This thesis presents new 450$\mu$m and 850$\mu$m observations of NGC3627 taken with the new SCUBA-2 with the main goal of trying to better understand the properties of gas and dust in the interstellar medium of NGC3627. We determined properties of the cold component of NGC3627's spectral energy distribution (SED) using dust models given by the Planck Collaboration, by Li and Draine, and allowing the emissivity index to be treated as a free parameter. Fitting the SED required the use of 100$\mu$m, 160$\mu$m, 250$\mu$m, 350$\mu$m, and 500$\mu$m data from the KINGFISH survey. Each of the KINGFISH observations have been passed through an extended emission filter in order to match the SCUBA-2 observations. The best fit temperatures and emissivity indices agreed with the results found in other recent studies, but our fitted masses were smaller than those of other studies due to differences in the fitted temperature and observed fluxes. After the properties of the dust emission were calculated, we implemented a method to determine the amount of molecular hydrogen present in NGC3627. The method we used involves finding a CO-to-H$_2$ conversion factor that minimizes the scatter present in dust-to-gas mass ratio. We used CO J=2-1 from the HERACLES survey and CO J=1-0 from the Nobeyama 45-m telescope to act as our molecular tracer, and HI observations of NGC3627 from the THINGS survey. The results from minimizing the dust-to-gas ratio scatter give low $\alpha_{CO}$ values, that are normally associated with U/LIRGs. The low $\alpha_{CO}$ values can be attributed to the treatment of the error associated with reported $\alpha_{CO}$. The uncertainties for $\alpha_{CO}$ reported in this thesis are a minimum estimate, and if the error associated with $\alpha_{CO}$ is large enough, then the best fit $\alpha_{CO}$ values can be considered as a lower threshold for the system. / Thesis / Master of Science (MSc)

The relationship first pointed out by Tully and Fisher between the luminosity of spiral galaxies and their maximum rotation velocity, as measured by the 21 cm line-width, continues to be one of the best methods available to measure relative distances. At infrared wavelengths, the observational scatter about this relation is typically 0.35 to 0.50 magnitudes, permitting relative distance estimates with an accuracy of about 20 percent. The Malmquist bias in a magnitude-limited sample is 1.38σ ², and while the solution to the general problem is complex, it is clear that reducing the scatter about the Tully-Fisher relation by even a factor of two would make a large difference in our ability to determine the local velocity field from distances and velocities of individual galaxies. In this dissertation we discuss the scatter in the Tully-Fisher relation at infrared wavelengths, and look for ways to reduce that dispersion through the inclusion of additional observational parameters. The data for this study are derived from a CCD survey of 244 spiral galaxies in twenty clusters falling in the redshift range 3,000 to 11,000 km s⁻¹. From surface brightness profiles and elliptical aperture photometry, we obtained isophotal and total magnitudes at B, R, and I, isophotal diameters, mean and nuclear surface brightnesses, and a concentration parameter indicative of the bulge-to-disk ratio. These quantities were then combined with colors and HI-content measures taken from the literature in a search for correlations with Tully-Fisher residuals. None of the trial second-parameters resulted in a substantial decrease in the scatter about the fiducial Tully-Fisher relation. An examination of the properties of the cluster samples shows that many of the clusters exhibit considerable substructure. While it is possible that the implied depth effects are important to the scatter about the magnitude/line-width relation, calculated lower limits to the dispersion in depth turn out to be rather small.

