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You searched for +publisher:"University of Michigan" +contributor:("Sharon, Keren"). Showing records 1 – 3 of 3 total matches.

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University of Michigan

1. Johnson, Traci. Focusing Cosmic Telescopes: Quantifying the Systematics of Strong Lensing Mass Models in the Era of Precision Lensing.

Degree: PhD, Astronomy and Astrophysics, 2018, University of Michigan

Massive galaxy clusters are capable of magnifying background sources and thus act as natural telescopes to the distant Universe. My dissertation focuses on modeling the mass distributions of these clusters in order to determine to what degree intrinsic properties of background sources such as luminosity, star formation rate, and size have been magnified. With accurate and precise lens models, we can compute the luminosity functions of the most distant galaxies at z > 8, pushing beyond the limits of HST deep fields, which will help to understand the formation of galaxies during the epoch of re-ionization. We can also use cluster lensing to zoom into galaxies at z ~ 2 to study their star formation morphologies on scales smaller than a kiloparsec, science that will not be feasible for field galaxies until JWST comes online. In addition to creating lens models, my dissertation also looks at the systematic errors associated with lens modeling techniques. As I will show, lens model accuracy can depend on the number of constraints as well as the availability of spectroscopic redshifts used in the modeling process. Understanding the systematic errors of lens models will be necessary in the next decade, when several wide-field surveys will reveal thousands of new strong lensing systems, for which higher resolution imaging and spectroscopic data may not be obtained for all systems. Advisors/Committee Members: Sharon, Keren (committee member), Evrard, August (committee member), Kneib, Jean-Paul (committee member), Miller, Christopher John (committee member), Miller, Jon Matthew (committee member).

Subjects/Keywords: gravitational lensing; galaxy clusters; Astronomy; Science

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Johnson, T. (2018). Focusing Cosmic Telescopes: Quantifying the Systematics of Strong Lensing Mass Models in the Era of Precision Lensing. (Doctoral Dissertation). University of Michigan. Retrieved from http://hdl.handle.net/2027.42/144156

Chicago Manual of Style (16th Edition):

Johnson, Traci. “Focusing Cosmic Telescopes: Quantifying the Systematics of Strong Lensing Mass Models in the Era of Precision Lensing.” 2018. Doctoral Dissertation, University of Michigan. Accessed August 20, 2019. http://hdl.handle.net/2027.42/144156.

MLA Handbook (7th Edition):

Johnson, Traci. “Focusing Cosmic Telescopes: Quantifying the Systematics of Strong Lensing Mass Models in the Era of Precision Lensing.” 2018. Web. 20 Aug 2019.

Vancouver:

Johnson T. Focusing Cosmic Telescopes: Quantifying the Systematics of Strong Lensing Mass Models in the Era of Precision Lensing. [Internet] [Doctoral dissertation]. University of Michigan; 2018. [cited 2019 Aug 20]. Available from: http://hdl.handle.net/2027.42/144156.

Council of Science Editors:

Johnson T. Focusing Cosmic Telescopes: Quantifying the Systematics of Strong Lensing Mass Models in the Era of Precision Lensing. [Doctoral Dissertation]. University of Michigan; 2018. Available from: http://hdl.handle.net/2027.42/144156


University of Michigan

2. Gifford, Daniel William. Estimating Cosmological Parameters and Cluster Masses through Escape Velocity Measurements in Galaxy Clusters.

Degree: PhD, Astronomy and Astrophysics, 2016, University of Michigan

Galaxy clusters are large virialized structures that exist at the intersection of filaments of matter that make up the cosmic web. Due to their hierarchical growth history, they are excellent probes of the cosmology that governs our universe. Here, we aim to use clusters to better constrain cosmological parameters by systematically studying the uncertainties on galaxy cluster mass estimation for use in a halo mass function analysis. We find that the caustic technique is capable on average of recovering unbiased cluster masses to within 30% for well sampled systems. We also quantify potential statistical and systematic biases due to observational challenges. To address statistical biases in the caustic technique, we developed a new stacking algorithm to measure the average cluster mass for a single stack of projected cluster phase-spaces. By varying the number of galaxies and number of clusters we stack, we find that the single limited value is the total number of galaxies in the stack opening up the possibility for self-calibrated mass estimates of low mass or poorly sampled clusters in large surveys. We then utilize the SDSS-C4 catalog of galaxy clusters to place some of the tightest galaxy cluster based constraints on the matter density and power spectrum normalization for matter in our universe. Advisors/Committee Members: Miller, Christopher John (committee member), Evrard, August (committee member), Gnedin, Oleg (committee member), Sharon, Keren (committee member).

Subjects/Keywords: Cosmology; Galaxy Clusters; Extragalactic; Astronomy; Science

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Gifford, D. W. (2016). Estimating Cosmological Parameters and Cluster Masses through Escape Velocity Measurements in Galaxy Clusters. (Doctoral Dissertation). University of Michigan. Retrieved from http://hdl.handle.net/2027.42/120771

Chicago Manual of Style (16th Edition):

Gifford, Daniel William. “Estimating Cosmological Parameters and Cluster Masses through Escape Velocity Measurements in Galaxy Clusters.” 2016. Doctoral Dissertation, University of Michigan. Accessed August 20, 2019. http://hdl.handle.net/2027.42/120771.

