We present a multi-epoch Hubble Space Telescope (HST) study of stellar proper motions (PMs) for four fields along the Orphan Stream. We determine absolute PMs of several individual stars per target field using established techniques that utilize distant background galaxies to define a stationary reference frame. Five Orphan Stream stars are identified in one of the four fields based on combined color-magnitude and PM information. The average PM is consistent with the existing model of the Orphan Stream by Newberg et al. In addition to the Orphan Stream stars, we detect stars that likely belong to other stellar streams. To identify which stellar streams these stars belong to, we examine the 2d bulk motion of each group of stars on the sky by subtracting the PM contribution of the solar motion (which is a function of position on the sky and distance) from the observed PMs, and comparing the vector of net motion with the spatial extent of known stellar streams. By doing this, we identify candidate stars in the Sagittarius and Lethe streams, and a newly found stellar stream at a distance of similar to 17 kpc, which we tentatively name the "Parallel Stream." Together with our Sagittarius stream study, this work demonstrates that even in the Gaia era, HST will continue to be advantageous in measuring PMs of old stellar populations on a star-by-star basis, especially for distances beyond similar to 10 kpc.

The observable properties of galaxy groups, and especially the thermal and chemical properties of the intragroup medium (IGrM), provide important constraints on the different feedback processes associated with massive galaxy formation and evolution. In this {work}, we present a detailed analysis of the global properties of simulated galaxy groups with X-ray temperatures in the range $0.5 - 2$ keV over the redshift range $0 \leq z \leq 3$. The groups are drawn from a cosmological smoothed particle hydrodynamics simulation that includes a well-constrained prescription for momentum-driven, galactic outflows powered by stars and supernovae but no explicit treatment of AGN feedback. Our aims are (a) to establish a baseline against which we will compare future models; (b) to identify model successes that are genuinely due to stellar/supernovae-powered outflows; and (c) to pinpoint mismatches that not only signal the need for AGN feedback but also constrain the nature of this feedback. We find that even without AGN feedback, our simulation successfully reproduces the observed present-day group properties such as the IGrM mass fraction, the various X-ray luminosity-temperature-entropy scaling relations, as well as both the mass-weighted and the emission-weighted IGrM iron and silicon abundance versus IGrM temperature relationships, for all but the most massive groups. We also show that these trends evolve self-similarly for $z < 1$, in agreement with the observations. In contrast to the usual expectations, we do not see any evidence of the IGrM undergoing catastrophic cooling. And yet, the $z=0$ group stellar mass is a factor of $\sim 2$ too high. Probing further, we find that the latter is due to the build-up of cold gas in the massive galaxies {\it before} they are incorporated inside groups. This not only indicates that another feedback mechanism must activate as soon as the galaxies achieve $M_*\approx$ a few $\times 10^{10}\;\rm{M_{\odot}}$ but that this feedback mechanism must be powerful enough to expel a significant fraction of the halo gas component from the galactic halos. ``Maintenance-mode" AGN feedback of the kind observed in galaxy clusters will not do. At the same time, we find that stellar/supernovae-powered winds are essential for understanding the metal abundances in the IGrM and these results are expected to be relatively insensitive to the addition of AGN feedback. We further examine the detailed distribution of the metals within the groups and their origin. We find that our simulated abundance profiles fit the observational data pretty well except that in the innermost regions, there appears to have an excess of metals in the IGrM, which is attributed to the overproduction of stars in the central galaxies. The fractional contribution of the different types of galaxies varies with radial distances from the group center. While the enrichment in the core regions of the groups is dominated by the central and satellite galaxies, the external galaxies become more important contributors to the metals at $r\simgreat R_{500}$. The IGrM at the groups' outskirts is enriched at comparatively higher redshifts, and by relatively less massive galaxies. / Graduate

