ETD Search Results: instcode:osu

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43 matches in the database. These are records: 1 - 30.

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1. An, Deokkeun. Improving the Local Distance Scale from Empirically Calibrated Stellar Isochrones.

Degree: PhD, Astronomy, 2008, Ohio State University

► Many outstanding problems concerning the formation and evolution of the Galaxy require… (more)

▼ Many outstanding problems concerning the formation and evolution of the Galaxy require accurate distances, but currently available photometric parallax relations for main-sequence (MS) stars often have anunacceptable accuracy of > ~20%. To overcome this, a method for empirically calibrating theoretical color-temperature relations was developed, with emphasis given to the critical assessment of the accuracy of the MS-fitting technique in the Johnson-Cousins-2MASS filter system. It is demonstrated that isochrones with empirical corrections accurately match the shape of the MS for nearby well-studied open clusters and provide internally consistent distances in several color indices. The resulting error in distance is estimated to be ~2% when there exists a good metallicity estimate. The distance to the Pleiades is in excellent agreement with several geometric distance measurements. Furthermore, the Cepheid period-luminosity (P-L) relation derived from Milky Way open clusters yields a distance to the maser-host galaxy NGC~4258 that agrees with the geometric measurement. These results suggest that a self-consistent local distance scale, estimated from trigonometric parallaxes, MS-fitting method, and Cepheid P-L relations, is now within reach. Photometric parallax relations in the Sloan Digital Sky Survey (SDSS) griz system are also presented to exploit the full capabilities of the SDSS imaging survey. For this purpose, SDSS imaging data for 17 globular and 3 open clusters are reduced with the DAOPHOT/ALLFRAME suite of programs. Theoretical isochrones are tested over a wide range of metallicity using the photometry and fiducial sequences for these clusters. It is demonstrated that the models are in satisfactory agreement with the data for [Fe/H] < -0.5, given the current precision of the cluster distance and metallicity estimates. However, models deviate from the data at the bottom of MS for solar and super-solar metallicity clusters. Empirical corrections to theoretical color-temperature are introduced. Finally, distances and ages of several globular clusters are derived with various color indices in griz, which are in good agreement with those in the literature from the Johnson-Cousins system. The calibrated isochrones are useful resource in the SDSS imaging survey, to study the properties of stars in the Galaxy, as well as in the future imaging surveys. Advisors/Committee Members: Terndrup, Donald M.

Subjects: Astronomy

Keywords: distance scale; stellar evolution; open clusters and associations; globular clusters

2. Andronov, Nikolay I. Evolution of close binary stars with application to cataclysmic variables and Blue Stragglers.

Degree: PhD, Astronomy, 2005, Ohio State University

► This work is dedicated to the study of the evolution of CVs… (more)

▼ This work is dedicated to the study of the evolution of CVs and mergers of close binaries. In contrast to previous studies, this work uses modern empirical formulae for angular momentum loss by magnetized stellar winds. Two important differences with previous prescriptions include the saturation of angular momentum loss rate for fast rotators, and the existence of angular momentum loss in low mass, fully convective stars. Changes in the treatment of angular momentum loss rate have a dramatic effect on the understanding of the evolution of CVs. The timescale for angular momentum loss (J̇) above the fully convective boundary is ∼2 orders of magnitude longer than inferred from the older model, and the observed angular momentum loss properties show no evidence for a change in a behavior at the fully convective boundary. This provides evidence against the hypothesis that the period gap is caused by an abrupt change in the angular momentum loss law when secondary becomes fully convective and implies that the timescale for CV evolution is much longer than was thought, comparable to a Hubble time. It is demonstrated that when evolved secondaries are included, a spread in the secondary mass-orbital period plane comparable to that seen in the data is produced for either the saturated prescription for magnetic braking or the unsaturated model commonly used for CVs. It is argued that in order to explain this spread a considerable fraction of all CVs should have evolved stars as the secondaries. The predictions of my models are compared with diagnostics of the mass accretion rate in CVs and it is found that results are intermediate between the saturated and the older braking prescription. Taken together these suggest that either the angular momentum loss rate may be higher in CV secondaries than in single stars of the same rotation period, or that accretion happens in duty cycles. Possible origins of the Period Gap are discussed. It is demonstrated that main-sequence mergers can account for the observed number of single blue stragglers in M67. Applied to the blue straggler population as a whole, this implies that such mergers are responsible for about one quarter of the population of halo blue metal poor stars, and at least one third of the blue stragglers in open clusters for systems older than 1 Gyr. The observed trends as a function of age are consistent with a saturated angular momentum loss rate for rapidly rotating tidally synchronized systems. The predicted number of blue stragglers from main sequence mergers alone is comparable to the number observed in globular clusters. A population of subturnoff mergers of order 3-4% of the upper main sequence population is also predicted for stars older than 4 Gyr, which is roughly comparable to the small population of highly Li-depleted halo dwarfs. Advisors/Committee Members: Pinsonneault, Marc H.

Subjects: Physics, Astronomy and Astrophysics

Keywords: evolution of stars; close binaries; angular momentum loss

3. AN, JIN HYEOK. Astrophysics from binary-lens microlensing.

Degree: PhD, Astronomy, 2002, Ohio State University

► Microlensing events, especially ones due to a lens composed of a binary… (more)

▼ Microlensing events, especially ones due to a lens composed of a binary system can provide new channels to approach some of old questions in astronomy. Here, by modeling lightcurves of three binary-lens microlensing events observed by PLANET, I illustrate specific applications of binary-lens microlensing to real astrophysical problems. The lightcurve of a prototypical caustics-crossing binary-lens microlensing event OGLE-1999-BUL-23, which has been especially densely covered by PLANET during its second caustic crossing, enables me to measure the linear limb-darkening coefficients of the source star in I and V bands. The results are more or less consistent with theoretical predictions based on stellar atmosphere models, although the nonlinearity of the actual stellar surface brightness profile may have complicated the interpretation, especially for I band. Next, I find that the model for the lightcurve of EROS BLG-2000-5, another caustics-crossing binary-lens microlensing event, but exhibiting an unusually long second caustic crossing as well as a very prominent third peak due to a close approach to a cusp, requires incorporation of the microlens parallax and the binary orbital motion. Its projected Einstein radius is derived from the measured microlens parallax, and its angular Einstein radius is inferred from the finite source effect on the lightcurve, combined with an estimate of the source angular size given by the source position on the color-magnitude diagram. The lens mass is found by combining the above two quantities. This event marks the first case that the parallax effects are detected for a caustic-crossing event and the first time that the lens mass degeneracy has been broken. The analysis of the lightcurve of MACHO 97-BLG-47, an almost normal event with a well-covered short-duration anomaly near the peak, shows that it is caused by an extreme-separation binary-lens. Although lightcurve anomalies that are similar to what was observed for MACHO 97-BLG-47 may result from either a planet around the lens or an extreme-separation binary, this result demonstrates that the two classes of events can be distinguished in practice. Advisors/Committee Members: GOULD, ANDREW P.

