We present the survey strategy and early results of the "Satellites Around Galactic Analogs" (SAGA) Survey. The SAGA. Survey's goal is to measure the distribution of satellite galaxies around 100 systems analogous to the Milky Way down to the luminosity of the Leo I dwarf galaxy (M-r < -12.3). We define a Milky Way analog based on K-band luminosity and local environment. Here, we present satellite luminosity functions for eight Milky-Way-analog galaxies between 20 and 40. Mpc. These systems have nearly complete spectroscopic coverage of candidate satellites within the projected host virial radius down to r(o) < 20.75 using low-redshift gri color criteria. We have discovered a total of 25 new satellite galaxies: 14. new satellite galaxies meet our formal criteria around our complete host systems, plus 11 additional satellites in either incompletely surveyed hosts or below our formal magnitude limit. Combined with 13 previously known satellites, there are a total of 27 satellites around 8 complete Milky-Way-analog hosts. We find a wide distribution in the number of satellites per host, from 1 to 9, in the luminosity range for which there are 5 Milky Way satellites. Standard abundance matching extrapolated from higher luminosities predicts less scatter between hosts and a steeper luminosity function slope than observed. We find that the majority of satellites (26 of 27) are star-forming. These early results indicate that the Milky Way has a different satellite population than typical in our sample, potentially changing the physical interpretation of measurements based only on the Milky Way's satellite galaxies.

We present a study of the relation between galaxy stellar age and mass for 14 members of the z = 1.62 protocluster IRC 0218, using multiband imaging and HST G102 and G141 grism spectroscopy. Using UVJ colors to separate galaxies into star-forming and quiescent populations, we find that, at stellar masses M*>= 10(10.85)M circle dot the quiescent fraction in the protocluster is f(Q) = 1.0(-0.37)(+0.00), consistent with a similar to 2x enhancement relative to the field value, f(Q) = 0.45(-0.03)(+0.03). At masses 10(10.2)M circle dot <= M* <= 10(10.85)M circle dot, f(Q) in the cluster is f(Q) = 0.40(-0.18)(+0.20), consistent with the field value of f(Q) = 0.28(-0.02)(+0.02). Using galaxy D-n(4000) values derived from the G102 spectroscopy, we find no relation between galaxy stellar age and mass. These results may reflect the impact of merger- driven mass redistribution-which is plausible, as this cluster is known to host many dry mergers. Alternately, they may imply that the trend in f(Q) in IRC 0218 was imprinted over a short timescale in the protocluster's assembly history. Comparing our results with those of other high- redshift studies and studies of clusters at z similar to 1, we determine that our observed relation between f(Q) and stellar mass only mildly evolves between z similar to 1.6 and z similar to 1, and only at stellar masses M* <= 10(10.85) M circle dot Both the z similar to 1 and z similar to 1.6 results are in agreement that the red sequence in dense environments was already populated at high redshift, z greater than or similar to 3, placing constraints on the mechanism(s) responsible for quenching in dense environments at z >= 1.5.

Masters of Science / The study of the faint radio universe and of its properties has recently become a very active field of research not only because of the much improved capabilities of the SKA pathfinders but also because of the need to better plan for SKA surveys. These new facilities will map large areas of the sky to unprecedented depths and transform radio astronomy into the leading technique for investigating the complex processes which govern the formation and evolution of galaxies. This thesis combines multi-wavelength techniques, highly relevant to future deep radio surveys, to study the properties of faint radio sources. The nature of the faint radio sources is presented, over a large GMRT survey area of an area of 1.2 deg2 comprising 2800 sources. Utilising multi-wavelength data we have matched 85% of the radio population to Spitzer/IRAC and obtained a redshift estimate for 63%. The redshift associations are a combination of photometric and spectroscopic redshift estimates. This study investigates several multi-wavelength diagnostics used to identify AGN, using radio, infrared, optical and x-ray data . This analysis shows that various diagnostics (from the radio through the X-ray ones) select fairly different types of AGNs, with an evidence of a disagreement in the number of AGNs selected by each individual diagnostics. For the sources with redshift we use a classification scheme based on radio luminosity, x-ray emission, BOSS/SDSS spectroscopy, IRAC colors satisfying the Donley criterion, and MIPS 24ɥm radio-loud AGN criteria to separate them into AGNs and SFGs. On the basis of this classification, we find that at least 12.5% of the sources with redshifts are AGNs while the remaining 87.5% are adopted as SFGs. We explore the nature of the classified sources through the far-infrared radio correlation. We measure a median qIR value of 2:45± 0:01 for the SFGs and qIR value of 2:27 ± 0:05 for the AGNs. The decrease in the median value of qIR for the AGNs is a result of the additional AGN component to radio emission for the AGN-powered sources and find tentative evidence of an evolution of the qIR with redshift.

