313 research outputs found
Examining The Bullet Cluster: Pairwise Velocity Distributions in a Large N-Body Cosmological Simulation
No full textThe Quasar Proximity Effect and the Intergalactic Medium at Low Redshift
No full textIn this work, I determine the quasar (QSO) proximity effect at low redshift (z~14.5-15. The proximity effect is not present for weaker column density lines of 13<~logN<~14.5-15. I conduct an analysis of these observations to find more detailed trends within the proximity zone, such as a lack of additional thermal broadening in the absorption lines with respect to the broadening seen in the area outside of the proximity zone. After highlighting the lack of current data at these lower redshifts I discuss multiple models predicting the quasar proximity effect, structure formation, quasar lifetime constraints, the neutral hydrogen column density distribution, and the evolution of ionization in the intergalactic medium (IGM), especially at redshifts of z<2
The Baryon Content of Galaxy Systems: Observations and Simulations
No full textThe distribution of baryons in the universe tells us about the evolution and processes occurring within galaxies and clusters. Attempts to probe the gas within these structures have revealed a significantly lower baryon content than the cosmic fraction of (as determined by CMB observations). However, most of these observational methods (namely X-ray and SZ) are only sensitive enough to measure a small fraction of the whole virialized volume. By using a combination of observational data and extrapolation to larger radii, in addition to a few particularly deep observations which extend to the virial radius, we may successfully account for these ``missing baryons." We also analyze galaxy clusters within several high-resolution cosmological simulations to see how well they reproduce observed trends in gas, stellar and dark matter distribution. We find that for systems with masses ranging from , the baryon content achieves the cosmic fraction at slightly past the virial radius. Expelled from the cores of their clusters by feedback processes (shock heating, supernovae and potentially AGN), these baryons reside in the halos in the form of hot plasma. Simulations confirm the existence of significant amounts of gas on these scales. However, overall consistency with observations varies depending on the specific physics included in the simulations, and how it is implemented
Clusters of Galaxies: Mass Determination Methods, Biases, And Precision Cosmology
No full textThe mass-function of galaxy clusters in the Universe reveals information about the formation, evolution, and processes behind celestial objects. Previous attempts to probe masses of clusters have depended on various methods, including kinematics and dynamics, X-ray observations, and gravitational lensing. When studies use X-ray observations to derive cluster masses, they assume that the gas within the cluster is in hydrostatic equilibrium (HSE). The problem with this assumption is that clusters are not necessarily in HSE. As such, HSE mass measurements are often compared with more reliable lensing masses in order to reveal the systematic bias of the HSE assumption. In this work, we investigate the uncertainties in the bias of mass determination for a sample of 25 galaxy clusters using precision cosmology. This will enable the use of clusters -- the most massive virialized systems in the universe -- as accurate tools in determining cosmological parameters including the dark-matter and dark-energy density of the universe. In this work, we measure a mean mass bias of -- consistent with the current literature
Simulation Analysis of High-Mass X-Ray Binaries as Merging Binary Black Hole Progenitors
No full textBinary black holes (BBHs) as observed by the Laser Interferometer Gravitational–Wave Observatory (LIGO) and the Virgo Interferometer are thought to experience a high mass x–ray binary (HMXB) phase. However, at most 3 HMXBs observed in x–ray are predicted to be LIGO–Virgo BBH progenitors, and there are uncertainties regarding these predictions. The lack of x–ray observations of these progenitors raises the question of whether we expect to see such systems in standard models of stellar evolution. It also opens the possibility that we can constrain uncertainties in binary evolution through the absence of HMXB detections and determine if these systems could be targets for future x–ray surveys. We use the COSMIC population synthesis code to simulate a large population of double compact object systems at 1/10 Z _{\odot}, and find that 99.98% of LIGO–Virgo BBH progenitors achieve HMXB luminosities above the 10^{35} erg s^{−1} observable threshold. Most of these binaries emit above this threshold for 0.5-2.0 Myr, and their luminosities exceed 10^{37} erg s^{−1} for a majority of that time. We identify clear correlations between the peak luminosity, duration of observable emission, system mass, and binary separation for LIGO–Virgo BBH progenitors. Finally, we calculate that, at low metallicity, 41.8% of observable HMXBs will become LIGO–Virgo BBHs
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