Constraints on the gas masses of low-z damped Lyman-$\alpha$ systems

TL;DR

This study used the Green Bank Telescope to search for HI 21 cm emission in low-redshift damped Lyman-alpha systems, finding non-detections that imply these absorbers are associated with low-mass, gas-poor galaxies.

Contribution

First deep HI 21 cm emission search for low-z DLAs providing constraints on galaxy gas masses, confirming low HI masses in such systems.

Findings

No HI 21 cm emission detected in two of three absorbers.

Upper limits on HI mass are below 2.7 x 10^9 solar masses.

Low HI masses suggest low-z DLAs are not in massive, gas-rich galaxies.

Abstract

We report a deep search for redshifted HI 21 cm emission from three damped and sub-damped Lyman-$\alpha$ absorbers (DLAs) at $z \approx 0.1$ with the Green Bank Telescope (GBT). No evidence for a redshifted HI 21 cm emission signal was obtained in the GBT spectra of two absorbers, with the data on the third rendered unusable by terrestrial interference. The non-detections of HI 21 cm emission yield strong constraints on the HI masses of the associated galaxies, M$_{\rm HI} < 2.3 \times 10^9 \times (\Delta V/100)^{1/2}$ M$_\odot$ for the sub-DLA at $z = 0.0830$ towards J1553+3548, and M$_{\rm HI} < 2.7 \times 10^9 \times (\Delta V/100)^{1/2}$ M$_\odot$ for the DLA at $z = 0.0963$ towards J1619+3342, where $\Delta V$ is the HI 21 cm line width, in km s$^{-1}$. This continues the trend of low HI masses found in all low-$z$ DLAs and sub-DLAs that have been searched for redshifted HI 21 cm emission. Low-redshift absorbers with relatively low HI column densities, $\lesssim few \times 10^{20}$ cm$^{-2}$, thus do not typically arise in massive gas-rich galaxies.