The dust mass in z > 6 normal star forming galaxies

TL;DR

This study models dust accumulation in early galaxies at z > 6, revealing that grain growth in metal-enriched environments dominates dust mass, especially in larger galaxies, aligning with recent ALMA observations.

Contribution

It introduces a semi-numerical approach combining hydrodynamical simulations with chemical evolution models to explain dust mass origins in high-redshift galaxies.

Findings

Grain growth dominates dust mass in galaxies with Mstar > 10^9 Msun.

Supernovae alone cannot account for observed dust masses, requiring efficient grain growth.

High-density conditions are necessary for grain growth, similar to those in QSO host galaxies.

Abstract

We interpret recent ALMA observations of z > 6 normal star forming galaxies by means of a semi-numerical method, which couples the output of a cosmological hydrodynamical simulation with a chemical evolution model which accounts for the contribution to dust enrichment from supernovae, asymptotic giant branch stars and grain growth in the interstellar medium. We find that while stellar sources dominate the dust mass of small galaxies, the higher level of metal enrichment experienced by galaxies with Mstar > 10^9 Msun allows efficient grain growth, which provides the dominant contribution to the dust mass. Even assuming maximally efficient supernova dust production, the observed dust mass of the z = 7.5 galaxy A1689-zD1 requires very efficient grain growth. This, in turn, implies that in this galaxy the average density of the cold and dense gas, where grain growth occurs, is comparable to that inferred from observations of QSO host galaxies at similar redshifts. Although plausible, the upper limits on the dust continuum emission of galaxies at 6.5 < z < 7.5 show that these conditions must not apply to the bulk of the high redshift galaxy population