Projection Effects in Barred Galaxies Causing Wrong Interpretation of Radial Flows

TL;DR

This study demonstrates that projection effects in barred galaxy disks can lead to significant misinterpretation of radial flows and rotation curves when using kinematic modeling algorithms assuming circular orbits.

Contribution

It quantifies how projection effects cause spurious radial flow detections and incorrect rotation curves in barred galaxies using simulated data and the 3D-Barolo algorithm.

Findings

Projection effects cause up to 92 km/s spurious radial velocities.

Rotation curves are misestimated by up to 150 km/s within the bar region.

Radial flows can be mistaken for non-circular motions due to projection effects.

Abstract

Galaxy disks in rotation are sometimes the site of radial flows, especially in their gas component. It is important to estimate the outflows, due to AGN or supernovae feedback, or inflows due to bar gravity torques. However, these radial flows may be confused with non-circular motions, which are quite frequent in the center of galaxy disks. We use a simulated giant, barred spiral galaxy from the GalMer database to study the non-circular motions induced by the bar. Our goal is to identify the spurious radial flows that kinematics modeling algorithms can detect, assuming circular orbits for the gas. Using mock data of a strongly barred galaxy, we quantify the radial velocities computed by the 3D-Barolo algorithm for different disk inclinations and several bar orientations in the plane of the sky: along the major and minor kinematic axes and at 45{\deg} from them. Our results show that projection effects cause kinematics modeling algorithms to confuse the radial component of velocity due to elliptical orbits with significant radial flows with mean values up to 92 km.s$^{-1}$, within the bar region. The computed rotation curve is also wrongly estimated inside the bar region, by as much as 150 km.s$^{-1}$ for the highest inclination.