The search for gas in debris discs: ALMA detection of CO gas in HD 36546

TL;DR

This paper reports ALMA observations detecting CO gas in the debris disc of HD 36546, highlighting the presence of secondary gas likely produced by collisions, and provides upper limits for other discs.

Contribution

First detection of CO gas in HD 36546 debris disc using ALMA, supporting the secondary origin hypothesis of gas in debris discs.

Findings

CO gas detected in HD 36546 disc

Upper limits set for other seven discs

Supports secondary origin of gas in debris discs

Abstract

Debris discs represent the last stages of planet formation and as such are expected to be depleted of primordial gas. Nonetheless, in the last few years the presence of cold gas has been reported in $\sim$ 20 debris discs from far-IR to (sub-)mm observations and hot gas has been observed in the optical spectra of debris discs for decades. While the origin of this gas is still uncertain, most evidences point towards a secondary origin, as a result of collisions and evaporation of small bodies in the disc. In this paper, we present ALMA observations aimed at the detection of CO gas in a sample of 8 debris discs with optical gas detections. We report the detection of CO ($^{12}$CO and $^{13}$CO) gas in HD 36546, the brightest and youngest disc in our sample, and provide upper limits to the presence of gas in the remaining seven discs.