The Nature of Sub-millimetre Galaxies in Cosmological Hydrodynamic Simulations

TL;DR

This paper uses cosmological hydrodynamic simulations to explore the properties and origins of sub-millimetre galaxies at redshift 2, providing insights into their formation, characteristics, and evolution.

Contribution

It presents a novel simulation-based model of SMGs that challenges merger-centric views, highlighting smooth gas infall and satellite accretion as key processes.

Findings

Simulated SMGs have stellar masses of log M*/Mo~11-11.7 and SFRs of 180-500 Mo/yr.

SMGs are typically located in ~10^13 Mo halos and evolve into brightest group galaxies by z=0.

Simulations match observed SMG properties as well as merger-based models, suggesting alternative formation scenarios.

Abstract

We study the nature of rapidly star-forming galaxies at z=2 in cosmological hydrodynamic simulations, and compare their properties to observations of sub-millimetre galaxies (SMGs). We identify simulated SMGs as the most rapidly star-forming systems that match the observed number density of SMGs. In our models, SMGs are massive galaxies sitting at the centres of large potential wells, being fed by smooth infall and gas-rich satellites at rates comparable to their star formation rates (SFR). They are not typically undergoing major mergers that significantly boost their quiescent SFR, but they still often show complex gas morphologies and kinematics. Our simulated SMGs have stellar masses of log M*/Mo~11-11.7, SFRs of ~180-500 Mo/yr, a clustering length of 10 Mpc/h, and solar metallicities. The SFRs are lower than those inferred from far-IR data by a factor of 3, which we suggest may owe to one or more systematic effects in the SFR calibrations. SMGs at z=2 live in ~10^13 Mo halos, and by z=0 they mostly end up as brightest group galaxies in ~10^14 Mo halos. We predict that higher-M* SMGs should have on average lower specific SFRs, less disturbed morphologies, and higher clustering. We also predict that deeper far-IR surveys will smoothly join SMGs onto the massive end of the SFR-M* relationship defined by lower-mass z=2 galaxies. Overall, our simulated rapid star-formers provide as good a match to available SMG data as merger-based scenarios, offering an alternative scenario that emerges naturally from cosmological simulations.