Our sensitive (sigma(n) approximate to 572 nJy beam(-1)), high-resolution (FWHM theta(1/2) = 0"22 approximate to 2 kpc at z greater than or similar to 1), 10 GHz image covering a single Karl G.. Jansky Very Large Array (VLA) primary beam (FWHM circle minus(1/2) approximate to 4.'25) in the GOODS-N field contains 32 sources with S-p greater than or similar to 2 mu Jy beam(-1) and optical and/or near-infrared (OIR) counterparts. Most are about as large as the star-forming regions that power them. Their median FWHM major axis is <theta(M)>= 167 +/- 32 mas approximate to 1.2 +/- 0.28 kpc, with rms scatter approximate to 91 mas approximate to 0.79 kpc. In units of the effective radius re that encloses half their flux, these radio sizes are re approximate to 69 +/- 13 mas approximate to 509 +/- 114 pc, with rms scatter approximate to 38 mas approximate to 324 pc. These sizes are smaller than those measured at lower radio frequencies, but agree with dust emission sizes measured at mm/sub-mm wavelengths and extinction-corrected H alpha sizes. We made a lowresolution (theta(1/2) = 1."0) image with approximate to 10x better brightness sensitivity, in order to detect extended sources and measure matched-resolution spectral indices alpha(10 GHz)(1.4 GHz) 10 GHz. It contains six new sources with Sp. 3.9 mJy beam-1 and OIR counterparts. The median redshift of all 38 sources is similar to z similar to = 1.24 +/- 0.15. The 19 sources with 1.4 GHz counterparts have a median spectral index of <alpha(1.4 GHz) (10 GHz)> = -0.74 +/- 0.10 10 GHz, with rms scatter approximate to 0.35. Including upper limits on a for sources not detected at 1.4 GHz flattens the median to <alpha(1.4 GHz) (10 GHz)> greater than or similar to -0.61 10 GHz, suggesting that the mu Jy radio sources at higher redshifts-and hence those selected at higher rest-frame frequencies-may have flatter spectra. If the non-thermal spectral index is alpha(NT) approximate to -0.85, the median thermal fraction of sources selected at median rest-frame frequency approximate to 20 GHz is greater than or similar to 48%.

New techniques are developed for relating the statistics of close galaxy pairs to the galaxy merger and accretion rates. Unlike the traditional pair fraction approach, these methods are shown to be robust to a number of selection effects related to the depth and completeness of the sample. These techniques are applied to the large, well-defined SSRS2 (z ∼ 0) and CNOC2 (0.1 ≤ ± ≤ 0.55) redshift surveys, yielding the first secure measurements of close pair statistics at low and moderate redshift. These results imply that the galaxy merger and accretion rates increase with redshift, approximately as (1 + z)2±1.5, for galaxies brighter than MB = –18. The CNOC2 survey is used to carry out a detailed comparison between close companions and field galaxies. Paired galaxies are found to be of slightly earlier spectral type, with a larger spread in properties. In particular, the spectral indices of close companions imply a more complex star formation history, as would be expected if galaxy interactions and mergers are prevalent. / Graduate

In this thesis we investigate the evolution of galaxies since z = 3. There are several methods to measure the star formation rate (SFR) of galaxies, they all however have drawbacks. Several studies have investigated the SFR at high redshifts using SFR trac­ers that suffer from uncertainties, either from the tracer used, or from the uncertainties correcting for the effects of dust. We have new measurements of the Ha emission line for a sample of galaxies at =~1; Ha is a more accurate SFR-tracer than other com­monly used tracers, but until now had been technically difficult to measure at : > 0.85. We investigate methods to correct these observations for dust and we use these mea­surements to investigate the relation between SFR, stellar mass and colour. We find that there is a drop in the fraction of massive (M, > 1011 M.) star-forming galaxies at = < 0.9 and that the fraction of all galaxies that are star-forming drops steadily and significantly with redder (U — B) colours. We find that the M„-SFR (galaxy main sequence, GMS) is flatter than previously measured and that for the most massive galaxies, star formation shuts off abruptly at =~1.

