Kinematics of massive stars in the Small Magellanic Cloud

TL;DR

This study provides detailed radial velocity measurements for over 2000 stars in the Small Magellanic Cloud, revealing a velocity gradient in the bar and distinct kinematic features in the wing, shedding light on the galaxy's dynamic structure.

Contribution

It offers the first large-scale radial velocity survey of young stars in the SMC, identifying a velocity gradient and differences between the bar and wing regions.

Findings

Velocity gradient of 26.3 km/s/deg in the SMC bar

Distinct velocity distribution in the SMC wing

Mean velocity of +172 km/s for the sample

Abstract

We present radial velocities for 2045 stars in the Small Magellanic Cloud (SMC), obtained from the 2dF survey by Evans et al. (2004). The great majority of these stars are of OBA type, tracing the dynamics of the young stellar population. Dividing the sample into ad hoc `bar' and `wing' samples (north and south, respectively, of the line: $\delta$ = -77$^{\circ}$50' + [4$\alpha$]', where $\alpha$ is in minutes of time) we find that the velocities in the SMC bar show a gradient of 26.3 +/- 1.6 km/s/deg. at a position angle of 126 +/- 4 deg. The derived gradient in the bar is robust to the adopted line of demarcation between the two samples. The largest redshifts are found in the SMC wing, in which the velocity distribution appears distinct from that in the bar, most likely a consequence of the interaction between the Magellanic Clouds that is predicted to have occurred 0.2 Gyr ago. The mean velocity for all stars in the sample is +172.0 +/- 0.2 km/s (redshifted by ~20 km/s when compared to published results for older populations), with a velocity dispersion of 30 km/s.