Young stars raining through the Galactic Halo: the nature and orbit of Price-Whelan 1

TL;DR

This study investigates the properties and orbit of the young stellar system Price-Whelan 1 in the Galactic Halo, revealing its velocity and possible origins, and suggesting it may be associated with a high velocity cloud or disrupted gas.

Contribution

First measurement of radial velocities for PW 1 stars, providing new insights into its orbit and origin in the Galactic Halo.

Findings

PW 1's systemic velocity is 275 km/s, larger than nearby gas.

The gas associated with PW 1 is spatially and kinematically offset from the stars.

PW 1 may be linked to a high velocity cloud or disrupted gas cloud.

Abstract

We present radial velocities for five member stars of the recently discovered young (age= 100-150 Myr) stellar system Price-Whelan 1 (PW 1), that is located far away in the Galactic Halo (D~ 29 kpc, Z~ 15 kpc), and that is probably associated to the Leading Arm (LA) of the Magellanic Stream. We measure the systemic radial velocity of PW 1, V_r=275 +/- 10 km/s, significantly larger than the velocity of the LA gas in the same direction. We re-discuss the main properties and the origin of this system in the light of these new observations, computing the orbit of the system and comparing its velocity with that of the HI in its surroundings. We show that the bulk of the gas at the velocity of the stars is more than 10 deg (5~kpc) away from PW 1 and the velocity difference between the gas and the stars become larger as gas closer to the stars is considered. We discuss the possibilities that (a) the parent gas cloud was dissolved by the interaction with the Galactic gas, and (b) that the parent cloud is the high velocity cloud HVC287.5+22.5+240, lagging behind the stellar system by ~25 km/s and ~10 deg.