Thesis advisor: Kevin Bedell / Thesis advisor: Giovanni Fazio / One of the most exciting observational breakthrough in the past decades is the discovery of the tight correlations between supermassive black holes (SMBHs) and the galaxies they reside in the `host galaxies'. This finding is surprising, as the event horizon of a typical SMBH (about 10^8 solar masses) is about 3 times 10^8 km, while the galaxy is usually about 10^17 km across, a billion times larger. How could such a small object affect something so big? SMBHs appear to be at the center of most massive galaxies, and how they interact with the host galaxies has become a fundamental question in astrophysics. To understand how galaxies and SMBHs evolve together, we must first understand the statistical properties of these systems. Quasars, the bright manifestation of the most active SMBHs, serve as good candidate for this study. Using infrared space telescopes--Spitzer and Herschel, we discovered a population of `dust-rich' quasars at intermediate redshift (z about 1.5, about 9 billion years ago) in the Lockman Hole field. We study the statistical properties of these mid-infrared (MIR) and optically-selected quasars via optical and infrared observations. I present the MIR-selected quasar sample (Chapter 2), their addition to the completeness of optically-selected sample (Chapter 3), and their physical properties, i.e., their atomic emission and absorption features, SMBH masses, and Eddington ratios--an indicator of how fast the SMBH is growing (Chapter 4). We find a significant and constant (20%) fraction of extended objects previously missed optical color selection. The SMBH mass shows evidence of downsizing--they are more massive in the early universe, though their Eddington ratios remain constant to between now and about 11 billion years ago (0 lower than z lower than 3). In the past 7 billion years (z lower than 1), quasars with extended morphology show systematically lower Eddington ratios than the point-like quasars, indicating they have less active SMBHs. We also study the spectral energy distributions (SEDs) of a subsample of `cold-dust-rich' quasars (Chapter 5) that show evidence of ongoing star formation--an indicator of how fast the host galaxy is growing. These quasars are the younger and fainter counterparts of quasars previously observed in the sub-millimeter band, as both are bright in the far-infrared, where star formation dominates. For the most luminous cold-dust-rich quasars, however, their infrared SED suggests that the dust is heated by quasars, instead of star formation in the host galaxies. Chapter 6 gives a summary of this study and comment on the significance of the dust-rich quasars in bridging the gap between SMBHs with their host galaxies. Finally some avenues for future work are discussed. / Thesis (PhD) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

The PPAK Integral Field Spectroscopy (IFS) Nearby Galaxies Survey: PINGS, a 2-dimensional spectroscopic mosaicking of 17 nearby disk galaxies in the optical wavelength range. This project represents the first attempt to obtain continuous coverage spectra of the whole surface of a galaxy in the nearby universe. The final data set comprises more than 50000 individual spectra, covering in total an observed area of nearly 80 arcmin square. The powerful capabilities of wide-field 2D spectroscopic studies areproven. The chemical composition of the whole surface of a spiral galaxy ischaracterised for the first time as a function not only of radius, but of theintrinsic morphology of the galaxy, allowing a more realistic determination oftheir physical properties. The methodology, analysis and results of thisdissertation will hopefully contribute in a significant way to understand thenature of the physical and chemical properties of the gas phase in spiralgalaxies.

Active galactic nuclei (AGN) jets are energetic phenomena where twin jets of plasma emerge perpendicular to the plane of the accretion disk surrounding supermassive black holes in galactic centers. Radio-loud jets are largely divided into classes based on the angle of observation (blazars versus radio galaxies), spectral line widths (Flat Spectrum Radio Quasars/FSRQs versus BL Lac objects/BL Lacs), and location of the synchrotron peak frequency in their spectral energy distribution (high-spectral peaked/HSP, intermediate-spectral peaked/ISP, or low-spectral peaked/LSP).<br><br>The linear fractional polarization of the radio emission and the direction of the polarization plan (electric vector position angle, "EVPA'') can be measured, providing information on the properties of the jets' magnetic field. This study uses and describes some processing of data from the MOJAVE program, taken with the VLBA at 15 GHz, to investigate the polarization behavior of 387 AGN. <br><br>The most polarized jets have good alignment between the EVPA and the local jet direction, and higher stability in both fractional polarization and the EVPA. This characterization best describes BL Lacs, which are notably different from FSRQs. HSP BL Lacs have lower fractional polarization than LSP BL Lacs, with fractional polarization partially dependent on apparent jet speeds. These results have supported a scenario where HSP BL Lacs and LSP BL Lacs are similar objects with differing relativistic beaming factors, while FSRQs and BL Lacs as a class have inherent differences in the makeup of their magnetic fields.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. August 2015. / This work investigates the impact of the extragalactic background light fluctuations on very high energy !-ray spectra from distant blazars. We calculate the extragalactic background light spectral energy distribution using a model that extends those proposed by Razzaque et al. (2009ApJ.697.483R) and Finke et al. (2010ApJ.712.238F). We introduce a model for fluctuations in the extragalactic background light based on fluctuations in the star formation rate density, since these two fluctuations can reasonably be expected to be correlated. Fluctuations in the star formation rate are estimated from the semi-analytical galaxy catalogue of Guo et al. (2013MNRAS.428.1351G), we use his model to derive the resulting opacities for !-rays from distant sources. We determine the mean, lower and upper limits for the scatter of the star formation rate density, which then allow us to compute corresponding limits on the extragalactic background light spectrum. We then calculate the impact of these fluctuations limits on the !-ray optical depth. This appears to be the first detailed analytical model that aims to account for the impact of extragalactic background light fluctuations on the !-ray opacity. The model predicts relatively high variations ( 15%) on the opacity in the energy range less than 100 GeV for nearby sources. The impact is found to be smaller (⇠ 5%) for very high energy !-rays from distant sources.

