The extended H i halo of NGC 4945 as seen by MeerKAT

Abstract

Observations of the neutral atomic hydrogen (H i) in the nuclear starburst galaxy NGC 4945 with MeerKAT are presented. We find a large amount of halo gas, previously missed by H i observations, accounting for 6.8% of the total H i mass. This is most likely gas blown into the halo by star formation. Our maps go down to a 3σ column density level of 5 × 1018cm−2. We model the H i distribution using tilted-ring fitting techniques and find a warp on the galaxy’s approaching and receding sides. The H i in the northern side of the galaxy appears to be suppressed. This may be the result of ionisation by the starburst activity in the galaxy, as suggested by a previous study. The origin of the warp is unclear but could be due to past interactions or ram pressure stripping. Broad, asymmetric H i absorption lines extending throughout the H i emission velocity channels are present towards the nuclear region of NGC 4945. Such broad lines suggest the existence of a nuclear ring moving at a high circular velocity. This is supported by the clear rotation patterns in the H i absorption velocity field. The asymmetry of the absorption spectra can be caused by outflows or inflows of gas in the nuclear region of NGC 4945. The continuum map shows small extensions on both sides of the galaxy’s major axis that might be signs of outflows resulting from the starburst activity.

Evidence for extended gaseous reservoirs around AGN at cosmic noon from ALMA CO(3−2) observations

“…The most direct has been the HI line, which traces the atomic medium. Using MeerKAT and its predecessor, studies have revealed ★ E-mail: gareth.jones@physics.ox.ac.uk a diffuse component of HI gas in local starburst galaxies that extends beyond the stellar disk (e.g., Lucero et al 2015;Ianjamasimanana et al 2022). The kinematics of these extended gaseous reservoir differ from those of the disk, suggesting that the gas was expelled by past starburst-driven winds.…”

Gas accretion onto galaxies and Kelvin-Helmholtz turbulence

“…Direct observations are difficult; nevertheless, in recent years observation were made suggesting the existence of such an accretion (Elmegreen, Struck, & Hunter 2014;Elmegreen et al 2016;Kacprzak 2017;Vulcani et al 2018;Zabl et al 2019;Das et al 2020;Luo et al 2021;Ianjamasimanana et al 2022).…”