Spectroscopic hint of a cold stream in the direction of the globular cluster NGC 1851

TL;DR

This study uses spectroscopic data to identify stars around NGC 1851, revealing a potential stellar stream with a velocity peak that suggests an extragalactic origin, extending our understanding of the cluster's environment.

Contribution

The paper provides the first spectroscopic evidence of a possible stellar stream near NGC 1851, indicating an external origin and challenging existing models of the cluster's outskirts.

Findings

Identification of cluster stars beyond the predicted tidal radius.

Detection of a cold velocity peak at ~180 km/s suggesting a stellar stream.

Evidence supporting an extragalactic origin of the stream.

Abstract

We present the results of a spectroscopic survey performed in the outskirts of the globular cluster NGC1851 with VIMOS@VLT. The radial velocities of 107 stars in a region between 12' and 33' around the cluster have been derived. We clearly identify the cluster stellar population over the entire field of view, indicating the presence of a significant fraction of stars outside the tidal radius predicted by King models. We also find tentative evidence of a cold (sigma_v< 20 km/s) peak in the distribution of velocities at v_r~180 km/s constituted mainly by Main Sequence stars whose location in the color-magnitude diagram is compatible with a stream at a similar distance of this cluster. If confirmed, this evidence would strongly support the extra-Galactic origin of this feature.