La détermination de ces processus et de leur efficacité est parmi les questions les plus importantes dans notre compréhension de la formation d'étoiles. Le présent travail étudie les lois de formation d'étoiles dans un large éventail de conditions physiques et dynamiques, y compris dans des environnements de faible densité et jusqu'à des échelles de nuages moléculaires, ainsi que des galaxies à grand redshift, pour explorer l'histoire cosmique de la formation des étoiles.Les environnements à faible densité, comme les parties externes des disques des galaxies, imitent les conditions physiques des galaxies naines et aussi celle des galaxies de l'Univers primordial. Au cours du temps de Hubble, il y a eu un pic dans le taux de formation d'étoiles, à z ~ 1-2, il y a environ dix milliards d'années. Ensuite, le taux moyen de formation d'étoiles a chuté drastiquement d'un facteur 20 jusqu'au taux actuel. Cette thèse se concentre sur l'efficacité de la formation des étoiles dans deux contextes : dans les environnements de faible densité, comme les disques externes des galaxies et à l'époque du maximum de la formation d'étoiles cosmique. / Perhaps one of the most enigmatic domains of astrophysics is that of galaxy formation and evolution.A galaxy is defined by its stellar and gas contents. Hence, any theory of galaxy formation has to address the question of the formation of stars.Observations show that star formation takes place in dense molecular clouds.Therefore, the efficiency of star formation of a galaxy is determined by its ability to form molecular clouds.The determination of these processes and their efficiency is among the most important issues in our understanding of star formation.The present work studies the star formation laws in a wide range of physical and dynamical conditions, even in low density environmentsand down to molecular cloud scales, as well as high redshift galaxies, to explore the cosmic star formation history.Low density environments, like the outermost disk of galaxies mimic the physical conditions of dwarf galaxies and also that of galaxiesin the early Universe. Across the Hubble time, there was a peak in the star formation rate, at z ~1-2, about ten billions years ago. Then the average star formation rate dropped by a factor 20 down to the present rate. This Ph.D focuses on the star formation efficiency in two contexts: in low environments, like outer galaxy disks and at the epoch the near the peak of star formation.

What drives the transition of galaxies from the disc dominated, star forming blue cloud to the elliptical dominated, quiescent red sequence? What role does the morphology, central supermassive black hole and galaxy environment play in this transition? I have attempted to answer these questions by using Bayesian statistics to infer a simple star formation history (SFH) describing the time, t_q, and exponential rate, &tau;, that quenching occurs in a galaxy. I use both the optical and NUV photometry of a galaxy in order to infer the posterior distribution of its SFH across the two dimensional [t_q, &tau;] parameter space. I then utilise the Galaxy Zoo 2 morphological classifications to obtain a morphology weighted, combined population distribution across each quenching parameter for a sample of galaxies. I apply this method across the blue cloud, green valley and red sequence of a sample of 126,316 galaxies and find a clear difference between the quenching timescales preferred by smooth and disc weighted populations, with three major routes through the green valley dominated by smooth (rapid rates, attributed to major mergers), intermediately classified (intermediate rates, attributed to galaxy interactions) and disc morphologies (slow rates, attributed to secular evolution). I hypothesise that morphological changes occur in systems which have undergone quenching with an exponential rate, &tau; &LT; 1.5 Gyr, in order for the evolution of galaxies in the green valley to match the ratio of smooth to disc galaxies observed in the red sequence. I repeat this SFH analysis for a sample of 1,244 Type 2 AGN host galaxies and find statistical evidence for recent, rapid quenching, suggesting that this may be caused by AGN feedback. However I find that rapid quenching rates cannot account for all the quenching across the AGN host population; slow quenching rates, attributed to secular evolution, are also significant in the evolution of AGN host galaxies. I investigate this possible secular co-evolution of galaxies and black holes further by measuring the black hole masses of a sample of 101 bulgeless AGN host galaxies and compare them to typical black hole-galaxy scaling relations. I find that the measured black holes of the bulgeless galaxies are ~1-2 dex more massive than they should be, given their lack of bulges. This suggests that black hole-galaxy scaling relations may arise due to mutual correlations to the overall gravitational potential of the dark matter halo of the galaxy. I also considered the effect of the group environment on the time and rate that quenching occurs, with respect to the group-centric radius, for 4,629 satellite galaxies. I find that although mergers, mass quenching and morphological quenching are all occurring in groups, environmentally driven quenching mechanisms are also prevalent. However, I find that these environmentally driven quenching processes are not correlated with the velocity of a satellite within a group, ruling out ram pressure stripping as a possible mechanism. I discuss how all of these quenching mechanisms are likely to affect a galaxy across its lifetime, acting in concert to reduce the SFR, which in turn produces the wide distribution of quenching timescales seen across the colour-magnitude diagram. I discuss ideas for future work using the method employed in this work, including applying it to forthcoming data from large integral field unit surveys.

