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Register a new userThe Nature of Sub-millimetre Galaxies in Cosmological Hydrodynamic Simulations
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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.
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What type of objects are being detected as $zsim 3$ Lyman break galaxies? Are they predominantly the most massive galaxies at that epoch, or are many of them smaller galaxies undergoing a short-lived burst of merger-induced star formation? We attempt to address this question using high-resolution cosmological hydrodynamic simulations including star formation and feedback. Our $Lambda$CDM simulation, together with Bruzual-Charlot population synthesis models, reproduces the observed number density and luminosity function of Lyman break galaxies when dust is incorporated. The inclusion of dust is crucial for this agreement. In our simulation, these galaxies are predominantly the most massive objects at this epoch, and have a significant population of older stars. Nevertheless, it is possible that our simulations lack the resolution and requisite physics to produce starbursts, despite having a physical resolution of $la 700$ pc at z=3. Thus we cannot rule out merger-induced starburst galaxies also contributing to the observed population of high-redshift objects.
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