How Do Bars Affect the Evolution of Disc Galaxies?
Galaxies come in many shapes and sizes, and one of the most common features found in disc galaxies is a "bar"—a structure of stars stretching across the center of the galaxy. While bars are thought to influence how galaxies evolve by moving gas and stars around, their exact role remains uncertain. In this study, Pius Privatus and Umananda Dev Goswami examine how the presence of bars affects the way disc galaxies evolve in different environments, using data from the Mapping Nearby Galaxies at APO (MaNGA) survey.
Investigating Galaxies with and without Bars
To conduct this research, the authors used a sample of disc galaxies that had been classified by the Galaxy Zoo 2 project. These galaxies were split into two categories: those with bars and those without. Additionally, galaxies were sorted based on their environment—either as "field galaxies" (isolated galaxies) or "group galaxies" (those found in clusters or groups). The authors then compared several key properties of these galaxies, including their stellar mass, star formation rate (SFR), color (g - r index), concentration index, and gas-phase metallicity (a measure of the abundance of heavy elements in a galaxy).
Key Findings: Bars Reduce Environmental Influence
One of the main findings of the study is that barred galaxies show weaker dependence on their environment compared to unbarred galaxies. While the properties of unbarred galaxies—such as their mass, star formation rate, and color—varied significantly depending on whether they were in a group or isolated, barred galaxies exhibited much less variation. This suggests that the presence of a bar stabilizes a galaxy’s evolution, making it less sensitive to external factors like nearby galaxies or large-scale cosmic structures.
Comparing Galaxy Properties
By analyzing relationships between galaxy properties, the authors found that unbarred galaxies strongly depend on their environment for star formation rate, color, and metallicity, while barred galaxies exhibit weaker environmental influence. Unbarred galaxies in groups generally have higher star formation rates, redder colors, and greater concentration indices than isolated ones, but these differences are less pronounced in barred galaxies. Additionally, unbarred galaxies show significant variation in metallicity based on environment, whereas barred galaxies maintain a more uniform metallicity, suggesting bars help regulate internal chemical evolution regardless of surroundings.
What Do These Results Mean?
The results suggest that bars play an important role in shaping a galaxy's evolution by making it less influenced by its surroundings. This could be due to the way bars help transport gas inward, fueling star formation in the galaxy’s center and regulating other processes that would otherwise be affected by environmental factors. The study highlights the need to consider bars when studying galaxy evolution, as they appear to act as stabilizing structures.
Conclusion
Bars in disc galaxies are more than just visual features—they actively shape how galaxies grow and evolve. This study provides evidence that bars reduce a galaxy’s dependence on its environment, making them an important factor in understanding galaxy formation. By using large surveys like MaNGA, astronomers can continue to explore these fascinating structures and their role in the universe.
Source: Privatus