In this thesis I investigate the hosts and cluster environments of a sample of 41 radio galaxies between z = 0.4 and z = 0.6. I use spectroscopic data for a 24 object subsample to investigate their star formation histories via the strength of the 4000A break. I find that the higher radio luminosity or high excitation objects in the sample have evidence for young stellar populations, but the lower radio luminosity or low excitation objects do not. My investigations into the Fundamental Plane (FP) of 18 of the radio galaxies, using the same spectroscopic data as well as data from the literature, show that the Fanaroff- Riley type I objects (FRIs) lie on the FP of local radio galaxies once corrected for passive evolution but the Fanaroff-Riley type II objects (FRIIs) do not. I suggest that an evolution in the size of the host galaxies, aided by a combination of passive evolution and a mass-dependent evolution in the mass-to-light ratios, may explain the observed offsets. Finally, I use wide field multi-band imaging to investigate the cluster environments of the full z ~ 0.5 sample. I find that the environmental overdensity is positively correlated with the radio luminosity and observe a greater number of close companions around the FRIIs than the FRIs (albeit with only nine FRIs in the sample). The cluster environments of the radio galaxies with the greatest host luminosities show tentative evidence for an alignment between the major axis of a galaxy and that of its cluster, whilst there are hints that the objects with the highest radio luminosities have clusters whose major axis is aligned with the position angle of the radio jet. My results suggest a picture in which FRII type radio sources reside in particularly rich cluster environments at z ~ 0.5 but FRI type radio sources in less rich environments. The environment plays a key role in determining both the radio properties of the galaxy and the evolution of its host. The effect of the environment on the emission line properties and star formation histories of the galaxies leads to the overlap seen in the morphological and spectral properties of radio galaxies.

We use Bayesian statistics and Markov chain Monte Carlo (MCMC) techniques to construct dynamical models for the spiral galaxy NGC 6503. The constraints include surface brightness profiles which display a Freeman Type II structure; HI and ionized gas rotation curves; the stellar rotation, which is nearly coincident with the ionized gas curve; and the line of sight stellar dispersion, which displays a $\sigma-$drop at the centre. The galaxy models consist of a S\'rsic bulge, an exponential disc with an optional inner truncation and a cosmologically motivated dark halo. The Bayesian/MCMC technique yields the joint posterior probability distribution function for the input parameters, allowing constraints on model parameters such as the halo cusp strength, structural parameters for the disc and bulge, and mass-to-light ratios. We examine several interpretations of the data: the Type II surface brightness profile may be due to dust extinction, to an inner truncated disc or to a ring of bright stars; and we test separate fits to the gas and stellar rotation curves to determine if the gas traces the gravitational potential. We test each of these scenarios for bar stability, ruling out dust extinction. We also find that the gas cannot trace the gravitational potential, as the asymmetric drift is then too large to reproduce the stellar rotation. The disc is well fit by an inner-truncated profile, but the possibility of ring formation by a bar to reproduce the Type II profile is also a realistic model. We further find that the halo must have a cuspy profile with $\gamma \gtrsim 1$; the bulge has a lower $M/L$ than the disc, suggesting a star forming component in the centre of the galaxy; and the bulge, as expected for this late type galaxy, has a low S\'{e}rsic index with $n_b\sim1-2$, suggesting a formation history dominated by secular evolution. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2010-01-10 00:11:41.946

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. / Graduate / 0606 / jillian.scudder@gmail.com

We perform spectral energy distribution fitting to the total integrated light, bulge and disk components of ≈ 650,000 spectroscopically selected galaxies from the sloan digital sky survey data release 7. Using 4-band photometry (u, g, r, i) we derive physical properties for these components with particular emphasis placed on the star formation rates (SFR) and stellar masses. Using the total integrated fits as an indicator of the goodness of fit, we show that reliable estimates of the SFR can be recovered using a specific SFR (sSFR) cut of log(sSFR /yr) ≥ −10.45. We construct a close pairs sample and match isolated controls based on stellar mass, z and local density for galaxies that pass the sSFR cut. We develop a method to cross correlate the pair galaxies’ star formation rate posterior probability distribution functions (SFR PDFs) with the control SFR PDFs as a function of the pair galaxies projected separation, rp. We show that the SFR of the close pair galaxies is enhanced relative to the control sample. The SFR enhancement is at a level of ≈ 0.25 dex above that of the control at the closest separations and declines to a plateau at ≈ 0.15 dex for separations of 30 < rp < 60 kpc/h. Between 60 < rp < 80 kpc/h there appears to be a slight increase in the enhancement to a level ≈ 0.25 dex above the control. It is suggested that we observe this increase, where other studies have failed to, based on the updated photometry provided by Simard et al. (2011). From our total pair sample we also select a subsample of galaxies that are classified as active galactic nuclei (AGN). We note that at close separations the pair AGN galaxies have enhanced SFRs relative to their matched controls. The SFR enhancement is largest at the smallest separations, reaching a level of ≈ 0.3 dex above the control. The SFR enhancement for the AGN pairs becomes consistent with their controls at projected separations of 20 < rp < 80 kpc/h. We construct a bulge and disk pair sample that are required to pass the sSFR cut and match control bulges and disks, respectively, that also pass the sSFR cut. We cross correlate the bulge and disk pairs with their respective controls. We measure significant SFR enhancement in the bulge component of the interacting pairs. The SFR enhancement is highest at small separations, ≈ 0.4 dex, and steadily declines to ≈ 0.1 dex before turning around beyond rp > 50 kpc/h to again reach a level ≈ 0.4 dex above the control bulges. The disk SFR enhancement is relatively flat beyond rp > 30 kpc/h to a level ≈ 0.1 dex above the control and largely consistent with the control at close separations. The bulge and disk results suggest that the majority of induced star formation during an interaction is occurring in the bulge component, but that there is still slight SFR enhancement in the disk. We suggest that the upturn in the total and bulge SFR enhancement could potentially be caused by a delay between the interaction of the galaxy pairs and the onset of induced star formation. / Graduate

