Spiral arms and bars in early galaxies are not just beautiful cosmic features but powerful drivers of star formation. This revelation comes from recent research that challenges our understanding of how galaxies evolved in the early universe. The study, published in two papers, reveals that massive disk galaxies with spiral arms and bars were highly efficient at moving cold gas around, which fueled their high star formation rates (SFRs) during the Cosmic Noon, around two to three billion years after the Big Bang.
The first paper, "Galaxy morphologies at cosmic noon with JWST: A foundation for exploring gas transport with bars and spiral arms," published in Astronomy and Astrophysics, highlights a fundamental question in galaxy evolution: how did early star-forming galaxies develop the well-ordered structures we see today? While previous observations suggested that these early galaxies were chaotic and irregular, more powerful observations with the James Webb Space Telescope (JWST) and the NOrthern Extended Millimeter Array (NOEMA) have shown otherwise.
The second paper, "NOEMA3D: Resolving radial gas flows in disk galaxies at z~1.1-1.6 with high-resolution CO observations," available at arxiv.org, focuses on the kinematics of cold gas in these galaxies. By measuring gas velocities and subtracting the velocities due to rotation, the researchers found that spiral arms and bars are directly linked to the motions of cold gas within galaxies. This provides compelling evidence that these structures were already driving gas transport when the universe was at its peak star-forming activity.
The study, based on NOEMA3D, a survey of cold gas movement in star-forming galaxies during the Cosmic Noon, examined massive main-sequence galaxies with the JWST and NOEMA. The results showed that these galaxies, which were once thought to be rare, are actually well-ordered spirals with clear spiral arms and central bars. This contradicts the previous understanding that early galaxies were clumpy and messy.
The researchers found that the rate of gas inflow into the inner regions of these galaxies is comparable to their SFR, meaning the gas is feeding star formation and may also be contributing to supermassive black holes. This new understanding of how gas is redistributed by spiral arms and bars provides a different picture of the first galaxies, their morphologies, and their high SFRs.
The findings suggest that these ancient galaxies, similar to our modern Milky Way, had well-established spiral arms and bars, which efficiently channeled cold, star-forming gas from their outer regions into their centers. This challenges the previous belief that early galaxies were chaotic and irregular, and it opens up new avenues for understanding galaxy evolution.
In conclusion, the research highlights the importance of spiral arms and bars in the star formation process of early galaxies. It provides a new perspective on the efficiency of gas transport in these galaxies and offers a more nuanced understanding of the universe's early stages.