Subjects: Physics, Astronomy and Astrophysics

Keywords: gravitational microlensing; binary stars: general; stars: fundamental parameters

4. Araya Salvo, Claudia Lorena. Discovery of an Active Supermassive Black Hole in the Bulge-less Galaxy NGC 4561.

Degree: MS, Astronomy, 2012, Ohio State University

► We present XMM-Newton observations of the Chandra-detected nuclear X-ray source in NGC… (more)

Subjects: Astronomy

5. Assef, Roberto Jose. Properties of Active Galactic Nuclei and Galaxies: Spectral Energy Distributions, Luminosity Functions and Black Hole Masses.

Degree: PhD, Astronomy, 2010, Ohio State University

► We present a study on the properties of galaxies and active galactic… (more)

▼ We present a study on the properties of galaxies and active galactic nuclei (AGNs), and of their evolution through cosmic time. We start by deriving an optimal basis of low resolution empirical spectral energy distribution (SED) templates for galaxies from 0.2 to 10 μm using observations of the NOAO Deep-Wide Field Survey (NDWFS) Boötes field. We use these templates to estimate photometric redshifts and K-corrections and to study the luminosity function of galaxies as a function of galaxy type and its evolution with redshift. We then extend the set of SED templates to also include AGNs. The wavelength range of these templates is expanded to 0.03-30 μm range by adding GALEX FUV and NUV, and MIPS 24μm observations of the NDWFS Boötes field. We use these templates to estimate photometric redshifts for AGNs and to study biases in mid-IR AGN color selection techniques. We also predict the color distribution of objects in the WISE mission and design an AGN color selection criterion for it. We also present a study of the J-band luminosity function of AGNs from redshift 0 to 6. Our sample is composed of a combination of mid-IR and X-ray selected objects, which avoids the typical biases of optically selected samples. We model the luminosity function by a double power-law and find that its evolution cannot be described by either pure luminosity or pure density evolution, but must be a combination of both. Finally, we present a study of possible biases in AGN black hole (BH) mass estimates based on the CIV, Hα and Hβ broad emission lines using a sample of high redshift lensed quasars from the CASTLES project with observed-frame ultraviolet and near-infrared spectra. We find that that the residuals between CIV and Balmer line mass estimates are strongly correlated with the ratio of the UV and optical continuum luminosities, and that removing this dependency reduces the scatter between the UV and optical based BH mass estimates by a factor of approximately 2. Advisors/Committee Members: Kochanek, Christopher.

Subjects: Astronomy; Astrophysics

6. Atlee, David W. A Multiwavelength Comparison of the Growth of Supermassive Black Holes and Their Hosts in Galaxy Clusters.

Degree: PhD, Astronomy, 2011, Ohio State University

► I present the results of a mid-infrared (MIR) survey of X-ray point… (more)

▼ I present the results of a mid-infrared (MIR) survey of X-ray point sources in 8 low-z galaxy clusters. I combine visible wavelength observations with MIR data from the Spitzer Space Telescope to construct spectral energy distributions (SEDs). These SEDs form the basis of all the results presented here. From SEDs fit to the photometry, I measure galaxy stellar masses and star formation rates (SFRs), and I identify AGN based on the observed shapes of the SEDs. I also estimate the expected X-ray luminosities of the host galaxies of X-ray point sources based on their measured stellar masses and SFRs, and I identify sources whose observed X-ray luminosities show a significant excess as AGN. The two techniques return very different samples, and only 8 of the 44 identified AGN fall in both samples. The host galaxies of the two AGN samples differ significantly in their specific SFRs: the hosts of IR AGN have much larger sSFR than the X-ray AGN hosts. However, the AGN samples show similar distributions of SFRs and have indistinguishable SFR-accretion relations. This suggests that the difference between the IR and X-ray AGN is driven by the gas fraction in the host galaxies, and the IR AGN would be observed as X-ray AGN if the host galaxy did not introduce any absorption. The AGN show no significant bias in R/R200 to the positions of cluster galaxies as a whole. This distinguishes them from star forming galaxies (SFGs), which show a strong preference to be located away from the cluster center. A partial correlation analysis shows that this trend is more closely related to R/R200 than to projected galaxy density, which suggests that the SFR-density relation in clusters is driven by gas processes rather than by interactions between individual galaxies. The radial dependence of the average SFR is consistent with expectations from gas starvation within large observational uncertainties, and it is at least partially driven by changes in the SFRs of individual galaxies. This is indicated both by variations in the average sSFR among SFGs with R/R200 and by marginal variations in the break of the TIR luminosity function of cluster SFGs as a function of R/R200. These variations in the population of SFGs suggests that the transition timescale is ~400 Myr, which is intermediate between the timescales expected for ram pressure stripping and gas starvation. The observations suggest that gas starvation plays a greater role than ram pressure stripping, but further work is needed. One possible avenue for future work is to examine the evolution in SFRs of cluster galaxies as a function of redshift. This probes the timescale for clusters to end star formation in galaxies as they fall in from the field. Advisors/Committee Members: Martini, Louis.

Subjects: Astronomy

Keywords: AGN clusters galaxy evolution

7. Bentz, Misty C. Black hole scaling relationships: new results from reverberation mapping and Hubble Space Telescope imaging.

Degree: PhD, Astronomy, 2007, Ohio State University

► We investigate the results of reverberation-mapping mass measurements and two-dimensional (2-D) decompositions… (more)

▼ We investigate the results of reverberation-mapping mass measurements and two-dimensional (2-D) decompositions of high-resolution host galaxy images in the context of black hole scaling relationships. We present new monitoring data leading to an improved black hole mass measurements for the nearby Seyfert galaxy NGC 4151. We also present new monitoring data for the well-studied NGC 5548, which show the active galactic nucleus (AGN) in the lowest luminosity state during a monitoring campaign. We show that the mass derived from this low state is consistent with previous mass measurements, and that the virial relationship previously discovered between the width of the broad lines and their time lags relative to the continuum flux still holds. We also present complete, 2-D galaxy decompositions for 29 of the 36 objects in the reverberation-mapped sample. We create PSF-subtracted images of the host galaxies and measure the starlight contribution to the luminosity measurements from the original monitoring programs. Accounting for this contribution, we revisit the radius – luminosity relationship for AGNs and find a reduced scatter and a slope of approximately 0.5 that holds over 5 decades in luminosity. This slope is consistent with the naive expectation that all AGNs are simply scaled models of each other. Finally, we use the galaxy model parameters to investigate several black hole mass scaling relationships with host galaxy properties, namely the black hole mass – bulge luminosity relationship, the black hole mass – bulge mass relationship, and the black hole mass – Sérsic index relationship. We find tight correlations for the black hole mass – bulge luminosity and black hole mass – bulge mass relationships, but these results only marginally agree with previous studies. Rather, they point to an increased black hole mass fraction at lower bulge luminosities and masses than was previously seen. Additionally, we find no evidence for the black hole mass – Sérsic index relationship in this sample of objects. We discuss several differences between the methods employed by various studies and how these may lead to the observed discrepancies in the results. Advisors/Committee Members: Peterson, Bradley M.