The near- through mid-infrared offers a unique and, as this thesis aims to show, essential view of extragalactic stellar populations both nearby, at intermediate redshifts and at very high redshift. In chapter 2, I demonstrate that rest-frame near-IR photometry obtained by the Spitzer Space Telescope provides more robust stellar mass estimates for a spectroscopic sample of ~100 galaxies in the redshift desert (0.5<z<2), and is crucial for modeling galaxies with young star-forming populations. From this analysis, a surprising result emerges in the data. Although the rest-frame light short of 2 micron improves stellar mass estimates, the models and observations disagree beyond 2 micron and emission from non-stellar sources becomes significant. At wavelengths from 1-30 micron, stellar and non-stellar emission contribute equally to a galaxy's global spectral energy distribution. This is unlike visible wavelengths where stellar emission dominates or the far-IR where dust emission provides the bulk of a galaxy's luminosity. Using the sample of high-z galaxies, in chapter 3, I quantify the statistical significance of the excess emission at 2-5 micron and find the emission to correlate with the OII luminosity, suggesting a link between the excess emission and star formation. The origin of the excess emission is not clear, although I explore a number of non-stellar candidates in this chapter. Nearby resolved observations provide a clearer picture of the excess by spatially resolving 68 nearby galaxies. By analyzing the pixel-by-pixel near-IR colours within each galaxy at ~1-5 micron, increasingly red near-IR colors are mapped to spatial regions in chapter 4. For regions with red NIR colors and high star formation rates, I find the broad near- through mid-IR spectrum is constant, varying only in amplitude as a function of the intensity of star formation, suggesting the infrared emission of a young, dusty stellar populations can be added to stellar population synthesis models as an additional component tied to the star formation rate. In closing the thesis, the focus is moved to the detection of stellar populations in the earliest star-forming galaxies. By z>6, all visible wavelength emission is redshifted into near-IR wavelengths. In chapter 5, I show how a tunable near-IR filter I have helped develop holds promise for finding bright Lyman alpha emitting galaxies at redshifts of 8<z<11.

The near- through mid-infrared offers a unique and, as this thesis aims to show, essential view of extragalactic stellar populations both nearby, at intermediate redshifts and at very high redshift. In chapter 2, I demonstrate that rest-frame near-IR photometry obtained by the Spitzer Space Telescope provides more robust stellar mass estimates for a spectroscopic sample of ~100 galaxies in the redshift desert (0.5<z<2), and is crucial for modeling galaxies with young star-forming populations. From this analysis, a surprising result emerges in the data. Although the rest-frame light short of 2 micron improves stellar mass estimates, the models and observations disagree beyond 2 micron and emission from non-stellar sources becomes significant. At wavelengths from 1-30 micron, stellar and non-stellar emission contribute equally to a galaxy's global spectral energy distribution. This is unlike visible wavelengths where stellar emission dominates or the far-IR where dust emission provides the bulk of a galaxy's luminosity. Using the sample of high-z galaxies, in chapter 3, I quantify the statistical significance of the excess emission at 2-5 micron and find the emission to correlate with the OII luminosity, suggesting a link between the excess emission and star formation. The origin of the excess emission is not clear, although I explore a number of non-stellar candidates in this chapter. Nearby resolved observations provide a clearer picture of the excess by spatially resolving 68 nearby galaxies. By analyzing the pixel-by-pixel near-IR colours within each galaxy at ~1-5 micron, increasingly red near-IR colors are mapped to spatial regions in chapter 4. For regions with red NIR colors and high star formation rates, I find the broad near- through mid-IR spectrum is constant, varying only in amplitude as a function of the intensity of star formation, suggesting the infrared emission of a young, dusty stellar populations can be added to stellar population synthesis models as an additional component tied to the star formation rate. In closing the thesis, the focus is moved to the detection of stellar populations in the earliest star-forming galaxies. By z>6, all visible wavelength emission is redshifted into near-IR wavelengths. In chapter 5, I show how a tunable near-IR filter I have helped develop holds promise for finding bright Lyman alpha emitting galaxies at redshifts of 8<z<11.