How much gas and dust is in the z=5.7 Lyman-break galaxy HZ10? ALMA Bands 10 to 4 and JWST/NIRSpec study of its interstellar medium

Abstract

A complete overview of the stellar, gas and dust contents of galaxies is key to understanding their assembly at early times. However, an estimation of molecular and atomic gas reservoirs at high redshift relies on various indirect tracers, while robust dust mass measurements require multiband far-infrared continuum observations. We present a census of the full baryonic content of the main sequence star-forming galaxy HZ10 at z=5.65, a unique case study where all the necessary tracers are available. We used new ALMA Band 10 (λ_ ̊m rest m ) and Band 4 ( observations toward HZ10, combined with data previously taken in ALMA Bands 6 through 9 (approx70 - 200,μ ) to constrain its dust properties. We complete the baryonic picture using archival high-resolution observations that provide both a dynamical mass and molecular and atomic gas mass estimates, a JVLA CO(2-1)-based molecular gas mass, and JWST metallicity and stellar mass measurements. m We detected continuum emission from HZ10 in Bands 10 and 4 at the 3.4-4.0σ level. We measured a dust temperature of T_ = 37_ dust -5 ^ +6 ,K and dust mass of łog(M_ /M_⊙) = 8.0 ± 0.1. By leveraging the dynamical constraints, we were able to infer its total gas budget. We find that commonly used -to-H_2 and -to-HI conversions might overpredict the gas mass relative to the dynamical mass. For this reason, we derived a -to-total-ISM mass (atomic + molecular) conversion factor. For HZ10, this corresponds to α_ dust ̊m CII ^ ̊m ISM = 38^ +28 _ -26 M_⊙ L_⊙^ -1 . We also found that HZ10 falls below the local scaling relation between the dust-to-gas ratio and metallicity, suggesting inefficient ISM dust growth. These results demonstrate a powerful synergy between ALMA and JWST in disentangling the baryonic components of early galaxies, paving the way for future studies of larger samples to dynamically calibrate -to-gas mass conversion factors and further unravel the pathways of early dust buildup.