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We combine new and archival Multi-unit spectroscopic explorer (MUSE) observations with data from the MeerKAT Fornax Survey and the ALMA Fornax Cluster Survey to study the ionized, atomic, and molecular gas in six gas-rich dwarf galaxies in the Fornax cluster in detail. We compare the distributions and velocity fields of the three gas phases with each other, with MUSE white-light images, and with the stellar velocity fields. Additionally, we derive the resolved molecular Kennicutt–Schmidt relation for each object, and compare these with existing relations for field galaxies and for the Fornax and Virgo clusters. Finally, we explore global measurements such as gas deficiencies and star formation rates to paint as complete a picture of their evolutionary state as possible. We find that all six gas-rich dwarf galaxies have very disturbed interstellar medium, with all three gas phases being irregular both in terms of spatial distribution and velocity field. Most objects lie well below the Kennicutt–Schmidt relations from the literature. Furthermore, they are quite deficient in H i (with def$_{{\rm{H}{\small I}}}$ between $\sim$1 and $\sim$2 dex), and moderately deficient in H$_2$ (with def$_{\mathrm{ H}_{2}}$ between $\sim$0 and $\sim$1), suggesting that, while both cold gas phases are affected simultaneously, H i is removed in significant quantities before H$_2$. We suggest that these dwarfs are on their first infall into the cluster, and are in the process of transitioning from star-forming to passive. A combination of tidal interactions, mergers/pre-processing, and ram pressure stripping is likely responsible for these transformations.

We conducted the MeerKAT Vela Supercluster survey, named Vela$-$$\textrm {H}\, \scriptstyle \mathrm{I}$, to bridge the gap between the Vela SARAO (South African Radio Astronomy Observatory) MeerKAT Galactic Plane Survey (Vela$-$SMGPS, $-2^{\circ } \le b \le 1^{\circ }$), and optical and near-infrared spectroscopic observations of the Vela Supercluster (hereafter Vela$-$OPT/NIR) at $|b| \gtrsim 7^{\circ }$. Covering coordinates from $263^{\circ } \le \ell \le 284^{\circ }$ and $1^{\circ } \le b \le 6.2^{\circ }$ above, and $-6.7^{\circ } \le b \le -2^{\circ }$ below the Galactic Plane (GP), we sampled 667 fields spread across an area of ${\sim } \rm 242 ~deg^2$. With a beam size of ${\sim } 38 \ \mathrm{ arcsec} \times 31 \ \mathrm{ arcsec}$, Vela$-$$\textrm {H}\, \scriptstyle \mathrm{I}$ achieved a sensitivity of $\langle \rm rms \rangle = 0.74$$\rm mJy\, beam^{-1}$ at 44.3 $\rm km\, s^{-1}$ velocity resolution over ${\sim }$67 h of observations. We catalogued 719 galaxies, with only 211 (29 per cent) previously documented in the literature, primarily through the H i Parkes Zone of Avoidance survey (HIZOA), Two Micron All-sky Survey Extended Source Catalog (2MASX), and Wide-field Infrared Survey Explorer (WISE) data bases. Among these known galaxies, only 66 had optical spectroscopic redshift information. We found marginal differences of less than one channel resolution for all galaxies in common between HIZOA and Vela$-$SMGPS, and a mean difference of $70 \pm 15$$\rm km\, s^{-1}$ between optical and $\textrm {H}\, \scriptstyle \mathrm{I}$ velocities. Combining data from Vela$-$SMGPS, Vela$-$$\textrm {H}\, \scriptstyle \mathrm{I}$, and Vela$-$OPT/NIR confirmed the connection of the Hydra/Antlia filament across the GP and revealed a previously unknown diagonal wall at a heliocentric velocity range of $6500\!\!-\!\!8000$$\rm km\, s^{-1}$. Vela$-$$\textrm {H}\, \scriptstyle \mathrm{I}$ reinforces the connection between the first wall at $18\,500\!\!-\!\!20\,000$$\rm km\, s^{-1}$ and the inner Zone of Avoidance. The second wall seems to traverse the GP at $270^{\circ } \le \ell \le 279^{\circ }$, where it appears that both walls intersect, jointly covering the velocity range $18\,500\!\!-\!\!21\,500$$\rm km\, s^{-1}$.

The presence of dense, neutral hydrogen clouds in the hot, diffuse intragroup and intracluster (IC) medium is an important clue to the physical processes controlling the survival of cold gas and sheds light on cosmological baryon flows in massive halos. Advances in numerical modeling and observational surveys mean that theory and observational comparisons are now possible. In this paper, we use the high-resolution TNG50 cosmological simulation to study the Hidistribution in seven halos with masses similar to the Fornax galaxy cluster. Adopting observational sensitivities similar to the MeerKAT Fornax Survey (MFS), an ongoing Hisurvey that will probe to column densities of 10¹⁸cm⁻², we find that Fornax-like TNG50 halos have an extended distribution of neutral hydrogen clouds. Within 1R_vir, we predict the MFS will observe a total Hicovering fraction of ∼12% (mean value) for 10 kpc pixels and 6% for 2 kpc pixels. If we restrict this to gas more than 10 half-mass radii from galaxies, the mean values only decrease mildly, to 10% (4%) for 10 (2) kpc pixels (albeit with significant halo-to-halo spread). Although there are large amounts of Hioutside of galaxies, the gas seems to be associated with satellites, judging both by the visual inspection of projections and by comparison of the line of sight velocities of galaxies and IC Hi.