Submillimetre galaxies in cosmological hydrodynamical simulations — an opportunity for constraining feedback models. (arXiv:2007.01885v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Hayward_C/0/1/0/all/0/1">Christopher C. Hayward</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sparre_M/0/1/0/all/0/1">Martin Sparre</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chapman_S/0/1/0/all/0/1">Scott C. Chapman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hernquist_L/0/1/0/all/0/1">Lars Hernquist</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nelson_D/0/1/0/all/0/1">Dylan Nelson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pakmor_R/0/1/0/all/0/1">R&#xfc;diger Pakmor</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pillepich_A/0/1/0/all/0/1">Annalisa Pillepich</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Springel_V/0/1/0/all/0/1">Volker Springel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Torrey_P/0/1/0/all/0/1">Paul Torrey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vogelsberger_M/0/1/0/all/0/1">Mark Vogelsberger</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Weinberger_R/0/1/0/all/0/1">Rainer Weinberger</a>

Submillimetre galaxies (SMGs) have long posed a challenge for theorists, and
self-consistently reproducing the properties of the SMG population in a
large-volume cosmological hydrodynamical simulation has not yet been achieved.
In this work, we employ a relatively simple method based on previous work to
predict the submm flux densities of simulated SMGs drawn from cosmological
simulations from the Illustris and IllustrisTNG projects and compare the
predicted number counts with observations. We find that the predicted SMG
number counts based on IllustrisTNG are significantly less than observed (more
than 1 dex at $S_{850} gtrsim 4$ mJy). The simulation from the original
Illustris project yields more SMGs than IllustrisTNG: the predicted counts are
consistent with those observed at both $S_{850} lesssim 5$ mJy and $S_{850}
gtrsim 9$ mJy and only a factor of $sim 2$ lower than observed at
intermediate flux densities. We demonstrate that IllustrisTNG hosts fewer SMGs
than Illustris because in the former, high-mass ($M_{star} sim 10^{11} ,
{rm M}_{odot}$) $z sim 2-3$ galaxies have lower dust masses and star
formation rates (SFRs) than in Illustris owing to differences in the sub-grid
models for stellar or/and active galactic nucleus (AGN) feedback between the
two simulations (we unfortunately cannot isolate the specific cause(s) post
hoc). Our results demonstrate that because our method enables predicting SMG
number counts in post-processing with a negligible computational expense, SMGs
can provide useful constraints for tuning sub-grid models in future
large-volume cosmological simulations. Higher resolution, which would lead to
stronger SFR enhancements in starbursts, could at least partially reconcile the
discrepancy between the IllustrisTNG SMG number counts and those observed.

Submillimetre galaxies (SMGs) have long posed a challenge for theorists, and
self-consistently reproducing the properties of the SMG population in a
large-volume cosmological hydrodynamical simulation has not yet been achieved.
In this work, we employ a relatively simple method based on previous work to
predict the submm flux densities of simulated SMGs drawn from cosmological
simulations from the Illustris and IllustrisTNG projects and compare the
predicted number counts with observations. We find that the predicted SMG
number counts based on IllustrisTNG are significantly less than observed (more
than 1 dex at $S_{850} gtrsim 4$ mJy). The simulation from the original
Illustris project yields more SMGs than IllustrisTNG: the predicted counts are
consistent with those observed at both $S_{850} lesssim 5$ mJy and $S_{850}
gtrsim 9$ mJy and only a factor of $sim 2$ lower than observed at
intermediate flux densities. We demonstrate that IllustrisTNG hosts fewer SMGs
than Illustris because in the former, high-mass ($M_{star} sim 10^{11} ,
{rm M}_{odot}$) $z sim 2-3$ galaxies have lower dust masses and star
formation rates (SFRs) than in Illustris owing to differences in the sub-grid
models for stellar or/and active galactic nucleus (AGN) feedback between the
two simulations (we unfortunately cannot isolate the specific cause(s) post
hoc). Our results demonstrate that because our method enables predicting SMG
number counts in post-processing with a negligible computational expense, SMGs
can provide useful constraints for tuning sub-grid models in future
large-volume cosmological simulations. Higher resolution, which would lead to
stronger SFR enhancements in starbursts, could at least partially reconcile the
discrepancy between the IllustrisTNG SMG number counts and those observed.

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