JWST discovers most distant barred spiral galaxy

An international team of astronomers announced the discovery of a massive new barred spiral galaxy, designated M1149-BSG-z5, found using the James Webb Space Telescope (JWST).

The discovery was published on June 23 on the arXiv preprint server. Stellar bars are essential in galaxies and closely linked to their long-term evolution. Although they are common in nearby disk galaxies, astronomers generally believe that the chaotic early cosmic environment suppresses bar formation at high redshifts.

The JWST has been instrumental in identifying high-redshift barred galaxies, revealing that these structures can form as early as a redshift of ~4. At a redshift of 3.5, barred galaxies account for an observed fraction of three to seven percent.

A team of astronomers led by Xiaohan Wang from Tsinghua University in Beijing recently added another galaxy to this list. They identified M1149-BSG-z5 in the NIRISS imaging parallel field of JWST Cycle-2’s ‘Medium-band Astrophysics with the Grism of NIRCam in Frontier Fields.’ Sitting at a redshift of 5.1, the galaxy features a stellar bar roughly 14,700 light-years long, making it the most distant barred galaxy known to date.

The study indicates that M1149-BSG-z5 has an effective radius of approximately 8,500 light-years, with spiral arms reaching about 17,900 light-years. Its mass is estimated at 28 billion solar masses, and it forms stars at a rate of 144 solar masses annually.

The discovered galaxy also hosts an active galactic nucleus (AGN) with a black-hole-to-stellar-mass ratio of around 0.001, which is notably lower than that of many high-redshift AGNs and aligns more closely with local galaxies.

READ MORE: Exoplanet GJ 3378b emerges as a better candidate to host life than

previously expected

Astronomers found that M1149-BSG-z5 has a high metallicity, almost 50% of solar levels, and a specific placement on the BPT (Baldwin, Phillips, and Terlevich) diagram. This diagram distinguishes whether a galaxy’s gas is ionized by intense star formation or an active supermassive black hole. These characteristics confirm that it is a large, chemically evolved galaxy despite its high redshift.

Compared to other galaxies, M1149-BSG-z5 is larger than most found around a redshift of 5.0 and is similar in size to barred galaxies with redshifts between 2.0 and 4.0. The authors noted that a companion galaxy sits approximately 69,000 light-years away, suggesting that gravitational interactions might influence the bar formation observed in this newly discovered system.