Exploring a Galactic Twin: NGC 3521 and the Milky Way in Metal-THINGS

NGC 3521, a galaxy strikingly similar to the Milky Way in structure, has been studied in the Metal-THINGS project. This research focuses on its chemical evolution, especially the distribution of oxygen and nitrogen abundances, as indicators of its evolutionary history. Understanding whether NGC 3521 is a structural and evolutionary analogue—or twin—of the Milky Way helps refine theories of galaxy formation and evolution.

Observations and Methodology

Researchers used the Harlan Schmidt telescope and the GCMS spectrograph to collect spectrophotometric data across three regions of NGC 3521. Data was processed to correct instrumental and environmental effects. A key step involved calibrating oxygen abundances to align with methods used for the Milky Way, ensuring consistent comparisons. The observations relied on advanced spectroscopy techniques to assess chemical composition through emission line analysis.

Chemical Gradients and Breaks

The oxygen and nitrogen abundance gradients in NGC 3521 revealed a distinct pattern. In the inner disk, oxygen levels remain constant, while at larger radii, they decline. Nitrogen gradients break closer to the center than oxygen, reflecting the staggered timelines of star formation and element production. These findings align with the inside-out galaxy formation model, suggesting more rapid evolution in the central regions compared to the outskirts.

Comparing NGC 3521 and the Milky Way

NGC 3521's structural parameters—stellar mass, rotation velocity, and central black hole mass—mirror those of the Milky Way. However, their evolutionary paths diverge. For instance, oxygen abundances in the outer Milky Way are lower, possibly due to mass exchange with the surrounding medium, a phenomenon less pronounced in NGC 3521.

Implications and Conclusion

This study underscores the nuanced differences between structural and evolutionary galaxy analogues. While NGC 3521 may be a Milky Way twin in structure, its chemical evolution suggests unique processes at play. These insights refine our understanding of how galaxies like the Milky Way evolve and interact with their environments. Future work will delve deeper into the mechanisms driving these distinctions.

Source: Pilyugin