Detection of Satellite Remnants in the Galactic Halo with Gaia - II. A modified Great Circle Cell Method

TL;DR

This paper extends the Great Circle Cell method to include kinematic constraints, significantly improving the detection of satellite remnants in the Gaia data despite observational errors and phase mixing.

Contribution

It introduces a modified GC3 method that incorporates velocity vector constraints, enhancing the identification of stellar streamers in Gaia data.

Findings

Kinematic restriction greatly improves streamer contrast against background.

Method effectively detects satellites with luminosities of 10^8-10^9 Lsun up to 10 Gyr old.

High-quality astrometric data is crucial for successful detection.

Abstract

We propose an extension of the GC3 streamer finding method of Johnston et al. 1996 that can be applied to the future Gaia database. The original method looks for streamers along great circles in the sky, our extension adds the kinematical restriction that velocity vectors should also be constrained to lie along these great circles, as seen by a Galactocentric observer. We show how to use these combined criteria starting from heliocentric observables. We test it by using the mock Gaia catalogue of Brown et al. 2005, which includes a realistic Galactic background and observational errors, but with the addition of detailed star formation histories for the simulated satellites. We investigate its success rate as a function of initial satellite luminosity, star formation history and orbit. We find that the inclusion of the kinematical restriction vastly enhances the contrast between a streamer and the background, even in the presence of observational errors, provided we use only data with good astrometric quality (fractional errors of 30 per cent or better). The global nature of the method diminishes the erasing effect of phase mixing and permits the recovery of merger events of reasonable dynamical age. Satellites with a star formation history different to that of the Galactic background are also better isolated. We find that satellites in the range of 10^8-10^9 Lsun can be recovered even for events as old as ~10 Gyr. Even satellites with 4-5x10^7 Lsun can be recovered for certain combinations of dynamical ages and orbits.