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2018 Hot Sci @ STScI

Evolution of the Physical Properties of HI-Rich Galaxies across 10 Billion Years

Presented by: Marc Rafelski (STScI/JHU)
Category: Science Colloquia   Duration: 30 minutes   Broadcast date: July 11, 2018
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7/11/18 Marc Rafelski (STScI/JHU) Title: Evolution of the Physical Properties of HI-Rich Galaxies across 10 Billion Years Abstract: Absorption line measurements provide the only means to study the gas that fuels the star formation of the earliest galaxies in the universe. They also provide a unique laboratory to study the metal production, transport, evolution, and distribution of metals in the circumgalactic medium (CGM). Damped Ly-alpha systems (DLAs) trace HI-rich galaxies, dominate the high-z neutral gas content of the Universe, and enable the most robust metallicity measurements of the CGM. Measurements of the chemical evolution of DLAs show a linear decrease in metallicity with increasing redshift, and a sudden decrease at z>4.7. Similarly, the HI mass density is observed to increase, and then either flatten or decrease at z~5. I will present results of a new survey of z>5 quasars to measure the metallicity of z>4.7 DLAs and the HI mass density at the highest possible redshifts to investigate their redshift evolution. I will also present measurements of the SFR efficiency of DLA gas at z~1-3 in the outskirts of star-forming galaxies. Contrary to model predictions of a decreasing SFR efficiency with redshift, we find no significant evolution in the SFR efficiency. Together, these measurements address how the physical properties of the CGM around HI rich galaxies evolve.