The MeerKAT Fornax Survey: removal of HI gas from galaxies in the Fornax cluster

Abstract: The MeerKAT Fornax Survey is conducting a thorough examinationof the nearby Fornax galaxy cluster to understand how galaxies lose their cold gas and stop forming stars in low-mass clusters (M${\rm vir} \leq 10^{14}$ M$\odot$). We are doing so through very deep (down to $\sim 10^{18}$ cm$^{-2}$) and high resolution (up to$\sim~ 1$ kpc and 1 km s$^{-1}$) MeerKAT observations of neutral atomic hydrogen gas (HI) in a $1\times2$ Mpc$^2$ region centred on Fornax. At the time of writing, the survey is $88\%$ complete. Initial analysis of the cluster's central area has unveiled the widespread existence of previously unseen HI tails and clouds. Some of the HI is clearly being removed from Fornax galaxies as they interact with one another or with the intra-cluster medium. We present a sample of galaxies with long, one-sided, star-less HI tails (of which only one was previously known) radially oriented within the cluster. The properties of these tails represent the first conclusive evidence that ram pressure is a key force shaping the distribution of HI in the Fornax cluster. Furthermore, interactions within the Fornax environment shape the HI mass function, the HI content of dwarf galaxies and determines how the HI sustains the nuclear activity of some cluster members and neighbouring galaxies.