Reproducing sub-millimetre galaxy number counts with cosmological hydrodynamic simulations

Abstract

Matching the number counts of high-z sub-millimetre-selected galaxies (SMGs) has been a long standing problem for galaxy formation models. In this paper, we use 3D dust radiative transfer to model the sub-mm emission from galaxies in the Simba cosmological hydrodynamic simulations, and compare predictions to the latest singledish observational constraints on the abundance of 850 µm-selected sources. We find unprecedented agreement with the integrated 850 µm luminosity function, along with good agreement in the redshift distribution of bright SMGs. The excellent agreement is driven primarily by Simba's good match to infrared measures of the star formation rate (SFR) function between z = 2 − 4 at high SFRs. Also important is the self-consistent on-the-fly dust model in Simba, which predicts, on average, higher dust masses (by up to a factor of 7) compared to using a fixed dust-to-metals ratio of 0.3. We construct a lightcone to investigate the effect of far-field blending, and find minimal contribution to the shape and normalisation of the luminosity function. We provide new fits to the 850 µm luminosity as a function of SFR and dust mass. Our results demonstrate that exotic solutions to the discrepancy between sub-mm counts in simulations and observations, such as a top-heavy IMF, are unnecessary, and that sub-millimetre-bright phases are a natural consequence of massive galaxy evolution.

The Complete Redshift Distribution of Dusty Star-forming Galaxies from the SPT-SZ Survey

“…Based on models of the high-redshift DSFG population (e.g., Baugh et al 2005;Lacey et al 2010;Béthermin et al 2012bBéthermin et al , 2017Hayward et al 2013;Lagos et al 2019;Lovell et al 2020), very few sources would be intrinsically bright The offset in apparent L FIR between the lensed (SPT) and unlensed (ALESS) sources is due to gravitational magnification. It should be noted that for many of the ALESS sources, the photometry is not well constrained, which is reflected in the size of the associated error bars.…”

“…3 , but this number should be used with caution, as it is based upon just one source (Marrone et al 2018). To place this number in context, we compare with other observations (Coppin et al 2009;Ivison et al 2016;Cooke et al 2018) and theoretical predictions (Hayward et al 2013;Béthermin et al 2017;Lagos et al 2019;Lovell et al 2020) in Table 2 and Figure 16. The stated number densities are taken to have an upper limit of z=8 and the errors are again calculated using the statistical errors from both the SPT and ALESS surveys in quadrature.…”

“…Lovell et al (2020) modeled the m S 850 m emission using a full radiative transfer code coupled with a full cosmological lightcone. To compare with our model we have selected sources The model is in good agreement with the SPT measurement at z∼6, but overpredicts the density of sources at z∼4.…”

Mapping Obscuration to Reionization with ALMA (MORA): 2mm Efficiently Selects the Highest-Redshift Obscured Galaxies

“…Lastly, we compare to the empirical model predictions for the submillimeter sky presented by Casey et al (2018b,a) and expanded on in Zavala et al (2018a) 12 Software: ProSpect (Robotham et al 2020) 13 See also Lovell et al (2020) and Hayward et al (2021) for similar analysis using the Simba and Illustris-TNG hydrodynamical simulations from Davé et al 2019 and, finally, in Z21. The key difference between the Casey et al (2018b) models and the cosmological semiempirical models is the built-in flexibility to test different hypothetical evolving infrared luminosity functions against data.…”

A Long Stream of Metal-Poor Cool Gas around a Massive Starburst Galaxy at z = 2.67

“…Attempting to reduce this tension between observations and theory, more recent cosmological zoom-in simulations have implemented recipes of stronger and presumably more realistic stellar feedback, which manages to preserve cool gas reservoirs in the accreted sub-halos during earlier phases of star formation before their infall into the massive halo. The presence of these gas-rich sub-halos increases the cool gas covering factor around QSOs (Faucher-Giguère et al 2016) and their prolonged bombardment to the central galaxy leads to a rising star formation history that eventually produces SMGs between 2 < z < 3 (Narayanan et al 2015;Lovell et al 2020).…”