A massive barred spiral galaxy at z = 5.102 discovered by JWST

Abstract

We report M1149-BSG-z5, a barred spiral galaxy at $z=5.102$, identified in the parallel field of MACS J1149+2223 with JWST and HST. M1149-BSG-z5 is the highest redshift barred galaxy candidate to date. Both isophote ellipse fitting and structural modeling support a stellar bar of length $a_{\mathrm{bar}}\approx 4.5$ kpc, and extended spiral arms peaking at $r\approx 5.5$ kpc. M1149-BSG-z5 is a massive main sequence star-forming galaxy, with a stellar mass of $10^{10.45}{\mathrm{M}}_{\odot }$ and a star-formation rate of $144{\mathrm{M}}_{\odot }/yr$. A concentrated bulge is embedded in an extended disk with a global Sérsic index $n=2.37$. With an effective radius of $R_e=2.61\mathrm{kpc}$, M1149-BSG-z5 is larger than typical galaxies at $z\sim 5$ and comparable to barred galaxies at $2<z<4$. M1149-BSG-z5 also hosts a broad-line AGN, with a relatively low black-hole-to-stellar mass ratio of ${\mathrm{M}}_{\mathrm{BH}}/{\mathrm{M}}_{\ast }\sim 10^{-3}$. Its metal-enriched emission-line properties indicate that it is already chemically evolved. These properties imply M1149-BSG-z5 as an early-assembled and structurally evolved galaxy. We also find that M1149-BSG-z5 resides in an overdense region with a nearby companion galaxy, suggesting an interaction-driven bar formation mechanism. Its concentrated light, early assembly and main-sequence star formation also suggest baryon-dominated, gas-rich conditions, where gravitational instability can further accelerate the bar formation.

17 pages, 8 figures