A resonant feature near the Perseus arm revealed by red clump stars

TL;DR

This study uses red clump stars to identify a resonant feature near the Perseus arm, revealing extinction peaks, velocity dispersion variations, and a bifurcation in radial velocities linked to galactic resonances.

Contribution

It provides new observational evidence of a resonant feature near the Perseus arm through extinction, velocity dispersion, and velocity distribution analysis of red clump stars.

Findings

Extinction peaks at 9.5 and 12.5 kpc, aligning with spiral arms.

Velocity dispersion peaks around 10 kpc, indicating the Perseus arm.

Radial velocity distribution bifurcates near 10-11 kpc, suggesting resonance effects.

Abstract

We investigate the extinction together with the radial velocity dispersion and distribution of red clump stars in the anti-center direction using spectra obtained with Hectospec on the MMT. We find that extinction peaks at Galactocentric radii of about 9.5 and 12.5 kpc, right in front of the locations of the Perseus and Outer arms and in line with the relative position of dust and stars in external spiral galaxies. The radial velocity dispersion peaks around 10kpc, which coincides with the location of the Perseus arm, yields an estimated arm-interarm density contrast of 1.3-1.5 and is in agreement with previous studies. Finally, we discover that the radial velocity distribution bifurcates around 10-11 kpc into two peaks at +27 km/s and -4 km/s. This seems to be naturally explained by the presence of the outer Lindblad resonance of the Galactic bar, but further observations will be needed to understand if the corotation resonance of the spirals arms also plays a role.