REBELS-25: Discovery of a dynamically cold disc galaxy at z = 7.31

Rowland, LE, Hodge, J, Bouwens, R, Piña, PEM, Hygate, A, Algera, H, Aravena, M, Bowler, R, Da Cunha, E, Dayal, P, Ferrara, A, Herard-Demanche, T, Inami, H, Van Leeuwen, I, De Looze, I, Oesch, P, Pallottini, A, Phillips, S ORCID: 0000-0003-4652-1090, Rybak, M, Schouws, S et al (2024) REBELS-25: Discovery of a dynamically cold disc galaxy at z = 7.31. Monthly Notices of the Royal Astronomical Society, 535 (3). pp. 2068-2091. ISSN 0035-8711

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Abstract

We present high-resolution (∼ 0.14 arcsec = 710 pc) Atacama Large Millimetre/submillimetre Array [C II] 158 μm and dust continuum follow-up observations of REBELS-25, a [C II]-luminous (L[CII] = (1.7 ± 0.2) × 109 L) galaxy at redshift z = 7.3065 ± 0.0001. These high-resolution, high signal-to-noise observations allow us to study the sub-kpc morphology and kinematics of this massive (M∗ = 8+4−2 × 109M) star-forming (SFRUV+IR = 199+101−63 Myr−1) galaxy in the Epoch of Reionization. By modelling the kinematics with 3DBAROLO, we find it has a low-velocity dispersion (σ¯ = 33+9−7 km s−1) and a high ratio of ordered-to-random motion (Vrot, max/σ¯ = 11+6−5), indicating that REBELS-25 is a dynamically cold disc. Additionally, we find that the [C II] distribution is well fit by a near-exponential disc model, with a Sersic ´ index, n, of 1.3 ± 0.2, and we see tentative evidence of more complex non-axisymmetric structures suggestive of a bar in the [C II] and dust continuum emission. By comparing to other high spatial resolution cold gas kinematic studies, we find that dynamically cold discs seem to be more common in the high-redshift Universe than expected based on prevailing galaxy formation theories, which typically predict more turbulent and dispersion-dominated galaxies in the early Universe as an outcome of merger activity, gas accretion, and more intense feedback. This higher degree of rotational support seems instead to be consistent with recent cosmological simulations that have highlighted the contrast between cold and warm ionized gas tracers, particularly for massive galaxies. We therefore show that dynamically settled disc galaxies can form as early as 700 Myr after the big bang

Item Type:	Article
Uncontrolled Keywords:	galaxies: evolution; galaxies: high-redshift; galaxies: kinematics and dynamics; 5101 Astronomical Sciences; 51 Physical Sciences; 5109 Space Sciences; 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Date of acceptance:	20 September 2024
Date of first compliant Open Access:	1 June 2026
Date Deposited:	01 Jun 2026 15:11
Last Modified:	01 Jun 2026 15:11
DOI or ID number:	10.1093/mnras/stae2217
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28699

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