New constraints on the molecular gas content of a z ∼ 8 galaxy from JVLA CO(J=2-1) observations

As the primary fuel for star formation, molecular gas plays a key role in galaxy evolution. A number of techniques have been used for deriving the mass of molecular reservoirs in the early Universe (e.g. [C II]158 mu m, [C I], dust continuum), but the standard approach of CO-based estimates has been limited to a small number of galaxies due to the intrinsic faintness of the line. We present Jansky Very Large Array observations of the galaxy MACS0416_Y1, targeting CO(2-1) and rest-frame radio continuum emission, which result in upper limits on both quantities. Adding our continuum limit to the published far-infrared (FIR) spectral energy distribution, we find a small non-thermal contribution to the FIR emission, a low-dust mass (log(10)(M-D/M-circle dot) similar to 5), and an abnormally high-dust temperature (T-D greater than or similar to 90 K) that may indicate a recent starburst. Assuming a low metallicity (Z/Z(circle dot) similar to 0.25), we find evidence for M-H2, CO less than or similar to 10(10) M-circle dot, in agreement with previous [C II] investigations (M-H2, [C II] similar to 10(9.6) M-circle dot). Upcoming JWST observations of this source will result in a precise determination of Z, enabling better constraints and an unprecedented view of the gaseous reservoir in this primordial starburst galaxy.