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

Abstract

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 × 109 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.

GA-NIFS: Early-stage feedback in a heavily obscured active galactic nucleus at z = 4.76

“…On one hand, a large number of kinematic studies at 1 < z < 4 suggest that high redshift galaxies are more turbulent than local ones (Cresci et al 2009;Förster Schreiber et al 2009Epinat et al 2010;Gnerucci et al 2011;Ianjamasimanana et al 2012;Green et al 2014;Wisnioski et al 2015;Mogotsi et al 2016;Di Teodoro et al 2016;Harrison et al 2017;Swinbank et al 2017;Turner et al 2017;Johnson et al 2018;Übler et al 2019;Girard et al 2021) with V/σ reaching values close to unity at z ∼ 3.5. On the other hand, the results from kinematic studies at z > 4 lead to contrasting results showing the presence of both turbulent (Tsukui & Iguchi 2021;Herrera-Camus et al 2023;Parlanti et al 2023;de Graaff et al 2024) and kinematically cold galaxies (Sharda et al 2019;Neeleman et al 2020;Rizzo et al 2020Rizzo et al , 2021Jones et al 2021;Fraternali et al 2021;Lelli et al 2021;Posses et al 2023;Pope et al 2023) with values of V/σ ranging from 20 to 0.1 across the redshift range 4 < z < 8. However, we note that results at high redshift are limited either by small sample sizes for galaxies observed with high angular resolution or by significant uncertainties due to the low angular resolution observations used for the larger samples of galaxies.…”

Hidden Giants in JWST's PEARLS: An Ultramassive z = 4.26 Submillimeter Galaxy that Is Invisible to HST

“…These parameters would imply a galaxy more similar to 850.2 in its physical properties, but we believe that this poor fit was erroneous due to the distinct low and high extinction regions that were being modeled with a single dust extinction term. Similar model biases may also be responsible for some apparently low-mass SMGs identified from SED fitting of systems with a wide range in A V (e.g., Pope et al 2023). This erroneous fit also produces an apparent power-law-like excess in the observed fluxes longward of 3.6 μm compared to the model.…”

“…Ikarashi et al 2023, in preparation). After accounting for lensing magnification, Figure 7(a) shows that 850.1 and 850.2 lie at either end of the mass range seen in 850 μmselected galaxies at z > 4: 850.1 being one of the more massive galaxies found (from dust-selected samples or other methods) at these redshifts (see also, Casey et al 2019), while 850.2 is one of the least massive in dust-selected samples (see also, Pope et al 2023). Looking at their specific SFR, 850.1 lies below and 850.2 lies just inside the claimed "starburst" regime at this redshift.…”

The Galaxies Missed by Hubble and ALMA: The Contribution of Extremely Red Galaxies to the Cosmic Census at 3 < z < 8

“…It is also in part because of the large uncertainty in the abundance of more common, but less extreme galaxies, that are below the detection limits of typical multiwavelength surveys (and difficulties in determining their counterparts and redshifts; e.g., Smail et al 2021). As the abundance of massive galaxies declines, less massive and fainter sources (e.g., Pope et al 2017Pope et al , 2023 could plausibly harbor an increasing fraction of the obscured star formation at early times. Progress has been made by identifying fainter, dusty galaxies with ever increasing Atacama Large Millimeter/submillimeter Array (ALMA) area (in particular using longer-wavelength, >2-3 mm selections to filter out lower-redshift sources; Béthermin et al 2015;Casey et al 2021;Cooper et al 2022).…”