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The transformation and evolution of a galaxy is strongly influenced by interactions with its environment. Neutral hydrogen (H  i) is an excellent way to trace these interactions. Here, we present H  i observations of the spiral galaxy NGC 895, which was previously thought to be isolated. High-sensitivity H  i observations from the MeerKAT large survey project MIGHTEE reveal possible interaction features, such as extended spiral arms and the two newly discovered H  i companions, that drive us to change the narrative that it is an isolated galaxy. We combine these observations with deep optical images from the Hyper Suprime Camera to show an absence of tidal debris between NGC 895 and its companions. We do find an excess of light in the outer parts of the companion galaxy MGTH |$\_$| J022138.1-052631, which could be an indication of external perturbation and thus possible sign of interactions. Our analysis shows that NGC 895 is an actively star-forming galaxy with a SFR of 1.75 ± 0.09[M⊙/yr], a value typical for high-stellar mass galaxies on the star-forming main sequence. It is reasonable to state that different mechanisms may have contributed to the observed features in NGC 895, and this emphasizes the need to revisit the target with more detailed observations. Our work shows the high potential and synergy of using state-of-the-art data in both H  i and optical to reveal a more complete picture of galaxy environments. [ABSTRACT FROM AUTHOR]

We report the discovery of large amounts of previously undetected cold neutral atomic hydrogen (H  i) around the core triplet galaxies in the nearby NGC 7232 galaxy group with MeerKAT. With a physical resolution of ∼1 kpc, we detect a complex web of low-surface-brightness H  i emission down to a 4 σ column density level of ∼1 × 1019 cm−2 (over 44  km s−1). The newly discovered H  i streams extend over ∼20 arcmin corresponding to 140 kpc in projection. This is approximately three times the H  i extent of the galaxy triplet (52 kpc). The H  i debris has an H  i mass of ∼6.6 × 109 M⊙, more than 50 per cent of the total H  i mass of the triplet. Within the galaxy triplet, NGC 7233 and NGC 7232 have lost a significant amount of H  i while NGC 7232B appears to have an excess of H  i. The H  i deficiency in NGC 7232 and NGC 7233 indicates that galaxy–galaxy interaction in the group concentrates on this galaxy pair while the other disc galaxies have visited them over time. In comparison to the AMIGA sample of isolated galaxies, we find that with regards to its total H  i mass the NGC 7232/3 galaxy triplet is not H  i -deficient. Despite the many interactions associated to the triplet galaxies, no H  i seems to have been lost from the group (yet). [ABSTRACT FROM AUTHOR]

H  i observations of the nearby blue compact dwarf galaxy IC 10 obtained with the Dominion Radio Astrophysical Observatory synthesis telescope, for a total integration of ∼1000 h, are presented. We confirm the NW faint 21 cm H  i emission feature discovered in Green Bank Telescope (GBT) observations. The H  i feature has an H  i mass of 4.7 × 105 M⊙, which is only ∼0.6  |${{\ \rm per\ cent}}$| of the total H  i mass of the galaxy (7.8 × 107 M⊙). In the inner disc, the rotation curve of IC 10 rises steeply, then flattens until the last point where it rises again, with a maximum velocity of 30 km s−1. Based on our mass models, the kinematics of the inner disc of IC 10 can be described without the need of a dark matter halo. However, this does not exclude the possible presence of dark matter on a larger scale. It is unlikely that the disturbed features seen in the outer H  i disc of IC 10 are caused by an interaction with M 31. Features seen from our simulations are larger and at lower surface density than can be reached by current observations. The higher velocity dispersions seen in regions where several distinct H  i features meet with the main core of IC 10 suggest that there is ongoing accretion. [ABSTRACT FROM AUTHOR]

H i observations of the Local Group dwarf irregular galaxies Sextans A and B, obtained with the Karoo Array Telescope (KAT-7) are presented. The KAT-7 wide field of view and excellent surface brightness sensitivity allows us to verify the true H i extent of the galaxies. We derive H i extends of 30 and 20 arcmin and total H i fluxes of 181 ± 2.0   and 105 ± 1.4 Jy km s−1 for Sextans A and B, respectively. This result shows clearly the overestimate of the H i extent and total flux of 54 arcmin and 264 Jy km s−1 reported for Sextans A using the Effelsberg observations. Tilted ring models allow us to derive the rotation curves (RCs) of Sextans A and B out to 550 arcsec (∼3.5 kpc) and 650 arcsec (∼4 kpc), respectively. The RCs of the two galaxies are seen to decline in the outer parts. The dark matter distribution in Sextans A is better described by the pseudo-isothermal halo model when an M/L ratio of 0.2 is used. For Sextans B, the mass model fits are not as good but again an isothermal sphere with an M/L of 0.2 represents best the data. Using the MOdified Newtonian Dynamics, better fits are obtained when the constant a0 is allowed to vary. The critical densities for gravitational instabilities are calculated using the Toomre-Q and cloud-growth based on shear criterion. We find that in regions of star formation, the cloud growth criterion based on shear explains better the star formation in both Sextans A and B. [ABSTRACT FROM AUTHOR]