A Multi-Sightline Investigation of the Complex Circumgalactic Medium

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Astronomers seek to understand how stars and galaxies formed. Galaxies exist in relation to the diffuse gas that surrounds them. Understanding this relationship is essential for understanding how galaxies, including our own galaxy (the Milky Way), came into being. To probe diffuse gas, astronomers use fortuitously aligned, bright background sources that illuminate it. Chen and collaborators take this method one step further. They use background sources that have been gravitationally lensed to yield multiple images. These images probe the gas from multiple lines of sight simultaneously. This project will produce the first survey of such galaxies and gas together. Investigators will discover the properties of this gas, including its spatial distribution. They will understand the inter-relationship between the surrounding gas and galaxies within. The PI will interact with underrepresented minority high school students through the Space Explorers Program. The PI will also engage undergraduates in summer research and support one PhD thesis. The PI will collaborate with Adler Planetarium to develop museum displays that communicate key findings of galaxy evolution. These activities inspire young people and the general public to participate in science.This proposed investigation utilizes multiply-lensed quasars (QSOs) and projected QSO pairs to resolve the motion and chemical enrichment of the CircumGalactic Medium (CGM). The galaxies span a range of morphologies and star formation histories. Specific scientific objectives include characterizing the diffuse gas halos, particularly its velocity distribution, its dependence upon galaxy properties, and its mechanism of formation. This project will produce the first large survey of dozens (~60) of spatially and spectrally resolved halo maps at projected distance d 100 kpc around both star-forming and passive galaxies in the range 0.4 z 1. This project extends prior studies by going to higher redshift and increasing sample size by an order of magnitude. It will contribute a deeper understanding of the relationship between diffuse CGM halo gas and star formation in galaxies.