Understanding the Sunyaev-Zeldovich decrement versus halo mass using the
  SIMBA and TNG Simulations
  The relation between the integrated Sunyaev-Zeldovich (SZ) $y$-decrement
versus halo mass ($Y$-$M$) can potentially constrain galaxy formation models,
if theoretical and observational systematics can be properly assessed. We
investigate the $Y-M$ relation in the SIMBA and IllustrisTNG-100 cosmological
hydrodynamic simulations, quantifying the effects of feedback, line-of-sight
projection, and beam convolution. We find that SIMBA's AGN jet feedback
generates strong deviations from self-similar expectations for the $Y-M$
relation, especially at $M_{500}<10^{13}M_{\odot}$. In SIMBA this is driven by
suppressed in-halo $y$ contributions owing to lowered halo baryon fractions.
IllustrisTNG results more closely resemble SIMBA without jets. Projection of
line-of-sight structures weakens these model differences slightly, but they
remain significant at mostly group and lower halo masses. In contrast, beam
smearing at $\textit{Planck}$ resolution makes the models indistinguishable,
and both models appear to agree well with $\textit{Planck}$ data down to the
lowest masses probed. We show that the arcminute resolution expected from
forthcoming facilities would retain the differences between model predictions,
and thereby provide strong constraints on AGN feedback.
