An Edge-on Regular Disk Galaxy at z=5.289

Abstract: While rotation-supported gas disks are known to exist as early as at z ~ 7, it is still a general belief that stellar disks form late in the Universe. This picture is now being challenged by the observations from the James Webb Space Telescope (JWST), which have revealed a large number of disk-like galaxies that could be at z > 3, with some being candidates at z > 7. As an early formation of stellar disks will greatly impact our theory of galaxy formation and evolution, it is important to determine when such systems first emerged. Here we present D-CEERS-RUBIES-z5289 at z=5.289+-0.001, the second confirmed stellar disk at z > 5, discovered using the archival JWST NIRCam imaging and NIRSpec spectroscopic data. This galaxy has a highly regular edge-on disk morphology, extends to ~6.2 kpc along its major axis, and has an effective radius of ~1.3--1.4 kpc. Such a large stellar disk is yet to be produced in numerical simulations. By analyzing its 10-band spectral energy distribution using four different tools, we find that it has a high stellar mass of 10^{9.5-10.0} M_sun. Its age is in the range of 330--510 Myr, and it has a mild star formation rate of 10--30 M_sun/yr. While the current spectroscopic data do not allow the derivation of its rotation curve, the width of its Halpha line from the partial slit coverage on one side of the disk reaches ~345 km/s, which suggests that it could have a significant contribution from rotation.