Barred Spiral Galaxy at z=5.102: A New Frontier of the Early Universe ✦
A barred spiral galaxy M1149-BSG-z5 at redshift z=5.102 has been discovered—the most distant known to date. Photometric analysis and structural modeling revealed a stellar bar ~4.5 kpc in length and spiral arms with a brightness peak at ~5.5 kpc. This is a massive galaxy (stellar mass 10^10.45 M_⊙) on the main sequence with a star formation rate of 144 M_⊙/yr, Sérsic index n=2.37, and effective radius 2.61 kpc, exceeding typical sizes at z~5. The nucleus hosts an active galactic nucleus with broad emission lines and a low mass ratio (M_BH/M_* ~ 10^-3). Emission lines indicate high metallicity. The galaxy is in an overdense environment with a close companion. Early bar formation was likely accelerated by tidal interaction in a gas-rich, baryon-dominated medium.
Context
Studying the evolution of galaxies in the early Universe is key to understanding how structures like our Milky Way form. Bars—elongated structures of stars and gas that redistribute momentum—are of particular interest and closely tied to star formation and secular evolution. According to observations by Edwin Hubble, who laid the foundations of extragalactic astronomy, and the law of cosmic expansion, distant objects are seen as they were billions of years ago. Until recently, however, bars were thought to appear only at later stages, when disks become dynamically cold. The discovery of a massive barred spiral galaxy at redshift z=5.102 with the James Webb Space Telescope challenges these views, pointing to the possibility of early formation of ordered structures.
Methods
Deep images from JWST and Hubble in a wide wavelength range were used to detect and analyze M1149-BSG-z5. Morphology was studied using photometry and spectroscopy: elliptical isophotometry, surface brightness modeling with Sersic profiles, and emission line analysis. The Doppler effect allowed accurate measurement of redshift and relative velocities. Data interpretation involved numerical simulations and modern stellar population models (CIGALE).
Results
The galaxy exhibits a clear bar about 4.5 kpc long and nascent spiral arms. It has a stellar mass of 10^10.45 M⊙, a star formation rate of 144 M⊙/year, and an effective radius of 2.61 kpc, significantly larger than typical galaxies at z~5. An active nucleus (AGN) with a black hole mass of ~10^7.5 M⊙, roughly 1000 times less than the bulge mass, was detected in the center. Spectra indicate high metallicity (~50% solar), pointing to rapid chemical evolution. The galaxy resides in a dense environment: a companion is nearby at 21.2 kpc with a similar redshift, and the field shows photometric overdensity, suggesting possible interaction.
Implications
This discovery implies that bars can form within the first billion years after the Big Bang. It challenges traditional disk evolution models and highlights the role of internal processes in the early Universe. The presence of an AGN and chemical maturity indicate rapid assembly and reprocessing of matter. A simple estimate using Newton's law of gravitation gives an orbital period of about 170 million years, comparable to the age of the bar's stellar population.
Future development
Future observations with high spatial resolution, such as with ALMA interferometers, are needed to confirm the bar's dynamic nature. Kinematic maps will verify whether the disk is truly cold and if baryonic mass dominates. Further modeling will help clarify the bar's formation mechanisms—whether driven by tidal forces or internal gravitational instability. Searching for similar objects at even higher redshifts could be the next frontier.
Impact
The results will impact the theory of galaxy formation and evolution, accretion physics and feedback, as well as cosmological models constraining the reionization epoch.
Next steps
High-resolution kinematic data for M1149-BSG-z5 must be obtained using JWST/NIRSpec integral field spectroscopy and ALMA interferometry to measure the velocity field and dispersion.
Key open problems
The discovery touches on several fundamental questions: What are the timescales for disk formation and dynamic cooling? What is the contribution of internal instabilities versus external interactions in the formation of early bars? And how does early baryon domination affect galaxy evolution overall? These issues connect to the broader picture of hierarchical structure growth in ΛCDM cosmology.
🎯 If this bar were visible to the naked eye, its length in the sky would be about 0.7 arcseconds—smaller than the disk of Jupiter!
Key numbers
- redshift: 5.102
- stellar mass: 10^10.45 M⊙
- star formation rate: 144 M⊙/year
- bar length: 4.5 kpc
- effective radius: 2.61 kpc