Dust Grain Growth at High Redshift: Starburst-driven CMB-Dark Supershells

TL;DR

This paper proposes a new mechanism where starburst-driven supershells in high-redshift galaxies can facilitate dust grain growth by trapping radiation, potentially explaining rapid dust accumulation in early galaxies.

Contribution

It introduces a semi-analytic model showing how supershells can enable dust growth at high redshift, a novel process not previously considered.

Findings

Supershells can become optically thick to starlight and CMB radiation.

Dust mass can increase by up to 10^6 solar masses in certain galaxies.

Mechanism operates in massive molecular clouds with high metallicity and density.

Abstract

We present a novel scenario for the growth of dust grains in galaxies at high-redshift ($z\sim 6$). In our model, the mechanical feedback from massive star clusters evolving within high-density pre-enriched media allows to pile-up a large amount of matter into massive supershells. If the gas metallicity ($\geq$ Z$_{\odot}$), number density ($\geq 10^6$ cm$^{-3}$) and dust-to-gas mass ratio ($\sim 1/150 \times Z$) within the supershell are sufficiently large, such supershells may become optically thick to the starlight emerging from their host star clusters and even to radiation from the Cosmic Microwave Background (CMB). Based on semi-analytic models, we argue that this mechanism, occurring in the case of massive ($\geq 10^7$ M$_{\odot}$) molecular clouds hosting $\geq 10^6$ M$_{\odot}$ star clusters, allows a large mass of gas and dust to acquire a temperature below that of the CMB, whereupon dust grain growth may occur with ease. In galaxies with total stellar mass $M_{*}$, grain growth within supershells may increase the dust mass by $\sim 10^6$ M$_{\odot}$ $(M_{*}/10^{8}$ M$_{\odot}$).