Observational properties of simulated galaxies in overdense and average regions at redshifts z ≃ 6-12

Abstract

We use high-resolution zoom-in cosmological simulations of galaxies of Romano-Díaz et al., post-processing them with a panchromatic three-dimensional radiation transfer code to obtain the galaxy UV luminosity function (LF) at z sime; 6-12. The galaxies are followed in a rare, heavily overdense region within a ~5σ density peak, which can host high-z quasars, and in an average density region, down to the stellar mass of Mstar ~ 4 × 107 M⊙. We find that the overdense regions evolve at a substantially accelerated pace - the most massive galaxy has grown to Mstar ~ 8.4 × 1010 M⊙ by z = 6.3, contains dust of Mdust ~ 4.1 × 108 M⊙, and is associated with a very high star formation rate, SFR ~ 745 M⊙ yr-1. The attained SFR-Mstar correlation results in the specific SFR slowly increasing with Mstar. Most of the UV radiation in massive galaxies is absorbed by the dust, its escape fraction fesc is low, increasing slowly with time. Galaxies in the average region have less dust, and agree with the observed UV LF. The LF of the overdense region is substantially higher, and contains much brighter galaxies. The massive galaxies are bright in the infrared (IR) due to the dust thermal emission, with LIR ~ 3.7 × 1012 L⊙ at z = 6.3, while LIR < 1011 L⊙ for the low-mass galaxies. Therefore, ALMA can probe massive galaxies in the overdense region up to z = 10 with a reasonable integration time. The UV spectral properties of discy galaxies depend significantly upon the viewing angle. The stellar and dust masses of the most massive galaxy in the overdense region are comparable to those of the sub-millimetre galaxy found by Riechers et al. at z = 6.3, while the modelled SFR and the sub-millimetre flux fall slightly below the observed one. Statistical significance of these similarities and differences will only become clear with the upcoming ALMA observations.