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Ever since the hydrogen emission line of Lyman-alpha (Ly) has been postulated to hold one of the keys to studying high-redshift galaxies, the question of what emission lines can tell us about the properties and evolution of galaxies has driven much of our research. This work is a survey of emission lines across cosmic history. Just as galaxies evolve with redshift, so does how we can use emission line information from these galaxies. I begin with a study of resolved Ly emission in nearby galaxies, and how we can use pixel-by-pixel photometry to study emission on very small galactic scales and to characterize Ly scattering. Using the Lyman-Alpha Reference Sample, a set of 14 starbursting galaxies with redshifts of 0.02 z
Thoroughly revised and expanded throughout, the new edition is a graduate-level text and reference book on gaseous nebulae, nova and supernova remnants. Much of the new data and new images are from the Hubble Space Telescope with two wholly new chapters being added along with other new features. The previous edition which was tried and tested for thirty years has now been succeeded by a revised, updated, larger edition, which will be valuable to anyone seriously interested in astrophysics.
Our knowledge of galaxy formation and evolution has exploded over the past few decades and we are now in an era of large galaxy surveys consisting of millions of galaxies. These samples enable statistical characterization of galaxy populations, helping to empirically explore the manner in which galaxies evolve through time. Current and future missions will push the envelope further by identifying millions of galaxies, many of which will be selected via their strong emission lines. We are motivated to develop ever-more sophisticated statistical methods to extract the maximal amount of information from these surveys. In Chapter 2, I describe the details of identifying a large sample of z~2 galaxies selected from Hubble Space Telescope (HST) grism frames on the basis of their strong rest-frame optical emission lines, with [O III] being the strongest in the vast majority of these systems. I also present the basis physical properties of the sample, including their rest-frame UV and optical size, stellar mass, UV-based star formation rate (SFR), and dust content. In order to provide context for how this emission-line galaxy (ELG) sample relates to the broader galaxy population at this epoch, I identify a comparison sample selected on the basis of their photometric redshifts and compare the two samples' physical properties. The ELG sample has systematically lower stellar masses, SFRs, and dust contents compared to the photometric redshift sample. This comparison indicates that identifying galaxies on the basis of their strong emission lines is an efficient way to find low-mass systems but is biased against objects with large amounts of dust. In Chapter 3, I measure the luminosity function and star-formation rate density of the sample introduced in Chapter 2. This measurement directly informs the observing strategy that is required for upcoming missions, which will use rest-frame optical ELGs to measure the large scale structure of the Universe. Since the precision in this measurement is directly related to the number of sources that are identified, accurate estimates of the line luminosity function are essential for designing the observing strategies of these flagship missions. I introduce a new, flexible spectral energy distribution (SED) code, MCSED, in Chapter 4. This galaxy fitting tool is specifically optimized to allow for varying assumptions about the physics and interplay of stars, dust, and gas in galaxies. Since the properties of these various components change with redshift and host galaxy type, and are constantly being improved from both an empirical and theoretical standpoint, flexible SED fitting tools are essential for extracting the maximal amount of science from new surveys. I apply this code to the z~2 galaxy sample introduced in Chapter 2 using a flexible model with multiple parameters to describe the dust attenuation and star formation history. The sample exhibits clear evolution in the star formation histories, dust contents, and average spectra across the three orders of magnitude in stellar mass. As the stellar mass increases, the objects become redder due to both a higher dust content and a larger population of old, red stars. Finally, Chapter 5 presents an expanded framework for fitting the SEDs of galaxies that accounts for correlated and non-Gaussian uncertainties in the photometric flux measurements. Such covariances are nearly universal in modern techniques for measuring photometry, yet these correlations have not been taken into account in SED fitting until now. This method for propagating variances and covariances throughout the analysis pipeline will be particularly important for upcoming high-precision cosmology experiments that rely upon photometric redshifts.
As late as 1995, the anticipated widespread population of primeval galaxies remained at large, lurking undetected at unknown redshifts, with undiscovered properties. We present results from our efforts to detect and characterize primeval galaxies by their signature high-redshift Lyman-alpha emission lines utilizing two observational techniques: serendipitous slit spectroscopy and narrowband imaging. By pushing these techniques to their utmost limits, we probe the Lyman-alpha-emitting galaxy population out to redshifts as high as z = 6.5. Galaxies at this epoch reside in a universe which is just 800 million years old, a mere 6% of its current age. As such, this work provides one account of the manner by which observational cosmology has recently shifted from merely marveling at the incredible lookback times implied by the first few high-redshift detections, to the routine assembly of high-redshift datasets designed to address specific astrophysical issues.
