News, September 2023
A JWST investigation into the bar fraction at redshifts 1 < z < 3
JWST finds many previously unknown barred galaxies in the early Universe, according to a study by Zoe Le Conte and collaborators
Figure 6 of the paper.
A new study led by Zoe Le Conte from the Centre for Extragalactic Astronomy has found that stellar bars in a disc galaxy are much more common in the early Universe than previously thought. By analysing data from the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST), Le Conte and collaborators determined that the bar fraction in disc galaxies between 8 and 10 billion years ago rises from 6% (as found previously with HST) to 20% (with more powerful JWST data). Stellar bars are elongated structures that form within disc galaxies, and their presence signifies that the galaxy has a stable disc and that bar-driven processes are at work in shaping the galaxy's evolution. Understanding the cosmic evolution of the bar fraction is therefore crucial for gaining insights into galaxy evolution as a whole. Previous studies using the HST had indicated that the bar fraction declines significantly from the local Universe to redshifts near one (8 billion years ago). However, Le Conte's study goes a step further by extending the analysis to higher redshifts, specifically redshifts between 2 and 3 (up to 11.5 billion years ago), finding many more bars than previous studies. To conduct the study, Le Conte used data from the JWST's Cosmic Evolution Early Release Science Survey and the Public Release Imaging for Extragalactic Research. These observations were combined with data from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey, which provided a sample of galaxies suitable for analysis. In total, 768 close-to-face-on galaxies were visually classified to determine the bar fraction in two redshift bins: 1 to 2, and 2 to 3. The results of the study revealed that the bar fraction decreases from approximately 20% in the lower redshift bin to approximately 7% in the higher redshift bin. However, the bar fraction found in this study is still about 3 to 4 times greater than that found in previous studies using bluer filters on the HST. Even with the improved capabilities of JWST, the study still misses shorter, less prominent bars. Therefore, the bar fraction is thought to be even greater. These findings suggest that bar-driven evolution in disc galaxies begins at early cosmic times, and that dynamically settled discs are already present at a lookback time of approximately 11 billion years. Overall, this study provides valuable insights into the evolution of disc galaxies and highlights the importance of bar-driven processes in shaping their morphology and structure. Source: Le Conte et al. (2023), arXiv:2309.10038.