# Statistical detection of a tidal stream associated with the globular cluster M68 using Gaia data

## TL;DR

This paper introduces a maximum likelihood method to detect and analyze tidal streams in Gaia data, successfully identifying the M68 stream and providing insights into the Milky Way's gravitational potential.

## Contribution

The paper presents a novel statistical method for detecting tidal streams and applies it to Gaia data, identifying the M68 stream and estimating the Milky Way's dark halo shape.

## Key findings

- Detected the M68 tidal stream passing within 5 kpc of the Sun.
- Confirmed the stream's association with the Fjörm stream.
- Provided a list of 115 probable stream members for follow-up studies.

## Abstract

A method to search for tidal streams and to fit their orbits based on maximum likelihood is presented and applied to the Gaia data. Tests of the method are performed showing how a simulated stream produced by tidal stripping of a star cluster is recovered when added to a simulation of the Gaia catalogue. The method can be applied to search for streams associated with known progenitors or to do blind searches in a general catalogue. As the first example, we apply the method to the globular cluster M68 and detect its clear tidal stream stretching over the whole North Galactic hemisphere, and passing within 5 kpc of the Sun. This is one of the closest tidal streams to us detected so far, and is highly promising to provide new constraints on the Milky Way gravitational potential, for which we present preliminary fits finding a slightly oblate dark halo consistent with other observations. We identify the M68 tidal stream with the previously discovered Fj\"orm stream by Ibata et al. The tidal stream is confirmed to contain stars that are consistent with the HR-diagram of M68. We provide a list of 115 stars that are most likely to be stream members, and should be prime targets for follow-up spectroscopic studies.