The study of galaxies across multiple epochs is essential for understanding the evolution of the universe. One key time period to study is z ∼ 2, when star formation activity in the universe is at its peak. Comparing local galaxies to those in this more active time period is a critical way to learn about galaxy evolution by examining the differences and/or similarities in galaxy properties. In this thesis, I study the rest-frame optical emission-line and host galaxy properties of star-forming galaxies at z ∼ 2 in the MOSFIRE Deep Evolution Field (MOSDEF) survey to better understand the evolution of galaxies over the past 10 Gyr of our universe's history. First, I investigate correlations between the emission-line properties and the physical and chemical properties of z ∼ 2 star-forming galaxies in the MOSDEF survey. It is necessary to understand the known offset of z > 1 galaxies on the [O III][lambda]5008/H[Beta] vs. [N II][lambda]6585/H[alpha] ([N II] "BPT") diagram compared to their local counterparts because strong rest-optical emission-lines are commonly used to infer a variety of galaxy properties (e.g. gas-phase oxygen abundance). To investigate the physical driver of this shift, I defined two populations of z ∼ 2 MOSDEF galaxies on the [N II] BPT diagram, one on and one off (i.e., offset from) the local sequence. I find that these two groups remain separated on the [O III][lambda]5008/H[Beta] vs. [S II][lambda][lambda]6718,6733/H[alpha] ([S II] BPT) diagram and the [O III][lambda][lambda]4960,5008/[O II][lambda][lambda]3727,3730 vs. ([O III][lambda][lambda]4960,5008+[O II][lambda][lambda]3727,3730)/H[Beta] (O 32 vs. R 23 ) diagram, which suggests that star-forming regions in the more offset galaxies are characterized by harder ionizing spectra at fixed nebular oxygen abundance. Such a phenomenon may be tied to [alpha]-enhancement and massive stars that are chemically "young." Second, I compare the z ∼ 2 MOSDEF survey with the z ∼ 2 portion of the Keck Baryonic Structure Survey (KBSS) that has been observed with MOSFIRE. Like MOSDEF, KBSS studies a large sample of star-forming galaxies at z ∼ 2 with the MOSFIRE instrument; however, there are notable differences in survey construction and key results (e.g., the magnitude of the offset from the local star-forming sequence on the [N II] BPT diagram). Using consistent spectral-energy-distribution (SED) modeling for both surveys reveals that the MOSDEF z ∼ 2 targeted sample has a higher median stellar mass, lower star-formation rate (SFR) and specific SFR, and redder U−V color compared to KBSS. However, the subsets of the surveys that have been analyzed in previous work with high S/N spectra and multiple emission lines detected are strikingly similar. Aside from stellar population age, all sample properties investigated agree within the median uncertainties. Additionally, applying uniform stellar Balmer absorption correction and emission-line fitting techniques for both samples results in the same offset on the [N II] BPT diagram. I find that the previously believed differences in key results between the two surveys can be attributed toutilizing different SED and emission-line fitting techniques. Third, I analyze the completeness of the MOSDEF z ∼ 2 survey. Specifically, I use SED modeling and composite spectra created from spectral stacking to test if the subset of the MOSDEF z ∼ 2 star-forming galaxies with high S/N spectra is representative of the complete sample of star-forming galaxies. I find that the host galaxy and emission-line properties (most notably offset from the local SDSS sequence on the [N II] BPT diagram) are very similar, indicating that the smaller spectroscopic samples are representative of the full catalog of star-forming galaxies. Additionally, comparing galaxy properties obtained through SED modeling reveals that the z ∼ 2 sample observed by MOSDEF is representative of all z ∼ 2 galaxies that met the selection criteria for the MOSDEF survey. Taken together, these results reveal that the emission-line trends established using high S/N z ∼ 2 detection samples of star-forming galaxies in MOSDEF studies to date are representative of the rest-optical-magnitude-limited star-forming galaxy population at z ∼ 2. Fourth, I focus on two actively merging galaxies in the MOSDEF survey at z = 1.89. We model the SEDs of the merging galaxies to find that they are both massive with low SFRs and similar stellar population ages. Additionally, the star formation in both galaxies began and peaked within a few hundred Myr of each other, suggesting that their bursts of star formation may be connected. For one of these galaxies, GOODS-S 43114, Sérsic profile fitting and a relatively low velocity dispersion estimate indicates that it is a face-on disk; therefore, it will likely undergo a large structural change as it evolves into a massive, slowly-rotating elliptical galaxy in the present day. Finally, as an earlier part of research I used far-IR Herschel/PACS spectra to investigate the profiles of six OH doublets for a large sample of 178 local galaxies. I assembled ancillary data to probe AGN luminosity, radiation field hardness, dust temperature, and dust obscuration, and find correlations between the EW(OH) and these galaxy observables. Additionally, I comment on how the origin of emission for these OH doublets, whether from radiative pumping by infrared photons or from collisional excitation, may influence these relationships.
