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arXiv · 2306.10450

ALMA reveals a stable rotating gas disk in a paradoxical low-mass, ultra-dusty galaxy at z = 4.274

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 Montana·Eric Murphy·Katherine E. Whitaker·Grant Wilson·Min Yun
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Abstract

We report ALMA detections of [CII] and dust continuum in Az9, a multiply-imaged galaxy behind the Frontier Field cluster MACSJ0717.5+3745. The bright [CII] emission line provides a spectroscopic redshift of z = 4.274. This strongly lensed (mu = 7 +/- 1) galaxy has an intrinsic stellar mass of only 2e9 Msun and a total star formation rate of 26 Msun/yr (~80% of which is dust obscured). Using public magnification maps, we reconstruct the [CII] emission in the source plane to reveal a stable, rotation-dominated disk with V/sigma = 5.3, which is > 2x higher than predicted from simulations for similarly high-redshift, low-mass galaxies. In the source plane, the [CII] 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 [CII]; L[CII]/LIR = 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 dust continuum and [CII], Az9 is an excellent laboratory in which to study early dust enrichment in the interstellar medium.

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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 Montana, Eric Murphy, Katherine E. Whitaker, Grant Wilson, Min Yun. 2023-06-18. ALMA reveals a stable rotating gas disk in a paradoxical low-mass, ultra-dusty galaxy at z = 4.274. https://doi.org/10.3847/2041-8213%2Facdf5a

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