Prof. Dr. Philipp Richter
Project Draft UV-Spectroscopy
The physical properties and kinematics of the circumgalactic medium in the local Universe
It is known that galaxies are surrounded by large amounts of diffuse ionized gas that reflect the on-going formation and evolution of galaxies at low and high redshift. UV absorption spectroscopy represents the most important observational method to trace this so-called circumgalactic medium (CGM), which consists of multi-phase gas spanning a large range in physical conditions. On-going studies using HST/COS indicate the presence of diffuse ionized in the CGM out to the virial radii of the host galaxies (and even beyond), indicating a high morphological complexity of the gas with contributions from fountain-like flows, galactic winds, cold and warm gas accretion flows from the IGM, and tidal gas streams from galaxy interactions.
Yet, because of the limited spectral resolution of COS, the mass estimate and the determination of physical conditions are afflicted with large systematic uncertainties. Only with substantially higher spectral resolution it will be possible to resolve the velocity structure of the CGM absorption features, to disentangle the multiple gas phases in the CGM, and to characterise the interplay between infalling and outflowing gaseous material.
The project will deliver high-resolution UV spectra for a carefully selected sample of background QSOs whose sightlines pass the circumgalactic environment of low-redshift galaxies. The analysis of these data will provide accurate information on column densities of low and high ions together with precise kinematic information, from which the CGM physical properties and spatial structure can be modeled.
Precision measurements such as the ones outlined here will be of great importance to quantify the amount of material that is circulating around galaxies and to reliably determine the gas-accretion rate of galaxies in the local Universe.
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