Subjects: Physics, Astronomy and Astrophysics

8. Bird, Jonathan C. The Formation and Evolution of Disk Galaxies.

Degree: PhD, Astronomy, 2012, Ohio State University

► Current and next generation surveys of the Milky Way promise to revolutionize… (more)

▼ Current and next generation surveys of the Milky Way promise to revolutionize our observational perspective of the Galaxy. My dissertation uses a suite of N-body and SPH simulations of disk galaxies to make testable predictions of the assembly history of the Milky Way and identify observational probes that take advantage of the forthcoming data. APOGEE, an infrared survey of the Galaxy and a component of the SDSS-III, will measure the distance, radial velocity, and multi-element chemistry of 10^5 stars located throughout the Galaxy, making it particularly well suited for comparison with simulations. We first use a fuel-consumption argument to constrain the integrated luminosity of the TP-AGB phase; the energy release in this phase is a major uncertainty in stellar population synthesis models. Our initial numerical investigation explores how the minor mergers expected in Lambda-CDM and inherent properties of stellar disks affect the dynamics of stellar radial migration- an essential ingredient in understanding the evolution of the Milky Way and disk galaxies in general. We discover that the resonances and mechanisms responsible for migration are different in isolated and satellite-bombarded galaxies, resulting in distinct migration patterns and potential observational signatures of accretion events. Continuing our development of tools to describe the chemo-dynamics of the disk, we construct statistics to measure overdensities and characterize outliers in the distance, radial velocity projection of phase space. I discuss mock APOGEE observations of our numerical simulations and demonstrate that our statistics can begin to discriminate between significant galaxy formation mechanisms given the data available in the near term. Finally, we use a state of the art cosmological simulation to describe the evolution of mono-age stellar populations and their eventual assembly into a galaxy resembling the Milky Way. Galaxy formation theory faces the exciting challenge of an unprecedented level of statistical scrutiny: imminent and ongoing surveys such as SEGUE, RAVE, APOGEE, LAMOST, and HERMES offer an extraordinary opportunity to unravel the formation history of the Milky Way. Advisors/Committee Members: Weinberg, David.

Subjects: Astronomy; Astrophysics

Keywords: Galaxy formation, astrophysics, near-field cosmology

9. Burke, Christopher J. Survey for transiting extrasolar planets in stellar systems: stellar and planetary content of the Open Cluster NGC 1245.

Degree: PhD, Astronomy, 2005, Ohio State University

► An investigation into the stellar and planetary content of the open cluster… (more)

10. Chaname, Julio. Topics of galactic structure and stellar and chemical evolution.

Degree: PhD, Astronomy, 2005, Ohio State University

► In this thesis I explore current problems of Galactic astronomy by following… (more)

▼ In this thesis I explore current problems of Galactic astronomy by following two distinct but complementary approaches: the kinematic and photometric properties of local stellar populations, and the theory of stellar evolution. Under the first approach, I construct the largest available catalog of genuine wide binaries (a > 100 AU) and, using the relative positions of both components on a reduced proper-motion diagram, I cleanly classify them as belonging to either the disk or the halo of the Galaxy. These samples, drawn from the Revised New Luyten Two-Tenths catalog, are complete to separations of 500 and 900 arcsec, corresponding to about 0.1 and 1 parsec, respectively. At wide separations, both distributions are well described by power laws that have, within the uncertainties, identical exponents. The fact that these distributions have similar slopes and normalizations, despite the radically different Galactic environments to which they belong today, argues for similarity of the star-formation conditions of the two populations. The fact that the halo binaries obey a single power law out to about 1 parsec permits strong constraints on halo dark-matter candidates. Using Monte Carlo simulations, we exclude a halo fully composed of MAssive Compact Halo Objects (MACHOs) more massive than 43 solar masses at 95 percent confidence. I outline the prospects for using the Sloan Digital Sky Survey in the assembly of a catalog of halo wide binaries which, by improving the statistics at large separations, will enable exploration of MACHO masses in the astrophysically important regime of heavy stellar remnants. Finally, taking advantage of the identification of faint companions of Hipparcos stars, I construct a catalog of 424 intrinsically dim (i.e., low-mass) field stars with accurate (better than 3-sigma) parallaxes. Under the approach of stellar evolution, I study the long-standing problem of abundance anomalies in red giants, concentrating in non-standard mixing processes induced by stellar rotation. Unlike most previous work, I focus on the simultaneous reproduction of the CNO abundances in both Population I and Population II giants using the same physics and models. This novel approach led to a powerful new insight on one of the most difficult problems of astrophysics: the interplay between convection and rotation in stellar envelopes. Advisors/Committee Members: Gould, Andrew P.

Subjects: Physics, Astronomy and Astrophysics

Keywords: binaries; stars; halo; proper-motion; extra mixing; RGB; ï¬rst

11. Chen, Guo-Xin. Relativistic close coupling calculations for fundamental atomic processes in astrophysics.

Degree: PhD, Astronomy, 2004, Ohio State University

► The study of fundamental atomic processes has long been one of the… (more)

▼ The study of fundamental atomic processes has long been one of the most active astrophysical fields. First, we carry out elaborate relativistic atomic calculations of radiative and collisional processes using the Breit-Pauli R-matrix method with one-electron relativistic terms included. We extensively studied low-energy electron impact excitation (EIE) of Fe XVII with emphasis on relativistic and resonance effects. We showed that all N-shell levels give rise to Rydberg resonant states dipping right to M-shell thresholds. These new findings significantly affect the collision strengths for the primary X-ray and EUV transitions among the first 37 levels. We also pointed out the importance of some M2 and E3 multipole transitions in Fe XVII. Accurate X-ray line ratios from strong X-ray lines in Fe XVII were computed and compared with observations. Based on this study and the study of different electron distribution functions in plasmas via collisional-radiative models, two long-standing astrophysical problems of X-ray line intensity ratios 3C/3D and 3s/3d are resolved. The strong energy dependence due to resonances in cross sections was demonstrated. These results are useful for plasma diagnostics in X-ray astronomy. From applications of our Fe VI atomic calculations to planetary nebulae, we developed a method to constrain simultaneously a set of physical conditions. Fluorescent excitation of spectral lines was demonstrated as a function of temperature-luminosity and the distance of the emitting region from the central stars of planetary nebulae. Fluorescence should also be important in the determination of element abundances. We suggested that the method could be generally applied to determine or constrain the luminosity and the region of spectral emission in other luminous sources. We present relativistic close-coupling calculations for unified radiative (RR) and dielectronic recombination (DR), photoionzation and excitation in C IV and Fe XVII. K- and L-shell resonant X-ray absorptions due to O ions and Fe XVI were computed and compared with the Chandra spectra of the Seyfert 1 galaxy MCG—6-30-15. We developed an efficient STGFR code for calculating radiation damping and DR. Next, as the second part of this dissertation, we developed a full Breit-Pauli R-matrix code. We include all the two-electron fine-structure terms, the non-fine-structure spin-spin contact interaction and the two-electron Darwin term. Advisors/Committee Members: Pradhan, Anil K.

Keywords: collision strengths; RELATIVISTIC; electron; ct al; resonance; collision; Fe

12. Delahaye, Franck. From accurate atomic data to elaborate stellar modeling: Structure and collisional data, opacities, radiative accelerations.

