A unique galaxy at z = 2.2, zC406690, has a striking clumpy large-scale ring structure that persists from rest UV to near-infrared, yet has an ordered rotation and lies on the star-formation main sequence. We combine new JWST/NIRCam and ALMA band 4 observations, together with previous VLT/SINFONI integral field spectroscopy and HST imaging to re-examine its nature. The high-resolution Hα kinematics are best fitted if the mass is distributed within a ring with total mass Mring=2×1010M⊙ and radius Rring = 4.6 kpc, together with a central undetected mass component (e.g., a "bulge") with a dynamical mass of Mbulge=8×1010M⊙. We also consider a purely flux emitting ring superposed over a faint exponential disk, or a highly "cuspy" dark matter halo, both disfavored against a massive ring model. The low-resolution CO(4-3) line and 142GHz continuum emission imply a total molecular and dust gas masses of Mmol,gas=7.1×1010M⊙ and Mdust=3×108M⊙ over the entire galaxy, giving a dust-to-mass ratio of 0.7%. We estimate that roughly half the gas and dust mass lie inside the ring, and that ∼10% of the total dust is in a foreground screen that attenuates the stellar light of the bulge in the rest-UV to near-infrared. Sensitive high-resolution ALMA observations will be essential to confirm this scenario and study the gas and dust distribution.
@article{arxiv.2503.00839,
title = {A large-scale ring galaxy at z = 2.2 revealed by JWST/NIRCam: kinematic observations and analytical modelling},
author = {A. Nestor Shachar and A. Sternberg and R. Genzel and D. Liu and S. H. Price and C. Pulsoni and L. J. Tacconi and R. Herrera-Camus and N. M. Forster Schreiber and A. Burkert and J. B. Jolly and D. Lutz and S. Wuyts and C. Barfety and Y. Cao and J. Chen and R. Davies and F. Eisenhauer and J. M. Espejo Salcedo and L. L. Lee and M. Lee and T. Naab and S. Pastras and T. T. Shimizu and E. Sturm and G. Tozzi and H. Ubler},
journal= {arXiv preprint arXiv:2503.00839},
year = {2025}
}