We report on ALMA observations of D1, a system at z ∼ 6.15 with stellar mass M*~10^7 Msun 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 data set, 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 4σ tentative detection of [C II] emission with intrinsic luminosity L[CII]=(2.9 +-1.9) 10^6 Lsun, 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 [C II] 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 3σ upper limit values as low as ∼ a few 10^4 Msun, consistent with the values measured in local metal-poor galaxies.
Constraints on the [CII] luminosity of a proto-globular cluster at z ∼ 6 obtained with ALMA
Piero Rosati;
2021
Abstract
We report on ALMA observations of D1, a system at z ∼ 6.15 with stellar mass M*~10^7 Msun 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 data set, 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 4σ tentative detection of [C II] emission with intrinsic luminosity L[CII]=(2.9 +-1.9) 10^6 Lsun, 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 [C II] 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 3σ upper limit values as low as ∼ a few 10^4 Msun, consistent with the values measured in local metal-poor galaxies.File | Dimensione | Formato | |
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