Degree: PhD, Astronomy, 2005, Ohio State University

► The new requirements for accuracy and completeness in atomic data from astronomers… (more)

▼ The new requirements for accuracy and completeness in atomic data from astronomers demand more challenging calculations. Current problems require the relaxation of approximations and detailed studies of different effects like relativistic effects. We carry out relativistic atomic calculations using the Breit-Pauli R-matrix method to generate radiative and collisional data for ions of astrophysical interest. Electron impact excitation of He-like ions have been calculated including relativistic effects, radiation damping and other effects. The comparison with previous works shows differences of up to 30% in the effective collision strengths for the z-line. This line with 3 other transitions between the complexes n=1 and n=2 constitute an important tool for plasma diagnostics and such differences will have strong consequences in the analysis of X-Ray spectra of astronomical objects. We present the relativistic calculation of Kα resonances for oxygen ions that are responsible for X-Ray absorption features observed in the spectrum of AGNs. Resonance oscillator strengths have been computed and are in good agreement with the recent experimental and theoretical study of Kα photoionization of O II. These data should allow a more complete analysis of X-Ray spectra from AGNs and refine the general picture of such complex objects. We report the first large relativistic calculation of the photoionization cross section of Fe II. The detailed fine structure in the present work agrees well with the experimental results from Kjeldsen et al. (2002) and represents an improvement over the previous non-relativistic results. These data should be useful to the theoretical template of Fe II emissions crucial in the analysis of the UV/O/IR spectrum of AGNs. The new OP opacities are presented, outlining the importance of the inner-shell transitions at high temperature-high density regimes. This new set of data is used to determine constraints on the solar composition and to shed some light on the 'Solar Convection Problem'. While the discrepancies between the two sources (OP and OPAL) are minor for the Rosseland mean opacities, they affect more severely the radiative accelerations. The comparison between the two sets of accelerations outlines their sensitivity to details in monochromatic opacities. The consequences for stellar models are discussed. Advisors/Committee Members: PRADHAN, Anil K.

Keywords: Atomic data: relativistic calculations; X-Ray diagnostic; opacity; Stellar modelling; solar composition; star: micro-diffusion; star: radiative accelerations

13. Denney, Kelly D. Black Hole Masses in Active Galactic Nuclei.

Degree: PhD, Astronomy, 2010, Ohio State University

► We present the complete results from two, high sampling-rate, multi-month, spectrophotometric reverberation… (more)

▼ We present the complete results from two, high sampling-rate, multi-month, spectrophotometric reverberation mapping campaigns undertaken to obtain either new or improved Hβ reverberation lag measurements for several relatively low-luminosity active galactic nuclei (AGNs). We have reliably measured the time delay between variations in the continuum and Hβ emission line in seven local Seyfert 1 galaxies. These measurements are used to calculate the mass of the supermassive black hole at the center of each of these AGNs. We place our results in context to the most current calibration of the broad-line region (BLR) RBLR-L relationship, where our results remove many outliers and significantly reduce the scatter at the low-luminosity end of this relationship. A detailed analysis of the data from our high sampling rate, multi-month reverberation mapping campaign in 2007 reveals that the Hβ emission region within the BLRs of several nearby AGNs exhibit a variety of kinematic behaviors. Through a velocity-resolved reverberation analysis of the broad Hβ emission-line flux variations in our sample, we reconstruct velocity-resolved kinematic signals for our entire sample and clearly see evidence for outflowing, infalling, and virialized BLR gas motions in NGC 3227, NGC 3516, and NGC 5548, respectively. Finally, we explore the nature of systematic errors that can arise in measurements of black hole masses from single-epoch spectra of AGNs by utilizing the many epochs available for NGC 5548 and PG1229+204 from reverberation mapping databases. In particular, we examine systematics due to AGN variability, contamination due to constant spectral components (i.e., narrow lines and host galaxy flux), data quality (i.e., signal-to-noise ratio, S/N), and blending of spectral features. We investigate the effect that each of these systematics has on the precision and accuracy of single-epoch masses calculated from two commonly-used line-width measures by comparing these results to recent reverberation mapping studies. We then present an error budget which summarizes the minimum observable uncertainties as well as the amount of additional scatter and/or systematic offset that can be expected from the individual sources of error investigated. Advisors/Committee Members: Peterson, Bradley M.

Subjects: Astronomy; Astrophysics

Keywords: Astronomy; supermassive black holes; active galactic nuclei; AGN; black hole masses; Seyfert galaxies

14. Dong, Subo. Astrophysical Applications of Gravitational Microlensing.

Degree: PhD, Astronomy, 2009, Ohio State University

► In this thesis, I present several astrophysical applications of Galactic and cosmological… (more)

▼ In this thesis, I present several astrophysical applications of Galactic and cosmological microlensing.The first few topics are on searching and characterizing extrasolar planets by means of high-magnification microlensing events. The detection efficiency analysis of Amax ~ 3000 event OGLE-2004-BLG-343 is presented. Due to human error, intensive monitoring did not begin until 43 minutes after peak, at which point the magnification had fallen to Amax ~ 1200. It is shown that, had a similar event been well sampled over the peak, it would have been sensitive to almost all Neptune-mass planets over a factor of 5 in projected separation and even would have had some sensitivity to Earth-mass planets. New algorithms optimized for fast evaluation of binary-lens models with finite-sources effects have been developed. These algorithms have enabled efficient and thorough parameter-space searches in modeling planetary high-magnification events. The detection of the cool, Jovian-mass planet MOA-2007-BLG-400Lb, discovered from an Amax = 628 event with severe finite source effects, is reported. Detailed analysis yields a fairly precise planet/star mass ratio of q = (2.5 ± 0.4) x 10-3, while the planet/star projected separation is subject to a strong close/wide degeneracy. Photometric and astrometric measurements from Hubble Space Telescope, as well as constraints from higher order effects extracted from the ground-based light curve (microlens parallax, planetary orbital motion and finite-source effects) are used to constrain the nature of planetary event OGLE-2005-BLG-071Lb. Our primary analysis leads to the conclusion that the host is an M = 0.46 ± 0.04 MSun M dwarf and that the planet has mass Mp = (3.8 ± 0.4) MJupiter, which is likely to be the most massive planet yet discovered that is hosted by an M dwarf. Next a spaced-based microlens parallax is determined for the first time using Spitzer and ground-based observations for binary-lens event OGLE-2005-SMC-001. The parallax measurement yields a projected velocity about 239 km/s, the typical value expected for halo lenses, but an order of magnitude smaller than would be expected for lenses lying in the Small Magellanic Cloud (SMC) itself. Finally, I propose using quasar microlensing to probe Mg II and other absorption "cloudlets" with sizes ~ 10-4.0 - 10-2.0 pc in the intergalactic medium. I show that significant spectral variability on timescales of months to years can be induced by such small-scale absorption "cloudlets" toward a microlensed quasar. With numerical simulations, I demonstrate the feasibility of applying this method to Q2237+0305, and I show that high-resolution spectra of this quasar in the near future would provide a clear test of the existence of such metal-line absorbing "cloudlets". Advisors/Committee Members: Gould, Andrew.

