Astronomy
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Item Two Dimensional Velocity Fields of Low Surface Brightness Galaxies(EDP Sciences, 2005) Kuzio de Naray, R.; McGaugh, S. S.; de Blok, W. J. G.; Bosma, A.We present high resolution two dimensional velocity fields from integral field spectroscopy along with derived rotation curves for nine low surface brightness galaxies. This is a positive step forward in terms of both data quality and number of objects studied. We fit NFW and pseudo-isothermal halo models to the observations. We find that the pseudo-isothermal halo better represents the data in most cases than the NFW halo, as the resulting concentrations are lower than would be expected for CDM.Item A Catalog of Low Surface Brightness Galaxies: List II(Copyright American Astronomical Society, 1992-04) SCHOMBERT, JAMES M.; BOTHUN, GREGORY D.; SCHNEIDER, STEPHEN E.; MCGAUGH, STACY S.Item Star Formation Thresholds in Low Surface Brightness Galaxies(Copyright: American Astronomical Society, 1993-08) VAN DER HULST, J. M.; SKILLMAN, E. D.; SMITH, T. R.; BOTHUN, G. D.; MCGAUGH, S. S.; DE BLOK, W. J. G.Item The Balance of Dark and Luminous Mass in Rotating Galaxies(Copyright 2005 The American Physical Society, 2005) McGaugh, Stacy S.baryons to the total rotation velocity increases, the contribution of the dark matter decreases by a compensating amount. This poses a fine-tuning problem for CDM galaxy formation models, and may point to new physics for dark matter particles or even a modification of gravity.Item A Spectral Survey of Black Hole Spin in Active Galactic Nuclei(2007-09-20) Brenneman, Laura; Reynolds, Christopher S.; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation explores the question of whether broad iron lines from the accretion disk can be used as viable diagnostic tools for constraining black hole spin. We begin by giving an overview of the importance of black hole angular momentum as a signature of General Relativity and as a means of testing this theory in the strong-field limit. We discuss the anatomy of the typical black hole/accretion disk system, focusing on the complex environments of active galactic nuclei, and in particular Seyfert-1 systems which we pursue in this work. After developing a robust technique for fitting the continuum and absorption parameters through a rigorous analysis of the XMM-Newton spectrum of the Sy-1 galaxy NGC 4593, we then discuss a new model we have developed that fits broad emission lines from the inner accretion disk. This model, kerrdisk, is fully relativistic and allows the black hole spin to be a free parameter in the fit. Using this model, we carefully analyze the 350 ks XMM-Newton spectrum of the Sy-1 source MCG--6-30-15, which has the broadest and best-studied iron line observed to date. Fitting for the black hole spin in this source, we conclude that a > 0.987 to 90% confidence. We then extend our source list to analyze the XMM-Newton spectra of nine other radio-quiet Sy-1 AGN that have previously been observed to harbor broad iron lines. We find that, given enough photons and a broad line indicative of an origin in the inner disk where relativistic effects are important, our new model enables us to place robust constraints on black hole spin. Four of our sampled AGN meet the criteria necessary to constrain spin. Those constraints are given, along with the full spectral fit to each source. Interestingly, the spins of these sources range from moderate (a ~ 0.5−0.7) to very high (a > 0.95), and we do not find any AGN consistent with non-rotating black holes. For those objects that had marginal spin constraints or none at all, we discuss the spectral fits and the probable reasons for the lack of robustness of our results. This is the first ever survey of black hole spin in type-1 AGN.Item A DEEP X-RAY SURVEY OF THE LOCKMAN HOLE NORTHWEST(2005-08-26) Yang, Yuxuan; Mushotzky, Richard F; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)I present the X-ray analysis of the Chandra Large Area Synoptic X-ray Survey (CLASXS) of the Lockman Hole Northwest field. The contiguous solid angle of the survey is about 0.4 sqr degree and the flux limits are 5x10^-16 erg/cm^2/s in the 0.4-2 keV band and 3x10^-15 erg/cm^2/s in the $2-8$~keV band. The survey bridges the gap between deep pencil beam surveys, and shallower, larger area surveys, allowing a better probe of the X-ray sources that contribute most of the 2--10 keV cosmic X-ray background. A total of 525 X-ray point sources and 4 extended sources have been found. The number counts, X-ray spectra evolution, X-ray variability of the X-ray sources are presented. We show 3 of the 4 extended sources are likely galaxy clusters or galaxy groups. We report the discovery of a gravitational lensing arc associated with one of these sources. I present the spatial correlation function analysis of non-stellar X-ray point sources in the CLASXS and Chandra Deep Field North (CDFN). I calculate both redshift-space and projected correlation functions in comoving coordinates.The correlation function for the CLASXS field over scales of 3 Mpc < s < 200 Mpc can be modeled as a power-law of the form xi(s)=(s/s_0)^{-gamma}, with gamma = 1.6^{+0.4}_{-0.3} and s_0 = 8.05^{+1.4}_{-1.5} Mpc. The redshift-space correlation function for CDFN on scales of 1 Mpc <s < 100 Mpc is found to have a similar correlation length, but a shallower slope. The real-space correlation functions are derived from the projected correlation functions. By comparing the real- and redshift-space correlation functions, we are able to estimate the redshift distortion parameter beta = 0.4 +/- 0.2 at an effective redshift z = 0.94. We found the clustering does not dependence significantly on X-ray color or luminosity. A mild evolution in the clustering amplitude is found, indicating a rapid increase of bias with redshift. The typical mass of the dark matter halo derived from the bias estimates show little change with redshift. The average halo mass is found to be log(M_{halo}/M_sun}) ~ 12.4.