Recent observational developments are providing the first truly panchromatic view of galaxies, extending from the radio to TeV gamma-rays. This is motivating the development of new models for the interpretation of spectral energy distributions (SEDs) of galaxies in terms of the formation, evolution and emission of stellar and accretion-driven sources of photons, the interaction of the photons with the gaseous and dust components of the interstellar medium, and high-energy processes involving cosmic rays. IAU Symposium 284 details progress in the development of such models, their relation to fundamental theory, and their application to the interpretation of the panchromatic emission from the Milky Way and nearby galaxies, connecting the latter with models for the evolution of the SEDs of distant galaxies, and the extragalactic background light. IAU S284 is a useful resource for all researchers working with the copious amounts of multiwavelength data for galaxies now becoming available.
The formation and evolution of galaxies is one of the most important topics in modern astrophysics. Secular evolution refers to the relatively slow dynamical evolution due to internal processes induced by a galaxy's spiral arms, bars, galactic winds, black holes and dark matter haloes. It plays an important role in the evolution of spiral galaxies with major consequences for galactic bulges, the transfer of angular momentum, and the distribution of a galaxy's constituent stars, gas and dust. This internal evolution is in turn the key to understanding and testing cosmological models of galaxy formation and evolution. Based on the twenty-third Winter School of the Canary Islands Institute of Astrophysics, this volume presents reviews from nine world-renowned experts on the observational and theoretical research into secular processes, and what these processes can tell us about the structure and formation of galaxies. The volume provides a firm grounding for graduate students and early career researchers working on galactic dynamics and galaxy evolution.
Describing how to investigate all kinds of galaxies through a multifrequency analysis, this text is divided into three different sections. The first describes the data currently available at different frequencies, from X-rays to UV, optical, infrared and radio millimetric and centimetric, while explaining their physical meaning. In the second section, the author explains how these data can be used to determine physical parameters and quantities, such as mass and temperature. The final section is devoted to describing how the derived quantities can be used in a multifrequency analysis to study such physical processes as the star formation cycle and constrain models of galaxy evolution. As a result, observers will be able to interpret galaxies and their structure.
Spectral lines, widths, and shapes are powerful tools for emitting/absorbing gas diagnostics in different astrophysical objects (from the solar system to the most distant objects in the universe—quasars). On the other hand, experimental and theoretical investigations of laboratory plasma have been applied in spectroscopic astrophysical research, especially in research on atomic data needed for line shape calculations. Data on spectral lines and their profiles are also important for diagnostics, analysis, and the modelling of fusion plasma, laser-produced plasma, laser design and development, and various plasmas in industry and technology, like light sources based on plasmas or the welding and piercing of metals by laser-produced plasma. The papers from this book can be divided into four groups: 1. stark broadening data for astrophysical and laboratory plasma investigations; 2. applications of spectral lines for astrophysical and laboratory plasma research; 3. spectral line phenomena in extragalactic objects, and 4. laboratory astrophysics results for spectra investigation. The reviews and research papers, representing new research on the topics presented in this book, are of interest for specialists and PhD students. We hope that the present book will be useful and interesting for scientists interested in the investigation of spectral line shapes and will contribute to the education of young researchers and PhD students.