Subjects: Astronomy

15. Eastman, Jason David. DEMONEX: The DEdicated Monitor of EXotransits.

Degree: PhD, Astronomy, 2011, Ohio State University

► Transiting planets are extraordinarily useful laboratories to study the formation and evolution… (more)

▼ Transiting planets are extraordinarily useful laboratories to study the formation and evolution of planets as a whole. In order to capitalize on this potential, we built DEMONEX, the DEdicated MONitor of EXotransits, a low-cost, 0.5 meter, robotic telescope, mostly from commercially-available parts. The primary goal of DEMONEX is to monitor bright stars hosting transiting planets in order to provide a homogeneous data set for all known transiting systems visible from its location at Winer Observatory in Sonoita, Arizona. The main advantage of DEMONEX is that it can be used every night for transit follow-up. With over 60 known transiting planets visible from Winer Observatory, more than 90% of its time can be spent observing transits. In chapter 1, we describe the hardware, scheduling, observing, data reduction software, and we present some results from the first three years of operation. One of the most powerful tools that observing multiple transits gives us is the ability to observe Transit Timing Variations (TTVs) – slight variations in the otherwise perfectly periodic times of transits due to, among other things, other planets in the system. However, the times that many people report are ambigious at a level than threatens the utility of the technique. In chapter 2, we detail the steps necessary to accurately convert the time as measured on Earth, the JD_UTC, to an astrophysically-meaningful time, the BJD_TDB, with a precision that far surpasses the practical limit for TTVs. In order to analyze the vast amounts of data that DEMONEX has collected, in chapter 3 we discuss our analysis software, EXOFAST. It is a fast, robust suite of routines written in IDL designed to fit exoplanetary transits and radial velocity simultaneously and characterize the parameter uncertainties of and covariances of exoplanetary systems with a Markov Chain Monte Carlo method. We take particular care to make it robust, fast, and self-consistent. We outline ways in which the code can easily be extended to include additional effects or generalized for the characterization of any data set – including non-planetary data sets. Of particular interest, we discuss the effects of eccentricity bias and demonstrate the effectiveness of our new strategy to mitigate it, derive a method to analtyically fit the linear and quadratic limb darkening coefficients of a planetary transit, and explain how we achieved improved robustness and over a factor of 100 improvement in the run time of the transit model calculation. Our source code, along with easy-to-use online tools for both the timing code and EXOFAST can be found online. Advisors/Committee Members: Gaudi, B. Scott.

Subjects: Astronomy

Keywords: exoplanets; transits; timing; instrumentation; robotic telescope; markov chain monte carlo; bayesian

16. Fields, Dale. Absorption-line measurements of AGN outflows.

Degree: PhD, Astronomy, 2006, Ohio State University

► Investigations into the elemental abundances in two nearby active galaxies, the narrow-line… (more)

▼ Investigations into the elemental abundances in two nearby active galaxies, the narrow-line Seyfert 1 (NLS1) Markarian 1044 and the Seyfert 1 Markarian 279, are reported. Spectra from three space-based observatories HST, FUSE, and CHANDRA, are used to measure absorption lines in material outflowing from the nucleus. I make multi-wavelength comparisons to better convert the ionic column densities into elemental column densities which are then used to determine abundances (metallicities). NLS1 galaxies are known to have extreme values of a number of properties compared to active galactic nuclei (AGNs) as a class. In particular, emission-line studies have suggested that NLS1s are unusually metal-rich compared to broad-line AGNs of comparable luminosity. To test these suggestions I perform absorption-line studies on the NLS1 Markarian 1044. I use lines of HI, CIV, NV, and OVI to properly make the photoionization correction through the software Cloudy and determine abundances of Carbon, Nitrogen and Oxygen. I find two results. The first is that Markarian 1044 has a bulk metallicity greater than five times solar. The second is that the N/C ratio in Markarian 1044 is consistent with a solar mixture. This is in direct contradiction of extrapolations from local HII regions which state N/C should scale with bulk metallicity. This implies a different enrichment history in Markarian 1044 than in the Galactic disk. I also report discovery of three new low-redshift Ly-alpha forest lines with log N HI>12.77 in the spectrum of Markarian 1044. This number is consistent with the 2.6 expected Ly-alpha forest lines in the path length to Markarian 1044. I also investigate the CHANDRA X-ray spectrum of Markarian 279, a broad-line Seyfert 1. I use a new code, PHASE, to self-consistently model the entire absorption spectrum simultaneously. Using solely the X-ray spectrum I am able to determine the physical parameters of this absorber to a degree only slightly poorer than in the multi-wavelength study of Markarian 1044. I find consistency with solar abundance in this Seyfert 1. Advisors/Committee Members: Mathur, Smita.

Subjects: Physics, Astronomy and Astrophysics

Keywords: Narrow-line Seyfert 1; Absorption lines; Abundances

17. Frank, Stephan. OVI Absorbers in SDSS Spectra.

Degree: PhD, Astronomy, 2008, Ohio State University

► We conducted a systematic search for signatures of the Intergalactic Medium in… (more)

▼ We conducted a systematic search for signatures of the Intergalactic Medium in Quasar spectra of the Sloan Digital Sky Survey, focusing on intervening absorbers via detection of their OVI doublet. We present a search algorithm, and criteria for distinguishing candidates from spurious Lyman lines. In addition, we compare our findings with simulations of the Lyα forest to estimate the detectability of OVI over various redshift intervals. We obtain a sample of 1866 candidates with equivalent widths > 0.05 A in 855 AGN spectra (out of 3702 objects with redshifts in the range for OVI detection). We divide the sample into 3 groups according to the likelihood of being real and potential for follow-up observations. The best group is comprised of 145 candidates, 69 of these reside at a velocity separation > 5000 km/s from the QSO, and can be classified tentatively as intervening absorbers. Most of these have not been picked up by earlier absorption line detection algorithms. This sample increases the number of OVI absorbers at redshifts beyond 2.7 substantially. We propose to obtain observations of some candidates with high signal-to-noise and resolution to better constrain the physical state of the absorbers.We then focus on 387 sightlines with a S/N > 5.0, allowing for the detections above a rest-frame EW > 0.19 A for the 1032 A component. Accounting for random interlopers, we derive for the first time a lower limit for the redshift number density for z > 2.8. With extensive Monte Carlo simulations we quantify losses of absorbers due to blending with Lyα forest lines, and estimate the success rate of retrieving individual candidates. This allows us to derive the ‘incompleteness corrected’ redshift number density. We place a secure lower limit for the contribution of OVI to the mass density at the redshifts probed here. We show that the strong lines account for 65% of the mass in the OVI absorbers; weak absorbers, dominant in line number density, do not contribute significantly. Making conservative assumptions about the ionisation fraction, we derive the mean metallicity of the gas, which is in good agreement with other studies. These results demonstrate that large spectroscopic datasets as SDSS play an important role in QSO absorption line studies, despite their relatively low resolution. Lastly, we performed a stacking analysis whereby we shift individual spectra to the rest-frame of the absorber, and derive a mean spectrum. Besides further validating the reality of candidates, we use stacked spectra for a variety of purposes. First, we judge effects of additional cuts like a minimal strength for CIV absorption, and produce cleaner subsamples, increasing the strength of proposals for high-resolution studies. Secondly, the stack itself contains information about the gas probed in our search. We have begun to measure absorption features for an OVI+CIV selected subsample, and compared them with multiple transitions found in a CIV-only selected sample. One of the first results is that we probe gas with large OVI column densities lacking many of the lower ionisation lines frequently seen in CIV-selected systems. Advisors/Committee Members: Mathur, Smita.

