Determining the Origins and Impact of Hot Gas in the Milky Way.

A comprehensive observational and modeling analysis on million degree gas in the Milky Way;Astronomy;Science;Astronomy and Astrophysics

Miller, Matthew J.Gallo, Elena ;

University of Michigan

关键词: A comprehensive observational and modeling analysis on million degree gas in the Milky Way;    Astronomy;    Science;    Astronomy and Astrophysics;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/133282/mjmil_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The Milky Way;;s circumgalactic medium (CGM) contains million degree gas that is volume-filling on >10 kpc scales based on X-ray emission from the ROSAT All-Sky Survey, detections of OVII absorption lines in AGN spectra, ubiquitous detections of OVII-OVIII emission lines in ~1000 blank-sky spectra, and the discovery of the ~10 kpc outflow from the Galactic center known as the Fermi bubbles.Analyses on the line strengths in small samples (<20) constrain the characteristic plasma density, but the dominant hot gas structure is debated in the literature.This is a crucial uncertainty since different galaxy formation mechanisms predict a wide range of hot gas morphologies and masses, and the Fermi bubbles are recently discovered objects that are interacting with the ambient CGM.In this dissertation, I constrain the global hot gas density structure by comparing predictions from parametric density models with all-sky samples of OVII and OVIII line strength measurements.I find that a spherical power law density profile extending to the Milky Way;;s virial radius with a slope of -3/2 reproduces how the absorption and emission line strengths vary across the sky.These results imply the hot gas accounts for less than 50% of the Galactic missing baryons, a hot gas metallicity of greater than one third solar, and that most of the hot gas formed from an accretion shock during the Milky Way;;s formation.I also compare the absorption line shapes and centroids to kinematic models to show that the hot gas rotates with a flat rotation curve of 183 +/- 41 km/s.For the Fermi bubbles, a volume-filled bubble and shell model that is hotter than the surrounding medium and over-pressurized with log(T) = 6.60-6.70 is consistent with the observed line intensities and ratios.I infer a bubble expansion rate, age, and energy injection rate from these constraints, and these results indicate the bubbles likely formed from a Sgr A* accretion event.This analysis uses the most comprehensive observation samples and modeling techniques to reveal how and when million degree gas formed in the Milky Way.