Dynamical models of Seyfert nuclei and quasi-stellar objects are presented. The central energy source often postulated for these active objects provides a means of heating and ionizing the nuclear gas, and also exerts an outward force on the gas. Since the gas will be fully ionized, it will be nearly transparent to X-rays, while cosmic rays will interact strongly with it. Preliminary calculations of this "ionization" pressure on discrete clouds show that photons are unlikely to produce the high gas velocities relative to the nucleus which are indicated by the emission line profiles in Seyfert nuclei and the blueshifted quasar absorption lines, but that cosmic rays can accelerate the clouds up to these velocities. A more detailed calculation taking into account the dynamics of the gas is called for. A computer code was written to solve the spherically symmetric hydrodynaraic equations numerically. It uses a finite difference, implicit Eulerian scheme to solve the time dependent equations. As well as the mass conservation and momentum transfer equations, the numerical system includes an energy equation which allows for ionization and Coulomb heating, and radiative cooling. The code was used to obtain a set of nuclear evolutionary models. These models involve a static gas surrounding a quiescent energy source which turns on suddenly. A range of input physical parameters is represented: for sizes 0.1 to 1 pc, a total cosmic ray flux from 10⁴³ ergs s⁻¹ to 10⁴⁸ ergs s⁻¹, a gas density of 10⁴ to 10⁸ cm⁻³, a lowest particle energy in a power law spectrum of 0.1 to 10.0 MeV, and a central mass of 10⁸ or 10⁹ M⃙. Such soft cosmic rays have a very short absorption length in the nuclear gas. This means a narrow region in radial extent will gain the momentum of the cosmic ray beam, and an outward moving shell will form. It snowplows the cooler gas ahead of it and leaves a less dense, hot cavity behind. This thin cavity reaches temperatures of 10⁸ K, and the dense shell reaches an equilibrium temperature in the range 10⁴-10⁵ K. The shell velocities increased as the cosmic ray flux was increased, ranging from 500 to 8000 km s⁻¹. The lifetime of this phenomenon is the time for the shell to escape the nuclear region, which is only a few parsecs across. At these velocities, the timescale is only 10³ to 10⁴ years. This suggests repetitive rather than continuous activity of the central source. A quiescent phase would allow replenishment of the gas from extra-nuclear stellar sources. The interface between the hot cavity and the shell is Rayleigh-Taylor unstable with a fragmentation time approximately equal to the shell escape time. This may explain the cloud structure observed in these objects. Thermal instabilities may also arise if the central source turns off. Prediction of the sources of the permitted and forbidden emission lines is dependent on the behavior of the instabilities. The very dense shell suggests a physical distinction between the regions producing the two types of spectra, which may explain the wider permitted lines in some sources. The hot gas near the energy source will produce thermal X-rays. The luminosity and temperature predicted for the X-rays is consistent with observations. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Two dimensional photometry of NGC 1068 and NGC 1566 at visual and red wavelengths has been obtained. An H⍺ image of NGC 1068 has also been obtained. Decomposition of the luminosity profiles derived from the data shows that the inner region (r<18") of NGC 1566 consists of a nuclear point source component, a spheroidal bulge, and an exponential disk. Colors for each component are derived which show that the disk is redder at the outer edge than at the center The point source component is quite weak, contributing only 5% of the total light in an 8.5 aperture. A color map is also presented, showing an enhancement of red emission in the center and at the outer edges of the image. For NGC 1068, the profiles permit a bulge component to be determined for r<11". Subtraction of the seeing convolved bulge reveals a point source component in the red image. This feature is not observed in the visual image, due to obscuration by dust. The color map for NGC 1068 shows a strong color gradient in that the central region is much redder than the outer region, for r<18". There is also an enhancement in red light along the major axis that may describe a bar-like component. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

