Anomalous gas in ESO 149-G003: A MeerKAT-16 View

TL;DR

This study uses MeerKAT and MeerLICHT observations to confirm anomalous and extraplanar neutral hydrogen in the isolated dwarf galaxy ESO 149-G003, revealing ongoing gas accretion processes.

Contribution

First detailed kinematic analysis of anomalous HI in ESO 149-G003 using MeerKAT, confirming extraplanar gas and estimating its mass fraction.

Findings

At least 7-8% of HI exhibits anomalous kinematics.

Less than 1% of HI is extraplanar and morphologically confirmed.

The galaxy is likely acquiring gas through accretion.

Abstract

ESO 149-G003 is a close-by, isolated dwarf irregular galaxy. Previous observations with the ATCA indicated the presence of anomalous neutral hydrogen (HI) deviating from the kinematics of a regularly rotating disc. We conducted follow-up observations with the MeerKAT radio telescope during the 16-dish Early Science programme as well as with the MeerLICHT optical telescope. Our more sensitive radio observations confirm the presence of anomalous gas in ESO 149-G003, and further confirm the formerly tentative detection of an extraplanar HI component in the galaxy. Employing a simple tilted-ring model, in which the kinematics is determined with only four parameters but including morphological asymmetries, we reproduce the galaxy's morphology, which shows a high degree of asymmetry. By comparing our model with the observed HI, we find that in our model we cannot account for a significant (but not dominant) fraction of the gas. From the differences between our model and the observed data cube we estimate that at least 7%-8% of the HI in the galaxy exhibits anomalous kinematics, while we estimate a minimum mass fraction of less than 1% for the morphologically confirmed extraplanar component. We investigate a number of global scaling relations and find that, besides being gas-dominated with a neutral gas-to-stellar mass ratio of 1.7, the galaxy does not show any obvious global peculiarities. Given its isolation, as confirmed by optical observations, we conclude that the galaxy is likely currently acquiring neutral gas. It is either re-accreting gas expelled from the galaxy or accreting pristine intergalactic material.