Constraints on the [CII] luminosity of a proto-globular cluster at z~6 obtained with ALMA

TL;DR

This study uses ALMA to observe a proto-globular cluster at z~6, providing the first direct insights into its neutral gas properties and [CII] emission, revealing a possible deficiency linked to low metallicity and intense feedback.

Contribution

First direct measurement of [CII] emission in a high-redshift globular cluster progenitor, exploring its gas properties and star formation relation.

Findings

Tentative detection of faint [CII] emission at z~6.15

[CII] luminosity is among the lowest at high redshift

Indicates possible gas deficiency due to low metallicity and feedback

Abstract

We report on ALMA observations of D1, a system at z~6.15 with stellar mass M_* ~ 10^7 M_sun containing globular cluster (GC) precursors, strongly magnified by the galaxy cluster MACS J0416.1-2403. Since the discovery of GC progenitors at high redshift, ours is the first attempt to probe directly the physical properties of their neutral gas through infrared observations. A careful analysis of our dataset, performed with a suitable procedure designed to identify faint narrow lines and which can test various possible values for the unknown linewidth value, allowed us to identify a 4-sigma tentative detection of [CII] emission with intrinsic luminosity L_CII=(2.9 +/- 1.4) 10^6 L_sun, one of the lowest values ever detected at high redshift. This study offers a first insight on previously uncharted regions of the L_CII-SFR relation. Despite large uncertainties affecting our measure of the star formation rate, if taken at face value our estimate lies more than 1 dex below the values observed in local and high redshift systems. Our weak detection indicates a deficiency of [CII] emission, possibly ascribed to various explanations, such as a low-density gas and/or a strong radiation field caused by intense stellar feedback, and a low metal content. From the non-detection in the continuum we derive constraints on the dust mass, with 3-sigma upper limit values as low as a few 10^4 M_sun, consistent with the values measured in local metal-poor galaxies.