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Understanding the regulation and environment of star formation across cosmic time is critical to tracing the build-up of mass in the Universe and the interplay between the stars and gas that are the constituents of galaxies. Three studies are presented in this thesis, each examining a different aspect of star formation at a specific epoch. The first study presents the results of a photometric and spectroscopic survey of 321 Lyman break galaxies (LBGs) at z = 3 to investigate systematically the relationship between Ly & alpha; emission and stellar populations. Ly & alpha; equivalent widths were calculated from rest-frame UV spectroscopy and optical/near-infrared/Spitzer photometry was used in population synthesis modeling to derive the key properties of age, dust extinction, star formation rate (SFR), and stellar mass. We directly compare the stellar populations of LBGs with and without strong Ly & alpha; emission, where we designate the former group (Ly & alpha; equivalent widths greater than 20 & Aring;) as Ly & alpha;-emitters (LAEs) and the latter group (Ly & alpha; equivalent widths fewer than 20 & Aring;) as non-LAEs. This controlled method of comparing objects from the same UV luminosity distribution represents an improvement over previous studies in which the stellar populations of LBGs and narrowband-selected LAEs were contrasted, where the latter were often intrinsically fainter in broadband filters by an order of magnitude simply due to different selection criteria. Using a variety of statistical tests, we find that Ly & alpha; equivalent width and age, SFR, and dust extinction, respectively, are significantly correlated in the sense that objects with strong Ly & alpha; emission also tend to be older, lower in star formation rate, and less dusty than objects with weak Ly & alpha; emission, or the line in absorption. We accordingly conclude that, within the LBG sample, objects with strong Ly & alpha; emission represent a later stage of galaxy evolution in which supernovae-induced outflows have reduced the dust covering fraction. We also examined the hypothesis that the attenuation of Ly & alpha; photons is lower than that of the continuum, as proposed by some, but found no evidence to support this picture. The second study focuses specifically on galactic-scale outflowing winds in 72 star-forming galaxies at z = 1 in the Extended Groth Strip. Galaxies were selected from the DEEP2 survey and follow-up LRIS spectroscopy was obtained covering SiII, CIV, FeII, MgII, and MgI lines in the rest-frame ultraviolet. Using GALEX, HST, and Spitzer imaging available for the Extended Groth Strip, we examine galaxies on a per-object basis in order to better understand both the prevalence of galactic outflows at z = 1 and the star-forming and structural properties of objects experiencing outflows. Gas velocities, measured from the centroids of FeII interstellar absorption lines, are found to span the interval -217, +155 km s-1. We find that approximately 40% (10%) of the sample exhibits blueshifted FeII lines at the 1 & sigma; (3 & sigma;) level. We also measure maximal outflow velocities using the profiles of the FeII and MgII lines; we find that MgII frequently traces higher velocity gas than FeII. Using quantitative morphological parameters derived from the HST imaging, we find that mergers are not a prerequisite for driving outflows. More face-on galaxies also show stronger winds than highly inclined systems, consistent with the canonical picture of winds emanating perpendicular to galactic disks. In light of clumpy galaxy morphologies, we develop a new physically-motivated technique for estimating areas corresponding to star formation. We use these area measurements in tandem with GALEX-derived star-formation rates to calculate star-formation rate surface densities. At least 70% of the sample exceeds a star-formation rate surface density of 0.1 solar masses yr-1 kpc-2, the threshold necessary for driving an outflow in local starbursts. At the same time, the outflow detection fraction of only 40% in FeII absorption provides further evidence for an outflow geometry that is not spherically symmetric. We see a 3 & sigma; trend between outflow velocity and star-formation rate surface density, but no significant trend between outflow velocity and star-formation rate. Higher resolution data are needed in order to test the scaling relations between outflow velocity and both star-formation rate and star-formation rate surface density predicted by theory. Galactic winds are further explored in the third study of this thesis, where we present a study at z = 1 of the prevalence and kinematics of ultraviolet emission lines from fine-structure FeII* transitions and resonance MgII transitions. Utilizing a multiwavelength dataset of 212 star-forming galaxies, we investigate how the strength and kinematics of FeII* and MgII emission lines vary as a function of galaxy properties. We find that FeII* emission is prevalent in the sample; composite spectra assembled on the basis of a variety of galaxy properties all show FeII* emission, particularly in the stronger 2396 and 2626 & Aring; lines. This prevalence of emission is in contrast to observations of local galaxies; the lack of FeII* emission in the small star-forming regions targeted by spectroscopic observations at z = 0 may imply that FeII* emission arises in more extended galaxy halos. The strength of FeII* emission is most strongly modulated by star-formation rate, dust attenuation, and [OII] equivalent width, such that systems with lower star-formation rates, lower dust levels, and larger [OII] equivalent widths show stronger FeII* emission. MgII emission, while not observed in a spectral stack of all the data in our sample, is seen in 30% of individual objects. We find that objects showing MgII emission have preferentially larger [OII] equivalent widths, bluer U-B colors, and lower stellar masses than the sample as a whole. Active galactic nuclei are not likely responsible for the MgII emission in our sample, since we have excluded active galaxies from our dataset. We also do not observe the NeV emission line at 3425 & Aring; characteristic of active galaxies in our co-added spectra. We find that the kinematics of FeII* emission lines are consistent with the systemic velocity. This result does not necessarily imply that these lines arise from star-forming regions, however, as an optically thin galactic wind could show blueshifted and redshifted FeII* emission lines centered around 0 km s-1. We note that FeII* emission arising from extended gas is consistent with the hypothesis that slit losses are responsible for the lack of FeII* emission in local samples. We propose that dust is primarily responsible for the correlations between FeII* strength and galaxy properties, as objects with lower star-formation rates and larger [OII] equivalent widths also exhibit lower dust attenuations, on average. The strong MgII emission seen in systems with larger [OII] equivalent widths, bluer U-B colors, and lower stellar masses may also be the result of low dust attenuation in these objects. Larger studies composed of high signal-to-noise observations will be critical for testing the hypothesis that dust is the primary modulator of fine-structure and resonance emission.
