PHANGS CO kinematics: disk orientations and rotation curves at 150 pc resolution

TL;DR

This paper introduces a new method for deriving high-resolution rotation curves from CO velocity fields in 67 star-forming galaxies, revealing insights into disk orientations and mass distribution with improved accuracy.

Contribution

A novel fitting technique tailored for CO velocity fields that accurately determines galaxy orientations and rotation curves at 150 pc resolution.

Findings

CO rotation curves reliably trace mass distribution.

Galaxy disks are nearly circular with uniform thickness.

Method reduces impact of non-axisymmetric features.

Abstract

We present kinematic orientations and high resolution (150 pc) rotation curves for 67 main sequence star-forming galaxies surveyed in CO (2-1) emission by PHANGS-ALMA. Our measurements are based on the application of a new fitting method tailored to CO velocity fields. Our approach identifies an optimal global orientation as a way to reduce the impact of non-axisymmetric (bar and spiral) features and the uneven spatial sampling characteristic of CO emission in the inner regions of nearby galaxies. The method performs especially well when applied to the large number of independent lines-of-sight contained in the PHANGS CO velocity fields mapped at 1'' resolution. The high resolution rotation curves fitted to these data are sensitive probes of mass distribution in the inner regions of these galaxies. We use the inner slope as well as the amplitude of our fitted rotation curves to demonstrate that CO is a reliable global dynamical mass tracer. From the consistency between photometric orientations from the literature and kinematic orientations determined with our method, we infer that the shapes of stellar disks in the mass range of log($\rm M_{\star}(M_{\odot})$)=9.0-10.9 probed by our sample are very close to circular and have uniform thickness.