Principal Component Analysis reveals some features in the starburst ring of NGC 1068

ABSTRACT :
Molecular clouds are the sites of star formation, and understanding their properties is essential for exploring galaxy evolution. Since the chemical composition of molecular gas is known to reflect physical properties such as temperature and density, as well as dynamics such as shock waves, investigating the chemical composition of galaxies plays a very important role. NGC 1068 is a nearby Seyfert 2 galaxy known to have an Active Galactic Nucleus (AGN) and a ring-shaped starburst region (Starburst Ring; SB-ring). In this galaxy, many molecular emission lines have been observed. Investigating each molecular emission line in detail to study the phenomena occurring within the galaxy is time-consuming and may require subjective interpretation. Therefore, we used Principal Component Analysis (PCA) to objectively visualize the features of the molecular emission line distributions and extract characteristics of this galaxy. We report the results of the application of PCA to the SB-ring, a region with active star formation and frequent molecular cloud collisions.
The PCA can categorize some features, such as PC2: the region of cloud-cloud-collisions and the region of active star formation, PC3: the region of young starburst activities and the possible region of interactions between AGN outflows and gas. We examined the correlation between PC3 and equivalent width, finding a weak correlation. Additionally, a KS test on the equivalent widths of the PC3_negative region and the PC3_positive region yielded a p-value of approximately 1.0 × 10^-6, indicating a significant difference between the two populations. Based on these results, the PC3 map may represent the impact of interactions between the AGN outflows and gas. This study is the first report that AGN outflows interact with gas in the SB-ring of NGC 1068.