Possible origins of anomalous HI gas around MHONGOOSE galaxy, NGC 5068

Abstract

The existing reservoirs of neutral atomic hydrogen gas (HI) in galaxies are insufficient to have maintained the observed levels of star formation without some kind of replenishment. {This refuelling of the HI reservoirs} is likely to occur at column densities an order of magnitude lower than previous observational limits (N${}_{\mathrm{H}\mathrm{I}\mathrm{limit}}\sim 10^{19}$cm${}^{-2}$ at 30${}^{\prime \prime }$ resolution over a linewidth of $20$km/s). In this paper, we present recent deep HI observations of NGC 5068, a nearby isolated star-forming galaxy observed by MeerKAT as part of the MHONGOOSE survey. With these new data, we are able to detect low column density HI around NGC 5068 with a $3\sigma$ detection limit of N${}_{\mathrm{H}\mathrm{I}}=6.4\times 10^{17}$cm${}^{-2}$ at 90${}^{\prime \prime }$ resolution over a $20$km/s linewidth. The high sensitivity and resolution of the MeerKAT data reveal a complex morphology of the HI in this galaxy -- a regularly rotating inner disk coincident with the main star-forming disk of the galaxy, a warped outer disk of low column density gas (N${}_{\mathrm{H}\mathrm{I}}<9\times 10^{19}$cm${}^{-2}$), in addition to clumps of gas on the north west side of the galaxy. We employ a simple two disk model that describe the inner and outer disks, and are able to identify anomalous gas that deviates from the rotation of the main galaxy. The morphology and the kinematics of the anomalous gas suggest a possible extra-galactic origin. We explore a number of possible origin scenarios that may explain the anomalous gas, and conclude that fresh accretion is the most likely scenario.

17 pages, 13 figures, 5 tables. Accepted for publication in A&A

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Cited by in corpus (4)

• MHONGOOSE -- A MeerKAT Nearby Galaxy HI Survey
• PHANGS-MeerKAT and MHONGOOSE HI observations of nearby spiral galaxies: physical drivers of the molecular gas fraction, $R_{\mathrm{mol}}$
• Uncovering Extraplanar Gas in UGCA 250 with the Ultra-deep MHONGOOSE Survey
• Hot accretion onto spiral galaxies: the origin of extended and warped HI discs