ALMA Reveals a Stable Rotating Gas Disk in a Paradoxical Low-mass, Ultradusty Galaxy at z = 4.274

Autor: Alexandra Pope, Jed McKinney, Patrick Kamieneski, Andrew Battisti, Itziar Aretxaga, Gabriel Brammer, Jose M. Diego, David H. Hughes, Erica Keller, Danilo Marchesini, Andrew Mizener, Alfredo Montaña, Eric Murphy, Katherine E. Whitaker, Grant Wilson, Min Yun
Jazyk: angličtina
Rok vydání: 2023
Předmět:
Zdroj: The Astrophysical Journal Letters, Vol 951, Iss 2, p L46 (2023)
Druh dokumentu: article
ISSN: 2041-8213
2041-8205
DOI: 10.3847/2041-8213/acdf5a
Popis: We report ALMA detections of [C ii ] and a dust continuum in Az9, a multiply imaged galaxy behind the Frontier Field cluster MACS J0717.5+3745. The bright [C ii ] emission line provides a spectroscopic redshift of z = 4.274. This strongly lensed ( μ = 7 ± 1) galaxy has an intrinsic stellar mass of only 2 × 10 ^9 M _⊙ and a total star formation rate of 26 M _⊙ yr ^−1 (∼80% of which is dust-obscured). Using public magnification maps, we reconstruct the [C ii ] emission in the source plane to reveal a stable, rotation-dominated disk with V / σ = 5.3, which is >2× higher than predicted from simulations for similarly high-redshift, low-mass galaxies. In the source plane, the [C ii ] disk has a half-light radius of 1.8 kpc and, along with the dust, is spatially offset from the peak of the stellar light by 1.4 kpc. Az9 is not deficient in [C ii ]; L _[C _II _] / L _IR = 0.0027, consistent with local and high-redshift normal star-forming galaxies. While dust-obscured star formation is expected to dominate in higher-mass galaxies, such a large reservoir of dust and gas in a lower-mass disk galaxy 1.4 Gyr after the Big Bang challenges our picture of early galaxy evolution. Furthermore, the prevalence of such low-mass dusty galaxies has important implications for the selection of the highest-redshift dropout galaxies with JWST. As one of the lowest stellar mass galaxies at z > 4 to be detected in a dust continuum and [C ii ], Az9 is an excellent laboratory in which to study early dust enrichment in the interstellar medium.
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