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 \simeq 6 - 12 .
The galaxies are followed in a rare , heavily overdense region within a \sim 5 \sigma density peak , which can host high- z quasars , and in an average density region , down to the stellar mass of M _ { star } \sim 4 \times 10 ^ { 7 } { M _ { \odot } } .
We find that the overdense regions evolve at a substantially accelerated pace — the most massive galaxy has grown to M _ { star } \sim 8.4 \times 10 ^ { 10 } { M _ { \odot } } by z = 6.3 , contains dust of M _ { dust } \sim 4.1 \times 10 ^ { 8 } { M _ { \odot } } , and is associated with a very high star formation rate , SFR \sim 745 M _ { \odot } ~ { } yr ^ { -1 } .
The attained SFR - M _ { star } correlation results in the specific SFR slowly increasing with M _ { star } .
Most of the UV radiation in massive galaxies is absorbed by the dust , its escape fraction f _ { esc } 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 L _ { IR } \sim 3.7 \times 10 ^ { 12 } { L _ { \odot } } at z = 6.3 , while L _ { IR } < 10 ^ { 11 } { L _ { \odot } } for the low-mass galaxies .
Therefore , ALMA can probe massive galaxies in the overdense region up to z \sim 10 with a reasonable integration time .
The UV spectral properties of disky 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 ( SMG ) 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 .