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I use observational evidence to examine the nature and role in galaxy evolution of a population of dust-obscured galaxies (DOGs) at z ∼ 2. These objects are selected with the Spitzer Space Telescope, are bright in the mid-infrared (mid-IR) but faint in the optical, and contribute a significant fraction of the luminosity density in the universe at z ∼ 2. The first component of my thesis is a morphological study using high spatial resolution imaging with the Hubble Space Telescope of two samples of DOGs. One set of 33 DOGs have mid-IR spectral features typical of an obscured active galactic nucleus (AGN) (called power-law DOGs), while the other set of 20 DOGs have a local maximum in their spectral energy distribution (SED) at rest-frame 1.6μm associated with stellar emission (called bump DOGs). The host galaxy dominates the light profile in all but two of these DOGs. In addition, bump DOGs are larger than power-law DOGs and exhibit more diffuse and irregular morphologies; these trends are consistent with expectations from simulations of major mergers in which bump DOGs evolve into power-law DOGs. The second component of my thesis is a study of the dust properties of DOGs, using sub-mm imaging of 12 power-law DOGs. These power-law DOGs are hyper- luminous (2 × 10¹³ L⊙) and have predominantly warm dust (T(dust) > 35 - 60 K). These results are consistent with an evolutionary sequence in which power-law DOGs represent a brief but important phase when AGN feedback heats the interstellar medium and quenches star-formation. The third component of my thesis is a study of the stellar masses and star- formation histories of DOGs, using stellar population synthesis models and broad- band photometry in the rest-frame ultra-violet, optical, and near-IR. The best-fit quantities indicate bump DOGs are less massive than power-law DOGs. The relatively low stellar masses found from this line of analysis favor a merger-driven origin for ULIRGs at z ∼ 2.

Agave adaptation to aridity is examined, comparing trends among phylads, clines in Deserticolae taxa of Baja California, and variation in A. deserti along an elevational gradient. Agave physiology is reviewed and recent evolutionary scenarios are discussed. Tentative hypotheses predict characteristics of Agave leaves and rosettes in arid climates. A study of bioclimatology in the Vizcaino Region of Baja California follows, aimed at defining aspects of a subtropical arid climate that are relevant to a plant. The Vizcaino Region is described in terms of its physiography, vegetation physiognomy and floristics. Ombrothermic diagrams and juxtaposed graphs relate temperature and rainfall at stations throughout the region. Temperature regimes are compared using the 5th, 25th, 75th, and 95th percentiles of their respective distributions of monthly means, and subregional groups with similar regimes are defined. Conditions when soil moisture is available are examined by segregating 'wet' months with rainfall totals of 5 mm or more. Thermal distributions of wet months are compared with respect to their shapes and to temperatures delimiting the central two-thirds of wet months. Patterns in mean annual precipitation are presented. Variables are derived to estimate stress imposed on plants by drought. Median annual precipitation deficit, defined as the difference between total annual potential evapotranspiration and total annual rainfall, expresses the stress typically experienced by plants. The 90th percentile of potential evapotranspiration of dry intervals estimates the severity of droughts that longer-lived perennials survive. Each derived climate variable shows a different geographic pattern. Variance in leaf measurements from collection sites throughout the range of Agave cerulata is studied with a principal components analysis. Leaf characters associated with the major components of variance together with leaf volume/surface ratios are used as dependent variables in multiple regression equations with climate variables, which are estimated for each collection site. As the precipitation deficit increases, leaf size generally decreases, but where the longest droughts are most stressful, leaves tend to be larger. Leaf volume/surface is coupled with leaf size. When size variables are included in regressions, higher volume/surface is associated with more extreme cold, cooler summers, and warmer winters. Warmer summers, higher precipitation deficits, and more warm-season storms are correlated with higher length/width ratios. Larger basal surfaces occur in conjunction with higher precipitation deficits, warmer temperatures, and less warm-season rainfall.

The results of a multi-faceted search for spectral line emission from galaxies at high redshift are presented. Deep two-dimensional spectra of four blank sky fields were taken at the Multiple Mirror Telescope (MMT) at wavelengths corresponding to redshifted Lyα emission in the range 2.7 < z < 4.7, and the resulting non-detections are used to place upper limits on the space density of randomly distributed Lyα emitters. Although the predictions of a conservative model of galaxy formation incorporating cold dark matter are not excluded in a statistical sense, the search would have detected star-forming dwarf galaxies comparable to the Magellanic Clouds at z = 3, given minimal extinction by dust. The Goddard Fabry-Perot Imager, a piezo-electrically controlled tunable narrow-band filter system with a stand-alone CCD system, was developed and tested, and used at the Kitt Peak National Observatory (KPNO) 4 m telescope to image the damped Lyα absorbing clouds towards three high-redshift QSOs in the light of redshifted Lyα. A companion galaxy to one of the damped systems was discovered and confirmed with followup spectroscopy, and its properties are presented and discussed; the companion exhibits strong Lyα and weak C IV λ1549 and He II λ1640 emission lines, and is apparently producing stars at a rate SFR ∼ 5 - 10M(⊙) yr⁻¹. The implications of the companion's proximity to the damped cloud are analyzed in view of the previous non-detections, and a lower limit to the spatial correlation function of the damped Lyα systems with galaxies is given. Spectroscopic limits on Lyα emission from seven damped systems, including some known to have low chemical and dust abundances, imply low levels of star formation, SFR ≲ 1 M(⊙) yr⁻¹, but extinction by dust in some cases may cause an underestimation of these rates. With near-infrared spectrographs at the MMT and the KPNO 4 m, eight damped Lyα systems were searched for spectral lines characteristic of star formation regions but redshifted from the optical into the near-infrared. A possible detection of (O II) λ3727 and Hβ from one system implies a star formation rate on the order of 100 M(⊙) yr⁻¹, though the remainder of the observations produced non-detections compatible with the Lyα emission limits. The implications for galaxy formation and evolution at high redshift are discussed.

Members of multi-specific DNA-binding protein families have evolved to specifically recognize diverse DNA site sequences. This dissertation presents evidence that the Cro protein family of helix-turn-helix transcription factors from lambdoid bacteriophages may share a conserved, limited "code" that partially governs evolution of their binding specificity. A bioinformatic study revealed six conserved sequence correlations between residues at three positions in Cro recognition helices and three base-pairs in putative cognate DNA consensus half-sites (Chapter 2). Three of these pairings correspond to sequence-specific contacts observed at the binding interface of lambda Cro and consensus operator DNA in a previously available co-crystal structure (Albright and Matthews, 1998a). In vitro mutagenesis and functional characterization was used to validate the proposed "code" (Chapter 3). Two out of three "coding" combinations acted as specificity switches in lambda Cro, though variant proteins displayed reduced binding specificity for their predicted target DNA sites. Two crystal structures of a lambda Cro variant are presented in Chapter 4, which provide insight into lambda Cro dimer flexibility. Additionally, a co-crystal structure of N15 Cro bound to consensus site DNA was determined which contains two coding residue pairs at the binding interface (Chapter 5), and a crystal structure of Xfasa1 Cro that enables future investigations into Cro functional evolution (Chapter 6). Although there are several caveats, the data are consistent with a model in which Cro proteins may indeed have evolved new binding specificities in part through simple mutations at their binding interfaces that follow a simple set of evolutionarily conserved "coding" rules. The structural and functional diversity of Cro proteins provides an exciting venue for future research into their evolution.

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No description available.

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