Over the past decade, Lyman-alpha and metal line absorption observations have established the ubiquity of a gas-rich circumgalactic medium (CGM) around star-forming galaxies at z~0.2 potentially tracing half of the missing baryonic mass within galaxy halos. Unfortunately, these observations only provide a statistical measure of the gas in the CGM and do not constrain the spatial distribution and kinematics of the gas. Furthermore, we have limited sensitivity to Lyman-alpha at z~0 with existing instruments. As such, we remain ignorant of how this gas may flow from the CGM onto the disks of galaxies where it can fuel ongoing star-formation in the present day. Fortunately, 21-cm HI observations with radio telescopes can map HI emission providing both spatial and kinematic information for the CGM in galaxies at z=0. Observations with phased array feeds, radio cameras, on single-dish telescopes yield unmatched surface brightness sensitivity and survey speed. These observations can complete the census of HI in the CGM below N(HI)<10^17 cm^-2 and constrain how gas accretion is proceeding in the local universe, particularly when used in concert with UV absorption line data.
@article{arxiv.1903.07000,
title = {Completing the Hydrogen Census in the Circumgalactic Medium at z~0},
author = {D. J. Pisano and A. Fox and D. French and J. C. Howk and N. Lehner and F. J. Lockman and K. Jones},
journal= {arXiv preprint arXiv:1903.07000},
year = {2019}
}
Comments
Science white paper for the Astro2020 Decadal Survey, 9 pages, 2 figures