The stretching of Hercules
A. J. Deason (Cambridge), V. Belokurov (Cambridge), N. W. Evans, (Cambridge), L. L. Watkins (MPIA), M. Fellhauer (Chile)
TL;DR
This study uses spectroscopy to identify and analyze blue horizontal branch stars around the Hercules ultrafaint dwarf galaxy, revealing evidence of tidal stripping and an elongated, distended morphology.
Contribution
It provides the first spectroscopic evidence of tidal stripping in Hercules and highlights the importance of velocity gradients in understanding galaxy morphology.
Findings
Eight Hercules BHB members identified
Evidence of stars tidally stripped from Hercules
Velocity gradient supports tidal disruption scenario
Abstract
We present VLT/FORS2 spectroscopy of candidate blue horizontal branch (BHB) stars in the vicinity of the Hercules ultrafaint dwarf galaxy. We identify eight convincing Hercules BHB members, and a further five stars with similar systemic velocities to that of Hercules, but ~ 0.5 kpc from the centre of the galaxy along its major axis. It is likely that these stars once belonged to Hercules, but have been tidally stripped and are now unbound. We emphasise the usefulness of looking for any gradient in the systemic velocity of this stretched system, which would further support our interpretation of the origin of its elongated and distended morphology.
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