2024/05/07 by Andrew Mizener, Alexandra Pope, Mizener, Andrew +11
Physics and Astronomy · #Adaptive optics and wavefront sensing #Astronomy and Astrophysical Research #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2405.04582
openalex publication_date 2024/05/07 · openalex created_date 2024/05/11 · openalex updated_date 2026/07/28
We present the molecular gas content and ISM conditions of MACSJ0717 Az9, a strong gravitationally lensed z=4.273, M* ≃ 2×109M\odot star-forming galaxy with an unusually high (∼ 80%) obscured star formation fraction. We detect CO(4-3) in two independent lensed images, as well as [N II]205μm, with ALMA. We derive a molecular gas mass of log10[M_H2 (M\odot)] = 9.77 making it moderately deficient in molecular gas compared to the lower redshift gas fraction scaling relation. Leveraging photodissociation region (PDR) models, we combine our CO(4-3) measurements with existing measurements of the [C II] 158μm line and total infrared luminosity to model the PDR conditions. We find PDR conditions similar to local star-forming galaxies, with a mean hydrogen density log10[nH cm-3] = 4.80±0.39 and a mean radiation field strength log10[G0 Habing] = 2.83±0.26. Based on Band 3 continuum data, we derive an upper limit on the intrinsic dust mass of log10[M\rm dust (M\odot)] < 7.73, consistent with existing estimates. We use the 3D tilted-ring model fitting code 3D-Barolo to determine the kinematic properties of the CO(4-3) emitting gas. We find that it is rotationally dominated, with a V/σ=4.6 ± 1.7, consistent with the kinematics of the [C II]. With PDR conditions remarkably similar to normal dusty star-forming galaxies at z ~ 0.2 and a stable molecular disk, our observations of Az9 suggest that the dust-obscured phase for a low-mass galaxy at z∼4 is relatively long. Thus, Az9 may be representative of a more widespread population that has been missed due to insufficiently deep existing millimeter surveys.