WALLABY Early Science - III. An HI Study of the Spiral Galaxy NGC 1566
  This paper reports on the atomic hydrogen gas (HI) observations of the spiral
galaxy NGC 1566 using the newly commissioned Australian Square Kilometre Array
Pathfinder (ASKAP) radio telescope. We measure an integrated HI flux density of
$180.2$ Jy km s$^{-1}$ emanating from this galaxy, which translates to an HI
mass of $1.94\times10^{10}$M$_\circ$ at an assumed distance of $21.3$ Mpc. Our
observations show that NGC 1566 has an asymmetric and mildly warped HI disc.
The HI-to-stellar mass fraction of NGC 1566 is $0.29$, which is high in
comparison with galaxies that have the same stellar mass
($10^{10.8}$M$_\circ$). We also derive the rotation curve of this galaxy to a
radius of $50$ kpc and fit different mass models to it. The NFW, Burkert and
pseudo-isothermal dark matter halo profiles fit the observed rotation curve
reasonably well and recover dark matter fractions of $0.62$, $0.58$ and $0.66$,
respectively. Down to the column density sensitivity of our observations
($N_{HI} = 3.7\times10^{19}$ cm$^{-2}$), we detect no HI clouds connected to,
or in the nearby vicinity of, the HI disc of NGC 1566 nor nearby interacting
systems. We conclude that, based on a simple analytic model, ram pressure
interactions with the IGM can affect the HI disc of NGC 1566 and is possibly
the reason for the asymmetries seen in the HI morphology of NGC 1566.
