Connection Between the Circumgalactic Medium and the Interstellar Medium of Galaxies: Results from the COS-GASS Survey

TL;DR

This study investigates the connection between the circumgalactic medium and the interstellar medium in galaxies, revealing a strong correlation between CGM Lyα absorption and the HI gas fraction, suggesting gas accretion from CGM nourishes the HI disk.

Contribution

It provides new observational evidence linking the properties of the CGM to the HI content in galaxy disks, using UV absorption lines and HI 21cm emission data.

Findings

92% of galaxies show Lyα absorption in CGM

Exponential radial profile of CGM Lyα with scale ~ virial radius

Strong correlation between gas fraction and Lyα equivalent width

Abstract

We present a study exploring the nature and properties of the Circum-Galactic Medium (CGM) and its connection to the atomic gas content in the interstellar medium (ISM) of galaxies as traced by the HI 21cm line. Our sample includes 45 low-z (0.026-0.049) galaxies from the GALEX Arecibo SDSS Survey. Their CGM was probed via absorption in the spectra of background Quasi-Stellar Objects at impact parameters of 63 to 231kpc. The spectra were obtained with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. We detected neutral hydrogen (Ly$\alpha$ absorption-lines) in the CGM of 92% of the galaxies. We find the radial profile of the CGM as traced by the Ly$\alpha$ equivalent width can be fit as an exponential with a scale length of roughly the virial radius of the dark matter halo. We found no correlation between the orientation of sightline relative to the galaxy major axis and the Ly$\alpha$ equivalent width. The velocity spread of the circumgalactic gas is consistent with that seen in the atomic gas in the interstellar medium. We find a strong correlation (99.8% confidence) between the gas fraction (M(HI)/M*) and the impact-parameter-corrected Ly$\alpha$ equivalent width. This is stronger than the analogous correlation between corrected Ly$\alpha$ equivalent width and SFR/M* (97.5% confidence). These results imply a physical connection between the HI disk and the CGM, which is on scales an order-of-magnitude larger. This is consistent with the picture in which the HI disk is nourished by accretion of gas from the CGM.