - F110W) colour and cluster metallicity, using simulated GCs. The sample comprises massive elliptical galaxies in a range of environments, from sparsely populated groups to dense clusters. Because the material available for large galaxies to accrete varies with environment and GC systems of such galaxies are built up through accretion, I expect the metallicity distribution of the GC systems in my sample to vary with galaxy environment. GC systems in massive elliptical galaxies tend to follow a bimodal colour distribution, with two subpopulations of blue (metal-poor) and red (metal-rich) clusters. The photometry is used to create a completeness-corrected metallicity histogram for each galaxy in my sample, and to fit a double Gaussian curve to each histogram in order to model the two subpopulations. Finally, the properties of the GC metallicity distribution are correlated against each BCG environment. I found that almost no GCS properties and host galaxy environmental properties are correlated, with the exception of weak but consistent correlations between number of GCs and nth-nearest neighbour surface density and between blue fraction and nth-nearest neighbour surface density. / Thesis / Master of Science (MSc)

No description available.

<p>The influence of environment in galaxy evolution has been observed in a wide range of environments, where in general red quiescent early-type galaxies preferentially reside in high-density regions. The aim of this thesis is to understand the role that galaxy groups, and in particular group dynamics, play in galaxy evolution.</p> <p>We examine substructure in rich groups at intermediate redshifts and find that 4/15 groups contain substructure, which is preferentially found on the group outskirts. Galaxies in groups with substructure have properties similar to the field, while the galaxies in groups with no substructure are similar to cluster populations. These results indicate that substructure galaxies do not feel the effects of the environment until well inside the group potential.</p> <p>We then study the evolution of group dynamics to z~1 and find that the fraction of non-Gaussian groups increases with redshift, while the fraction of groups with substructure remains constant. Additionally, we find that the quiescent fraction correlates with galaxy stellar mass, but has little or no dependence on group dynamical mass or state. However, we do observe some correlation between substructure and quiescent fraction for low mass galaxies.</p> <p>Finally, we investigate infalling subhalo galaxies to probe the importance of pre-processing in galaxy evolution. At r200 > 2, galaxies in subhaloes show enhanced quenching, when compared to non-subhalo galaxies. At these radii, the infall population dominates, indicating that enhanced quenching is due to the infalling subhalo population. Additionally, the fraction of groups with subhaloes is a function of halo mass, where more massive systems have a higher fraction of subhaloes. We conclude that for groups, pre-processing is insignificant; however, for the most massive clusters a significant fraction (∼ 25%) of the member galaxies have been pre-processed.</p> / Doctor of Philosophy (PhD)

No description available.

We study the influence of environment on galaxy evolution by focusing on two galaxy types known for their connection to dense environments, S0s and Brightest Cluster Galaxies (BCGs). Our goal is to identify the mechanisms responsible for the properties of galaxies in groups and clusters. We first examine the effects of environment on S0 formation over the past ~7 Gyr by tracing the increasing S0 fraction in clusters at two mass scales. We find the build-up of S0s driven by groups/clusters with velocity dispersions σ ≲ 750 km s⁻¹, suggesting mechanisms that operate most efficiently via slow encounters (e.g., mergers and tidal interactions) form S0s.With less-massive halos identified as the site for S0 formation, we test whether another route to S0 formation exists, not in isolated groups but rather in a system of four merging groups (SG1120). We place limits on how recent the S0s in that system could have formed, and finding no star formation, conclude they formed ≳ 1 Gyr prior to SG1120's current configuration, when they were in more isolated groups. We next explore cluster outskirts to constrain the number of infalling galaxies that need to be transformed and whether that process has already begun. We find the red fraction of infalling galaxies is elevated relative to the field, and that red galaxies are more clustered than blue ones, a signature of "pre-processing". We disentangle the relative strength of global versus local environment on galaxy transformation by comparing the correlation of red fraction with radius and local density. We find that both parameters are connected with the red fraction of galaxies. Finally, we measure the frequency of galaxies falling into the cluster that are bright enough to supplant the current BCG and compare the results to models. We find in ~ 85% of our clusters that the BCG is secure and remains in its priviledged state until z ~ 0.From these analyses, we find that intermediate density environments (groups and cluster outskirts) are the key site to forming S0 galaxies, and that BCGs, while not exclusively a cluster phenomenon, are well established by the redshifts we explore.

No description available.