Halo shapes constrained from a pure sample of central galaxies in
  KiDS-1000
  We present measurements of $f_h$, the ratio of the aligned components of the
projected halo and galaxy ellipticities, for a sample of central galaxies using
weak gravitational lensing data from the Kilo-Degree Survey (KiDS). Using a
lens galaxy shape estimation that is more sensitive to outer galaxy regions, we
find $f_{\rm h}=0.50\pm0.20$ for our full sample and $f_{\rm h}=0.55\pm0.19$
for an intrinsically red (and therefore higher stellar-mass) sub-sample,
rejecting the hypothesis of round halos and/or galaxies being un-aligned with
their parent halo at $2.5\sigma$ and $2.9\sigma$, respectively. We quantify the
93.4% purity of our central galaxy sample using numerical simulations and
overlapping spectroscopy from the Galaxy and Mass Assembly survey. This purity
ensures that the interpretation of our measurements is not complicated by the
presence of a significant fraction of satellite galaxies. Restricting our
central galaxy ellipticity measurement to the inner isophotes, we find $f_{\rm
h}=0.34\pm0.17$ for our red sub-sample, suggesting that the outer galaxy
regions are more aligned with their dark matter halos compared to the inner
regions. Our results are in agreement with previous studies and suggest that
lower mass halos are rounder and/or less aligned with their host galaxy than
samples of more massive galaxies, studied in galaxy groups and clusters.