abstract: A key open problem within galaxy evolution is to understand the evolution of galaxies towards quiescence. This work investigates the suppression of star-formation through shocks and turbulence at low-redshift, and at higher-redshifts, this work investigates the use of features within quiescent galaxy spectra to redshift estimation, and passive evolution of aging stellar populations to understand their star-formation histories. At low-$z$, this work focuses on the analysis of optical integral field spectroscopy data of a nearby ($z\sim0.0145$) unusual merging system, called the Taffy system because of radio emission that stretches between the two galaxies. This system, although a recent major-merger of gas-rich spirals, exhibits an atypically low star-formation rate and infrared luminosity. Strong evidence of shock heating as a mechanism for these atypical properties is presented. This result (in conjunction with many others) from the nearby Universe provides evidence for shocks and turbulence, perhaps due to mergers, as an effective feedback mechanism for the suppression of star-formation. At intermediate and higher-$z$, this work focuses on the analysis of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) G800L grism spectroscopy and photometry of galaxies with a discernible 4000\AA\ break. The usefulness of 4000\AA/Balmer breaks as redshift indicators by comparing photometric, grism, and spectrophotometric redshifts (SPZs) to ground-based spectroscopic redshifts, is quantified. A spectral energy distribution (SED) fitting pipeline that is optimized for combined HST grism and photometric data, developed for this project, is presented. This pipeline is a template-fitting based routine which accounts for correlated data between neighboring points within grism spectra via the covariance matrix formalism, and also accounts for galaxy morphology along the dispersion direction. Evidence is provided showing that SPZs typically improve the accuracy of photometric redshifts by $\sim$17--60\%. For future space-based observatories like the Nancy Grace Roman Space Telescope (formerly the Wide Field InfraRed Survey Telescope, i.e., WFIRST) and Euclid, this work predicts $\sim$700--4400 galaxies\,degree$^{-2}$, within $1.6 \lesssim z \lesssim 3.4$, for galaxies with 4000\AA\ breaks and continuum-based redshifts accurate to $\lesssim$2\%. This work also investigates the star-formation histories of massive galaxies ($\mathrm{M_s \geq 10^{10.5}\, M_\odot}$). This is done through the analysis of the strength of the Magnesium absorption feature, Mgb, at $\sim$5175\AA. This analysis is carried out on stacks of HST ACS G800L grism data, stacked for galaxies binned on a color vs stellar mass plane. / Dissertation/Thesis / Doctoral Dissertation Astrophysics and Astronomy 2020

We have conducted a statistical analysis of the ultra-luminous X-ray point sources (ULXs; L X ≥ 10 39 ergs -1) in a sample of galaxies selected from the Arp Atlas of Peculiar Galaxies. We find a possible enhancement of a factor of 2-4 in the number of ULXs per blue luminosity for the strongly interacting subset. Such an enhancement would be expected if ULX production is related to star formation, as interacting galaxies tend to have enhanced star formation rates on average. For most of the Arp galaxies in our sample, the total number of ULXs compared to the far-infrared luminosity is consistent with values found earlier for spiral galaxies. This suggests that for these galaxies, ULXs trace recent star formation. However, for the most infrared-luminous galaxies, we find a deficiency of ULXs compared to the infrared luminosity. For these very infrared-luminous galaxies, active galactic nuclei may contribute to powering the far-infrared; alternatively, ULXs may be highly obscured in the X-ray in these galaxies and therefore not detected by these Chandra observations. We determined local UV/optical colors within the galaxies in the vicinity of the candidate ULXs using Galaxy Evolution Explorer UV and Sloan Digitized Sky Survey optical images. In most cases, the distributions of colors are similar to the global colors of interacting galaxies. However, the u - g and r - i colors at the ULX locations tend to be bluer on average than these global colors, suggesting that ULXs are preferentially found in regions with young stellar populations. In the Arp sample there is a possible enhancement of a factor of 2-5 in the fraction of galactic nuclei that are X-ray-bright compared to more normal spirals.