Subjects: Astronomy; Astrophysics

Keywords: IGM; QSO Absorption lines

18. Ghosh, Himel. A Search for the Smallest Supermassive Black Holes.

Degree: PhD, Astronomy, 2009, Ohio State University

► Relations between supermassive black holes (SMBHs) and their hostgalaxies are now well… (more)

▼ Relations between supermassive black holes (SMBHs) and their hostgalaxies are now well known, but several questions remain: Do all galaxies harbor SMBHs? Do correlations between BH mass and host galaxy properties extend to lower mass BHs and all galaxy types? Is the galactic bulge or the dark matter halo the defining component for the nuclear BH? Answering these questions requires a study of low mass SMBHs, in particular those that reside in the latest-type spiral galaxies. While the presence of an active galactic nucleus (AGN) provides certain proof of the existence of an SMBH, galaxies that are not previously known to host AGNs may nevertheless have SMBHs at their centers. In other words, a galaxy may appear quiescent when in reality there is an accreting SMBH, if the accretion level is low enough. This thesis presents a search for such SMBHs by looking for the presence of low-level nuclear activity, as evidenced primarily by their x-ray emission, in a well-defined sample of nearby, optically quiescent spiral galaxies. This work demonstrates that traditional methods of identifying AGNs, developed over the course of studying luminous (> 1042 erg/s) AGNs, are inadequate for the population of low luminosity AGNs found in nearby galaxies, and develops the techniques that must be used instead. These techniques are then applied to an x-ray survey of nearby, face-on spiral galaxies. The survey includes new snapshot observations of 37 galaxies, which are combined with archival data for a further 18 galaxies. Where available, multi-wavelength data are used to help distinguish AGNs from other types of x-ray sources. These observations show the power of x-ray observations in detecting hidden AGNs, and also address the question of the prevalence of SMBHs in spiral galaxies that do not have bulges. This study has uncovered 14 previously unknown AGNs and strong AGN candidates, including two in galaxies of type Sd and Sdm. If the latter are confirmed as bona fide AGNs they will be only the fourth and fifth AGNs known to exist in bulgeless galaxies. Advisors/Committee Members: Mathur, Smita.

Subjects: Astronomy; Astrophysics

Keywords: active galactic nuclei; spiral galaxies; late-type spirals

19. Jiang, Guangfei. Dark and Luminous Matter in Galaxies and Large Scale Structure.

Degree: PhD, Astronomy, 2008, Ohio State University

► In standard cosmology, both the dark matter and baryons are important constituents… (more)

Subjects: Astrophysics

Keywords: lya; proximity effect; baryon fraction; optical observables

20. Kassin, Susan Alice Joan. Dark and luminous matter in bright spiral galaxies.

Degree: PhD, Astronomy, 2004, Ohio State University

► I present photometrically calibrated images and surface photometry in the BVRJH and… (more)

▼ I present photometrically calibrated images and surface photometry in the BVRJH and K-bands of 26, and in the g, r, and K-bands of 5 nearby bright (B<12.5 mag) spiral galaxies with inclinations between 30-65 degrees spanning the Hubble Sequence from Sa to Scd. Data are from The Ohio State University Bright Spiral Galaxy Survey, the Two Micron All Sky Survey, and the Sloan Digital Sky Survey Second Data Release. Radial surface brightness profiles are extracted, and integrated magnitudes are measured from the profiles. Axis ratios, position angles, and scale lengths are measured from the near-infrared. A 1-dimensional bulge/disk decomposition is performed on galaxies with a non-negligable bulge component. Radial stellar mass distributions are estimated by applying color-M/L relations derived from spectrophotometric spiral galaxy evolution models to the photometry. When available, radial gas masses are added to the radial stellar mass distributions to produce radial baryonic mass distributions. For each galaxy, a rotation curve due to its radial baryonic mass distribution is calculated, taking into account both the bulge and disk components when necessary. All of the galaxies have high-quality rotation curves available in the literature which allows us to calculate radial dark matter distributions for each galaxy by comparison with the baryonic mass rotation curves. Most galaxies are found to have maximal stellar disks, but seven are found to be submaximal in their inner parts (inner five scale radii). The following quantities are derived to characterize the radial baryonic and dark matter content of galaxies, and are found to correlate with Hubble Type: the peak velocity of the baryonic rotation curve (V*max), the radius at which the dark matter contributes 10% to the observed rotation curve (R10), and the radius at which dark matter contributes 50%(RX). From the radial distribution of beta(r), I find that although the behavior of the dark matter distributions are qualitatively similar from galaxy to galaxy, there is systematic scatter among them to argue against a universal rotation curve. The general qualitative shape the beta(r) curves is what is expected from an exponential baryonic disk and a rotation curve that is nearly flat at large radii. Advisors/Committee Members: Pogge, Richard W.

Subjects: Physics, Astronomy and Astrophysics

Keywords: Galaxies, Rotation Curves, Dark Matter, Photometry

21. Kollmeier, Juna Ariele. The intergalactic medium: absorption, emission, disruption.

Degree: PhD, Astronomy, 2006, Ohio State University

► Two fundamental predictions of modern cosmological models are that i) galaxies form… (more)

▼ Two fundamental predictions of modern cosmological models are that i) galaxies form from small perturbations in the cosmic density field and ii) there is a tenuous medium between the galaxies that traces the underlying dark matter distribution in a relatively simple way. This thesis concerns the structure of the intergalactic medium (IGM) and its relation to galaxies. Specifically, I analyze the nature of the IGM, observable via the Lyman-alpha transition of hydrogen, as predicted from cosmological hydrodynamic simulations of a cold dark matter + dark energy universe. I first quantify the relation between galaxies and absorption in the Lyman-alpha forest on large (~10 Megaparsec) and small (~0.5 Megaparsec) scales and show that, in the absence of feedback from the galaxies themselves, observations of this relation can serve as robust tests of the inflationary cold dark matter model. I show that the strong bias of high redshift galaxies toward high density regions imprints a clear signature on the distribution of flux in the Lyman-alpha forest, and these predictions are examined as functions of galaxy baryon mass, star formation rate, and dark matter halo mass and occupation. I then investigate the potential impact of galaxies on the IGM and find that supernova-driven winds (as predicted in cosmological simulations) can substantially impact their local surroundings, particularly via heating, but that only very powerful winds can create easily detectable “holes” in the IGM. The impact of winds on the Lyman-alpha optical depth near galaxies is less dramatic than their impact on gas temperature because winds heat only a small fraction of the gas present in the turnaround regions surrounding galaxies, all of which contribute to the Lyman-alpha forest near galaxies. Finally, I combine a Monte Carlo radiative transfer code with cosmological hydrodynamic simulations to investigate the signature of fluorescent Lyman-alpha emission from large scale structure due to impinging radiation from the metagalactic ionizing background as well as local bright sources such as quasars. I compare these predictions with current observations and discuss future observing campaigns and realistic strategies for detecting fluorescence from the ambient metagalactic ionization as well as in the vicinity of bright quasars. Advisors/Committee Members: Weinberg, David Hal.