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. / Graduate / 0606 / jillian.scudder@gmail.com

abstract: New measurements of the Hα luminosity function (LF) and star formation rate (SFR) volume density are presented for galaxies at z∼0.62 in the COSMOS field. These results are part of the Deep And Wide Narrowband Survey (DAWN), a unique infrared imaging program with large areal coverage (∼1.1 deg 2 over 5 fields) and sensitivity (9.9 × 10 −18 erg/cm 2 /s at 5σ). The present sample, based on a single DAWN field, contains 116 Hα emission- line candidates at z∼0.62, 25% of which have spectroscopic confirmations. These candidates have been selected through comparison of narrow and broad-band images in the infrared and through matching with existing catalogs in the COSMOS field. The dust-corrected LF is well described by a Schechter function with L* = 10 42.64±0.92 erg s −1 , Φ* = 10 −3.32±0.93 Mpc −3 (L* Φ* = 10 39.40±0.15 ), and α = −1.75 ± 0.09. From this LF, a SFR density of ρ SF R =10 −1.37±0.08 M○ yr −1 Mpc −3 was calculated. An additional cosmic variance uncertainty of ∼ 20% is also expected. Both the faint end slope and luminosity density that are derived are consistent with prior results at similar redshifts, with reduced uncertainties. An analysis of these Hα emitters’ sizes is also presented, showing a direct corre- lation between the galaxies’ sizes and their Hα emission. / Dissertation/Thesis / Masters Thesis Astrophysics 2017

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides spectroscopic information of regions of the inner Milky Way, which are inaccessible to optical surveys. We present the first large study of the metallicity distribution of the innermost Galactic regions based on high-quality measurements for 7545 red giant stars within 4.5 kpc of the Galactic center, with the goal to shed light on the structure and origin of the Galactic bulge. Stellar metallicities are found, through multiple Gaussian decompositions, to be distributed in several components, which is indicative of the presence of various stellar populations such as the bar or the thin and the thick disks. Super-solar ([Fe/H] = +0.32) and solar ([Fe/H] = +0.00) metallicity components, tentatively associated with the thin disk and the Galactic bar, respectively, seem to be major contributors near the midplane. A solar-metallicity component extends outwards in the midplane but is not observed in the innermost regions. The central regions (within 3 kpc of the Galactic center) reveal, on the other hand, the presence of a significant metal-poor population ([Fe/H] = -0.46), tentatively associated with the thick disk, which becomes the dominant component far from the midplane (vertical bar Z vertical bar >= +0.75 kpc). Varying contributions from these different components produce a transition region at +0.5 kpc <= vertical bar Z vertical bar <= +1.0 kpc, characterized by a significant vertical metallicity gradient.

APOGEE-2 is a high-resolution, near-infrared spectroscopic survey observing similar to 3. x. 10(5) stars across the entire sky. It is the successor to APOGEE and is part of the Sloan Digital Sky Survey IV (SDSS-IV). APOGEE-2 is expanding on APOGEE's goals of addressing critical questions of stellar astrophysics, stellar populations, and Galactic chemodynamical evolution using (1) an enhanced set of target types and (2) a second spectrograph at Las Campanas Observatory in Chile. APOGEE-2 is targeting red giant branch and red clump stars, RR Lyrae, lowmass dwarf stars, young stellar objects, and numerous other Milky Way and Local Group sources across the entire sky from both hemispheres. In this paper, we describe the APOGEE-2 observational design, target selection catalogs and algorithms, and the targeting-related documentation included in the SDSS data releases.