Dusty galaxies in the Epoch of Reionization: simulations

Abstract

The recent discovery of dusty galaxies well into the Epoch of Reionization (redshift z > 6) poses challenging questions about the properties of the interstellar medium in these pristine systems. By combining state-of-the-art hydrodynamic and dust radiative transfer simulations, we address these questions focusing on the recently discovered dusty galaxy A2744 YD4 (z = 8.38, Laporte et al. 2017). We show that we can reproduce the observed spectral energy distribution (SED) only using different physical values with respect to the inferred ones by Laporte et al. (2017), i.e. a star formation rate of SFR = 78 M yr −1 , a factor ≈ 4 higher than deduced from simple Spectral Energy Distribution fitting. In this case we find: (a) dust attenuation (corresponding to τ V = 1.4) is consistent with a Milky Way extinction curve; (b) the dust-to-metal ratio is low, f d ∼ 0.08, implying that early dust formation is rather inefficient; (c) the luminosity-weighted dust temperature is high, T d = 91 ± 23 K, as a result of the intense (≈ 100× MW) interstellar radiation field; (d) due to the high T d , the ALMA Band 7 detection can be explained by a limited dust mass, M d = 1.6 × 10 6 M . Finally, the high dust temperatures might solve the puzzling low infrared excess recently deduced for high-z galaxies from the IRX-β relation.

The absence of [C ii] 158 $\mu$m emission in spectroscopically confirmed galaxies at z > 8

“…Using MAGPHYS (da Cunha et al 2008), we can give a first constraint on the dust temperature in this object T dust > 55 K. This value contrasts with the value generally used to determine the dust properties at high-z (T∼30K), but is consistent with recent simulations (e.g. Behrens et al 2018) which predict a higher dust temperature at high redshifts. Using the 3σ upper limits for both band 5 and 6 observations decreases the minimum dust temperature to T>43 K.…”

Deep into the structure of the first galaxies: SERRA views

“…The average 13 radiation field is G = (7.9 ± 23.1) G0 i.e. compatible with the assumption in Pallottini et al (2017b), where G = G0(SFR/M yr −1 ) (see also Behrens et al 2018). Note that the variance of the radiation field is 3 times the mean, as in the MW (Habing 1968;Wolfire et al 2003).…”

High-redshift JWST predictions from IllustrisTNG: dust modelling and galaxy luminosity functions

“…Aoyama et al (2017) found that the assumption of fixed dust-tometal ratio is no longer valid once galaxies are older than 0.2 Gyr. Behrens et al (2018) found in simulations that the dust-to-metal ratios for galaxies at z ∼ 8 are only 0.08, i.e. far lower than the value in the local Universe.…”