This up-to-date reference on stellar populations and development models includes coverage of distant galaxies, chemical evolution and supernovae. Written by highly acclaimed authorities in the field, the book makes use of specific problems to reveal the "kitchen secrets."
The term “chemical evolution of galaxies” refers to the evolution of abundances of chemical species in galaxies, which is due to nuclear processes occurring in stars and to gas flows into and out of galaxies. This book deals with the chemical evolution of galaxies of all morphological types (ellipticals, spirals and irregulars) and stresses the importance of the star formation histories in determining the properties of stellar populations in different galaxies. The topic is approached in a didactical and logical manner via galaxy evolution models which are compared with observational results obtained in the last two decades: The reader is given an introduction to the concept of chemical abundances and learns about the main stellar populations in our Galaxy as well as about the classification of galaxy types and their main observables. In the core of the book, the construction and solution of chemical evolution models are discussed in detail, followed by descriptions and interpretations of observations of the chemical evolution of the Milky Way, spheroidal galaxies, irregular galaxies and of cosmic chemical evolution. The aim of this book is to provide an introduction to students as well as to amend our present ideas in research; the book also summarizes the efforts made by authors in the past several years in order to further future research in the field.
We study the spatially resolved properties of star-forming galaxies at redshift z 2 - 3 on scales 1 kpc using a combination of morphological and kinematic analyses in an effort to characterize the major mechanisms of galaxy formation in the young universe. Using a sample of 216 galaxies which have been spectroscopically confirmed to lie between redshifts z = 1.8 - 3.4 in the GOODS-N field we demonstrate that rest-UV morphology (as seen by the Hubble Space Telescope) is statistically uncorrelated with physical properties such as star formation rate and is therefore unable to support the hypothesis that the prevalence of irregular morphologies indicates a high major merger fraction. Further, we present a sample of 13 galaxies observed with the OSIRIS integral field spectrograph and the Keck laser-guide star adaptive optics system which demonstrate the prevalence of high velocity dispersions 80 km/s and generally little in the way of spatially resolved velocity gradients, inconsistent with favored rotating disk models. We discuss the implications of these results for galaxy formation models, including gas accretion via cold flows and gravitational instability of early gas-rich galactic disks. There is some evidence for a trend towards stronger rotational signatures in galaxies with more massive stellar populations.
This volume presents lectures of the XI Canary Islands Winter School of Astrophysics written by experts in the field.
The 52 papers respond to the explosion of the search for and discovery of high redshift galaxies and the application of broad-band photometry to obtain remarkably reliable estimates of the redshifts of galaxies at all redshifts, spurred not only by the Hubble Deep Fields, but also by the advent of wide-field CCDs on ground-based telescopes and the development of sensitive infrared, submillimeter, and millimeter instrumentation. They discuss techniques, findings, and integrating new data into existing models of galaxy formation and evolution.
The high-redshift galaxies became a distinct research ?eld during the ?nal decade of the20thcentury. AtthattimetheLyman-breaktechniquemadeitpossibletoidentify signi?cant samples of such objects, and the new generation of 8 to 10-m telescopes resulted in ?rst good spectroscopic data. Today the high-redshift galaxies have developed into one of the important topics of astrophysics, accounting for about 5–10% of the publications in the major scienti?c journals devoted to astronomy. Because high-redshift galaxies is a rapidly developing ?eld and since new results are published constantly, writing a book on this topic is challenging. On the other hand, in view of the large amount of individual results now in the literature, and in view of the still growing interest in this topic, it appears worthwhile to summarize and evaluate the available data and to provide an introduction for those who wish to enter this ?eld, or who, for various reasons, might be interested in its results. The end of the ?rst decade of the 21st century appears to be a good point in time to attempt such a summary. The current generation of ground-based 8 to 10-m - optical telescopes, the Hubble Space Telescope, and the most important large radio telescopes have by now been in operation since about one or two decades. Although these instruments will continue to produce important scienti?c results for some time to come, many of the initial programs exploiting their unique new possibilities have been completed.
These proceedings offer professional astronomers an overview of the rapidly advancing subject of galaxy interactions at low and high redshifts. The symposium gave participants an exciting glimpse of a developing synthesis highlighting galactic encounters and their role in the history of the Universe.
IAU Symposium 262 presents reviews on the current understanding of the theories of stellar evolution, galaxy formation and galaxy evolution. It emphasises what we have learned in the past few years from massive surveys covering large portions of the sky (e.g. SDSS, HDF, UDF, GOODS, COSMOS). Several critical aspects of research on stellar populations deserve further effort in order to be brought in tune with other areas of astrophysical research. The next ten years will see the opening of major observatories that will increase the quality and quantity of astronomical data by orders of magnitude. The expected benefits from these instruments for the study of stellar populations are explored. This critical review of state of the art observational and theoretical work will appeal to all those working on stellar populations, from distant galaxies to local resolved galaxies and galactic star clusters.