The tidal stream generated by the globular cluster NGC 3201

TL;DR

This paper reports the detection and modeling of a 140-degree tidal stream from globular cluster NGC 3201 using Gaia DR2 data, identifying likely member stars and confirming the stream's association with the Gjöll stream.

Contribution

The study presents the first detailed detection and modeling of NGC 3201's tidal stream, including a list of high-likelihood member stars for future spectroscopic follow-up.

Findings

Detected a 140-degree tidal stream from NGC 3201.

Identified ~200 likely stream member stars using Gaia kinematics.

Confirmed the stream's association with the Gjöll stream.

Abstract

We detect a tidal stream generated by the globular cluster NGC 3201 extending over ~140 degrees on the sky, using the Gaia DR2 data, with the maximum likelihood method we presented previously to study the M68 tidal stream. Most of the detected stream is the trailing one, which stretches in the southern Galactic hemisphere and passes within a close distance of 3.2 kpc from the Sun, therefore making the stream highly favorable for discovering relatively bright member stars, while the leading arm is further from us and behind a disk foreground that is harder to separate from. The cluster has just crossed the Galactic disk and is now in the northern Galactic hemisphere, moderately obscured by dust, and the part of the trailing tail closest to the cluster is highly obscured behind the plane. We obtain a best-fit model of the stream which is consistent with the measured proper motion, radial velocity and distance to NGC 3201, and show it to be the same as the previously detected Gj\"oll stream by Ibata et al. We identify ~200 stars with the highest likelihood of being stream members using only their Gaia kinematic data. Most of these stars (170) are photometrically consistent with being members of NGC 3201 when they are compared to the cluster H-R diagram, only once a correction for dust absorption and reddening by the Galaxy is applied. The remaining stars are consistent with being random foreground objects according to simulated data sets. We list these 170 highly likely stream member stars, which will be of strong interest to model the gravitational potential of the Milky Way and to be followed up spectroscopically for accurate radial velocities.