The intriguing HI gas in NGC 5253: an infall of a diffuse, low-metallicity HI cloud?

TL;DR

This study reveals that NGC 5253's disturbed HI morphology and kinematics are likely caused by infalling low-metallicity HI gas, triggering a starburst, with evidence of past interaction with M83.

Contribution

It provides new deep HI and radio continuum observations showing disturbed gas morphology and kinematics, and proposes infall of a low-metallicity HI cloud as the starburst trigger.

Findings

NGC 5253 has disturbed HI morphology with tails, plumes, and clouds.

The neutral gas kinematics are highly perturbed and non-rotational.

Evidence suggests infall of a low-metallicity HI cloud along the galaxy's minor axis.

Abstract

(Abridged) We present new, deep HI line and 20-cm radio continuum data of the very puzzling blue compact dwarf galaxy NGC 5253, obtained with the ATCA as part of the `Local Volume HI Survey' (LVHIS). Our low-resolution HI maps show the disturbed HI morphology that NGC 5253 possesses, including tails, plumes and detached HI clouds. The high-resolution map reveals an HI plume at the SE and an HI structure at the NW that surrounds an Ha shell. We confirm that the kinematics of the neutral gas are highly perturbed and do not follow a rotation pattern. We discuss the outflow and infall scenarios to explain such disturbed kinematics, analyze the environment in which it resides, and compare it properties with those observed in similar star-forming dwarf galaxies. The radio-continuum emission of NGC 5253 is resolved and associated with the intense star-forming region at the center of the galaxy. We complete the analysis using multiwavelength data extracted from the literature. We estimate the SFR using this multiwavelength approach. NGC 5253 does not satisfy the Schmidt-Kennicutt law of star-formation, has a very low HI mass-to-light ratio when comparing with its stellar mass, and seems to be slightly metal-deficient in comparison with starbursts of similar baryonic mass. Taking into account all available multiwavelength data, we conclude that NGC 5253 is probably experiencing the infall of a diffuse, low-metallicity HI cloud along the minor axis of the galaxy, which is comprising the ISM and triggering the powerful starburst. The tidally disturbed material observed at the east and north of the galaxy is a consequence of this interaction, which probably started more than 100 Myr ago. The origin of this HI cloud may be related with a strong interaction between NGC 5253 and the late-type spiral galaxy M 83 in the past.