MLA Handbook (7th Edition):

Gifford, Daniel William. “Estimating Cosmological Parameters and Cluster Masses through Escape Velocity Measurements in Galaxy Clusters.” 2016. Web. 20 Aug 2019.

Vancouver:

Gifford DW. Estimating Cosmological Parameters and Cluster Masses through Escape Velocity Measurements in Galaxy Clusters. [Internet] [Doctoral dissertation]. University of Michigan; 2016. [cited 2019 Aug 20]. Available from: http://hdl.handle.net/2027.42/120771.

Council of Science Editors:

Gifford DW. Estimating Cosmological Parameters and Cluster Masses through Escape Velocity Measurements in Galaxy Clusters. [Doctoral Dissertation]. University of Michigan; 2016. Available from: http://hdl.handle.net/2027.42/120771


University of Michigan

3. Ludlam, Renee. A Hard Look at Accretion Around Neutron Stars.

Degree: PhD, Astronomy and Astrophysics, 2019, University of Michigan

Neutron stars (NSs) are the most compact objects with a surface in the Universe. The only way to understand how matter behaves under the conditions found in NSs is to determine the equation of state (EoS) of ultradense, cold matter. The EoS sets the radius for a NS of a given mass, therefore, measurements of masses and radii can be used to rule out or confirm theoretical EoSs. One method to determine radii of NSs utilizes atomic lines that arise from the inner region of the accretion disk. These lines are broadened due to Doppler and relativistic effects from the motion of the disk and extreme gravity near the NS. The resolution and sensitivity of NuSTAR in the 3-79 keV bandpass have provided an unprecedented look at the innermost accretion flow onto NSs. Numerous observations have revealed clear disk reflection spectra, unbiased by detector effects or modeling degeneracies. In this dissertation I demonstrate the importance of these features in determining properties of the accretion disk and NS in low-mass X-ray binaries (LMXBs). The discovery of multiple emission lines that originate from different ionization states - and presumably radii - within the disk are presented in Chapter 2. Modeling of these lines does not return distinct radii, but this is promising nonetheless for future endeavors that can capture these features with higher signal-to-noise. In Chapter 3, a sample of persistently accreting NSs reveals tight constraints on the position on the inner disk close to the NS. This allows for regions on the mass-radius plane to be traced out, which are already comparable to constraints obtained from other methods to determine NS mass and radius. Moreover, in Chapter 4 I perform the first reflection study of the NS transient XTE J1709-267 as the source transitions to a higher accretion rate. Hence, I analyze these states separately to track changes in the inner accretion disk, but disk properties remain consistent. In Chapter 5, I demonstrate that Fe lines can be used to estimate the magnetic field strength in these systems to first-order by comparing to estimates from pulsations seen in accreting millisecond X-ray pulsars. With the growing number of NuSTAR observations of reflection spectra in NS LMXBs, I am able to look at the sample as a whole to explore how the inner disk radius changes as a function of mass accretion rate (Chapter 6). There is no clear correlation between the inner disk position and mass accretion rate; confirming previous studies. The recent launch of NICER now affords the opportunity to search for low-energy relativistic lines down to 0.25 keV using detectors that are also free of distortions at high flux levels. In Chapter 7, I perform the first NICER spectral study using observations of Serpens X-1. This confirmed the reflection nature of the Fe L blend for the first time in a NS system. Reflection studies of NS LMXBs provides information on NS radii, magnetic field strengths, potential boundary layers between the inner accretion flow and NS surface, as well as properties of the… Advisors/Committee Members: Miller, Jon Matthew (committee member), Evrard, August (committee member), Gultekin, Kayhan (committee member), Harrison, Fiona Anne (committee member), Sharon, Keren (committee member).

Subjects/Keywords: Neutron star; Accretion; X-rays; Astronomy; Science

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Ludlam, R. (2019). A Hard Look at Accretion Around Neutron Stars. (Doctoral Dissertation). University of Michigan. Retrieved from http://hdl.handle.net/2027.42/150033

Chicago Manual of Style (16th Edition):

Ludlam, Renee. “A Hard Look at Accretion Around Neutron Stars.” 2019. Doctoral Dissertation, University of Michigan. Accessed August 20, 2019. http://hdl.handle.net/2027.42/150033.

MLA Handbook (7th Edition):

Ludlam, Renee. “A Hard Look at Accretion Around Neutron Stars.” 2019. Web. 20 Aug 2019.

Vancouver:

Ludlam R. A Hard Look at Accretion Around Neutron Stars. [Internet] [Doctoral dissertation]. University of Michigan; 2019. [cited 2019 Aug 20]. Available from: http://hdl.handle.net/2027.42/150033.

Council of Science Editors:

Ludlam R. A Hard Look at Accretion Around Neutron Stars. [Doctoral Dissertation]. University of Michigan; 2019. Available from: http://hdl.handle.net/2027.42/150033

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