Molecular Distribution in the Spiral Arm of M51

TL;DR

This study maps molecular distributions in M51's spiral arm, revealing that most molecules trace the arm similarly, with slight differences suggesting some are influenced by galactic-scale phenomena rather than local star formation.

Contribution

It provides high-resolution molecular maps of M51's spiral arm and identifies subtle distribution differences linked to galactic-scale processes, advancing understanding of chemical composition in spiral arms.

Findings

Most molecules trace the spiral arm similarly.

CH3OH and HNCO distributions differ slightly from other molecules.

These molecules are influenced by galactic-scale phenomena, not just star formation.

Abstract

Molecular line images of 13CO, C18O, CN, CS, CH3OH, and HNCO are obtained toward the spiral arm of M51 at a 7" times 6" resolution with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). Distributions of the molecules averaged over a 300 pc scale are found to be almost similar to one another and to essentially trace the spiral arm. However, the principal component analysis shows a slight difference of distributions among molecular species particularly for CH3OH and HNCO. These two species do not correlate well with star-formation rate, implying that they are not enhanced by local star-formation activities but by galactic-scale phenomena such as spiral shocks. Furthermore, the distribution of HNCO and CH3OH are found to be slightly different, whose origin deserves further investigation. The present results provide us with an important clue to understanding the 300 pc scale chemical composition in the spiral arm and its relation to galactic-scale dynamics.