Subjects: Physics, Astronomy and Astrophysics

Keywords: Intergalactic Medium; Galaxy formation; Galaxy evolution; Quasar absorption line systems; Large scale structure

22. Lacki, Brian Cameron. Cosmic Rays in Star-Forming Galaxies.

Degree: PhD, Astronomy, 2011, Ohio State University

► Cosmic rays (CRs) are high energy particles that are found wherever in… (more)

▼ Cosmic rays (CRs) are high energy particles that are found wherever in the Universe star formation is occurring. I investigate several problems in the propagation of CRs in star-forming galaxies. By applying analytic models and numerically solving the “leaky box” differential equation, I calculate the population of primary and secondary CR protons, electrons and positrons in model star-forming galaxies and their nonthermal emission. Observations show that the synchrotron radio emission of star-forming galaxies grows linearly with the infrared emission from dust-obscured young stars; this is the FIR-radio correlation (FRC). To explain the correlation, I constructed one-zone models of galaxies over the dynamic range of the FRC. I found that the FRC is caused by conspiracies of several factors, including CR escape from galaxies, ultraviolet (UV) dust opacity, non-synchrotron cooling, and secondary electrons and positrons generated by CR protons. The conspiracies have great implications for the evolution of the FRC at high redshift, preserving it and allowing variations in the FIR-radio ratio for submillimeter galaxies. Recent gamma-ray observations of M82 and NGC 253 indicate that CR protons lose much of their energy to collisions in these galaxies’ dense gas, where they generate unstable pions that decay into gamma rays and secondary particles. The ratio of gamma-ray to radio luminosity indicates that secondary electrons mostly do not cool by synchrotron emission, supporting a conspiracy origin of the FRC. I also compare the intensities of the diffuse cosmic gamma-ray background to the X-ray and radio backgrounds. From this comparison, I find that Inverse Compton is a minority of the X-ray background, and that the radio background is probably not from starbursts. Finally, I modeled the nonthermal X-ray emission from starburst galaxies, both synchrotron from TeV electrons and Inverse Compton from GeV electrons. The synchrotron emission is enhanced by gamma-gamma pair production in the intense infrared radiation of starbursts. Synchrotron and Inverse Compton emission make up 1 - 10% of the observed diffuse hard X-ray emission observed in starburst galaxies. Advisors/Committee Members: Thompson, Todd.

Subjects: Astronomy; Astrophysics

Keywords: cosmic rays; galaxies; radio emission from galaxies; gamma rays from galaxies; cosmic radio background; cosmic gamma-ray background

23. Markowitz, Allan Henry. A study of stars exhibiting composite spectra.

Degree: PhD, Astronomy, 1969, Ohio State University

Advisors/Committee Members: Slettebak, Arne.

24. Marshall, Jennifer L. Mapping the Local Galactic Halo and An Image Motion Compensation System for the Multi-Object Double Spectrograph.

Degree: PhD, Astronomy, 2006, Ohio State University

► In the first part of this dissertation I describe the results of… (more)

▼ In the first part of this dissertation I describe the results of a photometric and spectroscopic survey of a sample of cool, metal-poor subdwarfs in the solar neighborhood. These metal-poor stars are of interest because, as members of the Galactic halo, they give clues about the history of the Galaxy and its formation mechanisms, and may enable us to study satellites of the Milky Way and the Galactic merger history. A sample of halo subdwarfs have been selected using a reduced proper motion (RPM) diagram. Accurate and precise photometric measurements of 635 stars selected in this manner allow better definition of the RPM diagram and determination of its usefulness as a selection method. Accurate spectrophotometry yields radial velocities of the candidates as well as metallicity and temperature estimates for 288 subdwarfs. Of special interest in this sample are the ten newly discovered extremely metal-poor stars, as well as four carbon-enhanced metal-poor stars. I use these new observations to search the local Galactic halo for structure due to merger remnants and moving groups; there is some evidence for both. I also discuss the metallicity distribution function of the sample and compare it to previous work on this subject. No astronomical observations of any sort are possible without appropriate, well-calibrated instrumentation with which to perform the measurements. In the second part of this dissertation, I describe the Image Motion Compensation System (IMCS) for the Multi-Object Double Spectrograph (MODS), an optical spectrograph for the Large Binocular Telescope. The system performs closed-loop image motion compensation, actively correcting for image motion in the spectrograph's focal plane caused by large scale structural bending due to gravity as well as other effects such as temperature fluctuation and mechanism flexure within the instrument. The system is currently installed in the MODS instrument and controls instrumental flexure to within specifications. I describe the initial development efforts of this system, results from the preliminary laboratory tests, and the final performance of the system as deployed in the MODS spectrograph. Advisors/Committee Members: DePoy, Darren L.

Subjects: Physics, Astronomy and Astrophysics

Keywords: Galactic Astronomy – Cool Subdwarfs; Astronomical Instrumentation

25. Mogren, Karen Nicole. Analytic Expressions for the Detectability of Exoplanets in Radial Velocity, Astrometric, and Transit Surveys.

Degree: MS, Astronomy, 2012, Ohio State University

► We derive analytic expressions for the detectability of exoplanets in radial velocity… (more)

Subjects: Astronomy; Astrophysics

Keywords: radial velocity; astrometry; transits; exoplanets; extrasolar planets; detectability

26. Morgan, Christopher Warren. Quasar Structure from Microlensing in Gravitationally Lensed Quasars.

Degree: PhD, Astronomy, 2008, Ohio State University

► I analyze microlensing in gravitationally lensed quasars to yield measurements of the… (more)

▼ I analyze microlensing in gravitationally lensed quasars to yield measurements of the structure of their continuum emission regions. I first describe our lensed quasar monitoring program and RETROCAM, the auxiliary port camera I built for the 2.4m Hiltner telescope to monitor lensed quasars. I describe the application of our Monte Carlo microlensing analysis technique to SDSS 0924+0219, a system with a highly anomalous optical flux ratio. For an inclination angle cos(i)=0.5, I find an optical scale radius log[r_s/cm] = 14.8±0.4. I extrapolate the best-fitting light curves into the future to find a roughly 45% probability that the anomalous image (D) will brighten by at least an order of magnitude during the next decade. I expand our method to make simultaneous estimates of the time delays and structure of HE1104-1805 and QJ0158-4325, two doubly-imaged quasars with microlensing and intrinsic variability on comparable time scales. For HE1104-1805, I find a time delay of Delta t_{AB} = 162±6 days and estimate a scale radius of log[r_s/cm] = 15.7±0.5 at 200 nm in the rest frame. I am unable to measure a time delay for QJ0158-4325, but the scale radius is log[r_s/cm] = 14.9±0.3 at 300 nm in the rest frame. I then apply our Monte Carlo microlensing analysis technique to the optical light curves of 11 lensed quasar systems to show that quasar accretion disk sizes at 250 nm are strongly correlated with black hole mass. The resulting scaling relation is consistent with the expectation from thin disk theory, but it implies that black holes radiate with relatively low efficiency. These sizes are also larger, by a factor of approximately 3, than the size needed to produce the observed 800 nm quasar flux by thermal radiation from a thin disk with the same temperature profile. Finally, I analyze the microlensing of the X-ray and optical emission of the lensed quasar PG 1115+080. I find that the size of the X-ray emission region is approximately 1.3 dex smaller than that of the optical emission, and I find a weak trend supporting models with low stellar mass fractions near the lensed images. Advisors/Committee Members: Kochanek, Christopher.

