The Baryonic Tully-Fisher Relation cares about the Galaxy Sample
  The Baryonic Tully-Fisher relation (BTFR) is a clear manifestation of the
underlying physics of galaxy formation. As such, it is used to constrain and
test galaxy formation and evolution models. Of particular interest, apart from
the slope of the relation, is its intrinsic scatter. In this paper, we use the
EAGLE simulation to study the dependence of the BTFR on the size of the
simulated galaxy sample. The huge number of datapoint available in the
simulation is indeed not available with current observations. Observational
studies that computed the BTFR used various (small) size samples with the only
obligation to have galaxies spanning over a large range of masses and rotation
rates. Accordingly, to compare observational and theoretical results, we build
a large number of various size datasets using the same criterion and derive the
BTFR for all of them. Unmistakably, their is an effect of the number of
galaxies used to derive the relation. The smaller the number, the larger the
standard deviation around the average slope and intrinsic scatter of a given
size sample of galaxies. This observation allows us to alleviate the tensions
between observational measurements and LCDM predictions. Namely, the size of
the observational samples adds up to the complexity in comparing observed and
simulated relations to discredit or confirm LCDM. Similarly, samples, even
large, that do not reflect the galaxy distribution give on average biased
results. Large size samples reproducing the underlying distribution of galaxies
constitute a supplementary necessity to compare efficiently observations and
simulations.
