A MeerKAT view of pre-processing in the Fornax A group
  We present MeerKAT neutral hydrogen (HI) observations of the Fornax A group,
that is likely falling into the Fornax cluster for the first time. Our HI image
is sensitive to 1.4 x 10$^{19}$ cm$^{-2}$ over 44.1 km s$^{-1}$, where we
detect HI in 10 galaxies and a total of 1.12 x 10$^{9}$ Msol of HI in the
intra-group medium (IGM). We search for signs of pre-processing in the 12 group
galaxies with confirmed optical redshifts that reside within our HI image.
There are 9 galaxies that show evidence of pre-processing and we classify the
pre-processing status of each galaxy, according to their HI morphology and gas
(atomic and molecular) scaling relations. Galaxies yet to experience
pre-processing have extended HI disks, a high HI content with a H$_2$-to-HI
ratio an order of magnitude lower than the median for their stellar mass.
Galaxies currently being pre-processed display HI tails, truncated HI disks
with typical gas ratios. Galaxies in the advanced stages of pre-processing are
HI deficient. If there is any HI, they have lost their outer HI disk and
efficiently converted their HI to H$_2$, resulting in H$_2$-to-HI ratios an
order of magnitude higher than the median for their stellar mass. The central,
massive galaxy in our group underwent a 10:1 merger 2 Gyr ago, and ejected 6.6
- 11.2 x 10$^{8}$ Msol of HI that we detect as clouds and streams in the IGM,
some forming coherent structures up to 220 kpc in length. We also detect giant
(100 kpc) ionised hydrogen (H$\alpha$) filaments in the IGM, likely from cool
gas being removed (and ionised) from an infalling satellite. The H$\alpha$
filaments are situated within the hot halo of NGC 1316 and some regions contain
HI. We speculate that the H$\alpha$ and multiphase gas is supported by magnetic
pressure (possibly assisted by the AGN), such that the hot gas can condense and
form HI that survives in the hot halo for cosmological timescales.
