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

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 2...

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Published in:arXiv.org 2023-06
Main Authors: Pope, Alexandra, McKinney, Jed, Kamieneski, Patrick, Battisti, Andrew, Aretxaga, Itziar, Brammer, Gabriel, Diego, Jose M, Hughes, David H, Keller, Erica, Marchesini, Danilo, Mizener, Andrew, Montana, Alfredo, Murphy, Eric, Whitaker, Katherine E, Wilson, Grant, Yun, Min
Format: Article
Language:English
Subjects:
Cosmic dust
Disk galaxies
Dust
Galactic evolution
Interstellar matter
Red shift
Rotating disks
Star & galaxy formation
Star formation rate
Stars & galaxies
Stellar mass
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Summary: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.
ISSN:2331-8422
DOI:10.48550/arxiv.2306.10450