Subjects: Astronomy; Astrophysics

Keywords: accretion, accretion disks; dark matter; gravitational lensing; quasars: general

27. Nataf, David M. The Galactic Bulge Stellar Population.

Degree: PhD, Astronomy, 2012, Ohio State University

► A detailed investigation of the Galactic bulge stellar population, based predominantly on… (more)

▼ A detailed investigation of the Galactic bulge stellar population, based predominantly on analysis of OGLE-III photometry, is reported. Significant progress is realized in the areas of variable stars, morphological structure, the red giant branch bump (RGBB), the age-helium-metallicity relationship, and the reddening toward the bulge. It is demonstrated that there is vast discovery potential in the area of Galactic bulge variability studies that is accessible with available technology. The instruments in use for transit surveys are shown to be applicable to microlensing. Separately, detached red giant eclipsing binary pairs are shown to be plentiful, and to be a unique probe of the Galactic bulge age-helium-metallicity relation. The discovery of the Galactic bulge double red clump (RC) is reported and discussed. The distance modulus distribution is shown to bifurcate into a bimodal distribution toward sightlines that are near the bulge minor axis and at least 5 degrees removed from the plane. The discovery of the Galactic bulge RGBB is also reported and discussed. It is shown to be slightly underpopulated and overluminous relative to expectations from stellar models and Galactic globular cluster calibrations, in a manner that can be explained by enhanced helium-enrichment for the Galactic bulge stellar population, with ${Delta}Y ~ + 0.06$ at the median metallicity. An investigation of the RGBB in Galactic globular clusters is conducted to better understand this uncalibrated feature of stellar evolution. Enhanced helium-enrichment is also demonstrated to be a possible solution to the Galactic bulge turnoff age discrepancy. An upper bound on the enhancement of the helium-enhancement, ${Delta}Y ~ + 0.10$, is derived. Finally, the longstanding observational problem of the non-standard optical extinction toward the Galactic bulge is now solved. We combine OGLE-III $VI$ photometry with $VVV$ and $2MASS$ measurements in the near-IR to measure the extinction law $A_{I} = 0.7475{×}E(V-I) + 1.3655{×}E(J-K_{s})$. This two-parameter extinction law, which accounts for the variations in the steepness of the extinction curve, yields a Galactocentric distance $R_{0} = 8.20$ kpc, consistent with geometric determinations. Advisors/Committee Members: Gould, Andrew.

Subjects: Astronomy; Astrophysics

28. Newsham, Grant. The Horizontal Branch as a probe of stellar population history.

Degree: PhD, Astronomy, 2007, Ohio State University

► Color-magnitude diagrams of resolved stellar populations, especially when combined with metal abundance… (more)

Subjects: Physics, Astronomy and Astrophysics

29. Onken, Christopher Alan. Measurement of black hole masses in active Galactic Nuclei.

Degree: PhD, Astronomy, 2005, Ohio State University

► We investigate the calibration and application of reverberation mapping techniques for determining… (more)

▼ We investigate the calibration and application of reverberation mapping techniques for determining black hole (BH)masses in active galactic nuclei (AGNs). We present revised BH mass determinations for several AGNs based on the use of updated methodologies with archival data, demonstrating significant reductions in the sizes of the BH mass uncertainties. Moreover, the study of the Seyfert 1 galaxy, NGC 3783, shows that the gas in the broad-line region of this AGN obeys the virial theorem. We use measurements of stellar velocity dispersions, σ*, in AGNs and the assumption that AGNs follow the same relation between BH mass and σ* as quiescent galaxies to provide the first empirical calibration for reverberation-based BH masses. We also attempt to determine an independent calibration of these masses by studying the reverberation-mapped AGN, NGC 4151, with ground- and space-based observations, and by trying to constrain the BH mass through modeling of the galaxy’s stellar dynamics. We estimate the BH masses and bolometric luminosities in ~400 AGNs selected from the multi-wavelength AGN and Galaxy Evolution Survey (AGES), where the BH masses are calculated from scaling relationships that have grown out of reverberation mapping. We find the distribution of Eddington ratios at fixed luminosity to be sharply peaked around value of 1/3, with a dispersion of just 0.3 dex. The distribution of Eddington ratios at fixed mass looks to be similarly narrow, and we are able to confirm a drop in the underlying distribution at low Eddington ratios for certain combinations of redshift and BH mass – all previous studies in these redshift-mass bins are affected by selection effects at low Eddington ratio (as are the AGES data in lower mass or higher redshift bins). The dominance of AGN accretion at rates relatively close to the Eddington limit has important implications for the growth of BHs and the joint evolution of BHs and their host galaxies. Advisors/Committee Members: Peterson, Bradley M.

Subjects: Physics, Astronomy and Astrophysics

Keywords: AGNs; SWP; NGC; BH mass; BH; MBH; ApJ

30. Peeples, Molly S. From Galaxies to the Intergalactic Medium.

Degree: PhD, Astronomy, 2010, Ohio State University

► Deep in dark matter halos, galaxies are large factories that convert gas… (more)

▼ Deep in dark matter halos, galaxies are large factories that convert gas into stars. Gas is accreted from the expansive intergalactic medium (IGM); stars process this gas by fusing lighter elements into heavier ones. In this Dissertation, I combine both observations and theories from a variety of subfields of astrophysics with analytic and numerical models in an aim for a comprehensive understanding of the underlying physics of star formation feedback, galaxy chemical evolution, and the IGM. The mass-metallicity relation is an observed tight correlation between the stellar masses and gas-phase oxygen abundances of star-forming galaxies. I show that while the intrinsic scatter in this relation is small, extreme outliers do exist; I argue that these outliers have unusual metallicities for their masses because they have unusual gas fractions for their masses. The low-mass high-metallicity galaxies appear to be nearing the end of their star formation, and thus should have abnormally small gas reservoirs with which to dilute their metals. On the other hand, the high-mass low-metallicity galaxies appear to be undergoing gas-rich galaxy mergers, implying that they have larger-than-normal amounts of gas diluting their metals. I then show through analytic arguments that while gas fractions can have a large impact on observed metallicities, the low-redshift mass-metallicity relation is dominated by outflow properties because typical galaxies have relatively small gas fractions. Specifically, the mass-metallicity relation implies that the efficiency with which galaxies expel metals should scale steeply with galaxy mass. Combining this model with reasonable models for star formation feedback, I show that the outflow metallicity should likewise vary with galaxy mass; future measurements of wind metallicity can therefore inform models of the physics underlying galaxy winds. The high-redshift IGM is primarily observed through the Lyman-alpha absorption of neutral hydrogen along the line of sight to a distant quasar. As samples of close quasar pairs increase, so does the amount of potential information in the Lya forest transverse to the line-of-sight. Using two cosmological hydrodynamic simulations with different photoionization heating rates and thus different IGM temperature-density relations, I show that the small-scale structure in the Lya forest along the line of sight is dominated by the current thermal state of the gas. On the other hand, the transverse signal is sensitive to—and thus could be used to place unique constraints on—the thermal history of the gas. Finally, I investigate how a two-phase medium is treated in a suite of idealized smoothed particle hydrodynamic (SPH) simulations. I show that cold, dense spherical blobs become over-pressured relative to their hot, tenuous surroundings, arguing that this is because of an effective numerical surface tension owing to the un-resolveable density discontinuity. I then test one proposed modification to how pressure gradients are calculated in SPH, the so-called "relative pressure SPH" (rpSPH); while rpSPH leads to a more uniform pressure across the simulation, I show that it is ultimately unstable because of its lack of momentum conservation. Advisors/Committee Members: Weinberg, David.

Subjects: Astronomy; Astrophysics

Keywords: IGM; galaxies; star formation feedback; SPH; hydrodynamics; cosmology; galaxy evolution

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