JWST Detects Barred Spiral Galaxy M1149-BSG-z5 at z=5.102 in MACS J1149 Parallel Field
Preprint reports a structurally mature barred spiral at z=5.102 with 4.5 kpc bar and 144 solar-mass/yr star formation. The find challenges early disk-assembly timelines and points to interaction-driven or gravitational-instability channels. Evidence rests on imaging decomposition of one system; spectroscopic follow-up is needed.
Wang et al. analyzed NIRCam and HST imaging in the MACS J1149 parallel field using isophote ellipse fitting and two-dimensional structural decomposition. They measured a bar length of 4.5 kpc, spiral arms peaking at 5.5 kpc, global Sérsic index 2.37, and effective radius 2.61 kpc. Emission-line ratios and a broad-line AGN component indicate chemical maturity and a black-hole-to-stellar mass ratio of 10^-3. The galaxy sits in an overdense region with a companion, consistent with interaction-triggered bar formation under gas-rich, baryon-dominated conditions.
Standard Lambda-CDM simulations predict bars should be rare before z2 because disks are dynamically hot and gas fractions are high. This object at z=5.1 therefore requires either earlier disk settling or a bar-formation channel that operates on <1 Gyr timescales. Its size and mass also exceed the typical z5 population, suggesting selection effects in current luminosity-limited samples may hide a larger population of evolved systems.
The study is a single-object discovery based on imaging alone. Spectroscopic confirmation of the redshift, bar kinematics, and dynamical state is still required. Deeper ALMA or JWST IFU data on a statistically meaningful sample of z>4 massive galaxies would test whether bars are common or exceptional at these epochs.
Wang et al.: IFU spectroscopy of 30 additional z>4.5 galaxies above 10^10 solar masses will detect stable bars in at least 15 percent within 18 months.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2606.25022)
- [2]Supporting Source(https://arxiv.org/abs/2305.03069)