On the evidence for large-scale galactic conformity in the local
  Universe
  We re-examine the observational evidence for large-scale (4 Mpc) galactic
conformity in the local Universe, as presented in Kauffmann et al. (2013). We
show that a number of methodological features of their analysis act to produce
a misleadingly high amplitude of the conformity signal. These include a
weighting in favour of central galaxies in very high-density regions, the
likely misclassification of satellite galaxies as centrals in the same
high-density regions, and the use of medians to characterize bimodal
distributions. We show that the large-scale conformity signal in Kauffmann et
al. clearly originates from a very small number of central galaxies in the
vicinity of just a few very massive clusters, whose effect is strongly
amplified by the methodological issues that we have identified. Some of these
'centrals' are likely misclassified satellites, but some may be genuine
centrals showing a real conformity effect. Regardless, this analysis suggests
that conformity on 4 Mpc scales is best viewed as a relatively short-range
effect (at the virial radius) associated with these very large neighbouring
haloes, rather than a very long-range effect (at tens of virial radii)
associated with the relatively low-mass haloes that host the nominal central
galaxies in the analysis. A mock catalogue constructed from a recent
semi-analytic model shows very similar conformity effects to the data when
analysed in the same way, suggesting that there is no need to introduce new
physical processes to explain galactic conformity on 4 Mpc scales.
