Stars with fast Galactic rotation observed in Gaia TGAS: a signature driven by the Perseus arm?

TL;DR

This paper identifies a small group of stars with higher than average galactic rotation speeds in Gaia TGAS data, possibly linked to the Perseus spiral arm's co-rotation resonance, revealing new insights into galactic dynamics.

Contribution

It reports the detection of a distinct overdensity of fast rotators in Gaia TGAS data and suggests a novel connection to the Perseus spiral arm's resonance effects.

Findings

Detection of a 20 km/s higher Galactocentric rotation velocity in a star overdensity.

Fast rotators are more prominent outside the Solar radius.

Velocity of these stars is consistent up to 0.6 kpc from the Sun.

Abstract

We report on the detection of a small overdensity of stars in velocity space with systematically higher Galactocentric rotation velocity than the Sun by about 20 km s$^{-1}$ in the $Gaia$ Data Release 1 Tycho-Gaia astrometric solution (TGAS) data. We find these fast Galactic rotators more clearly outside of the Solar radius, compared to inside of the Solar radius. In addition, the velocity of the fast Galactic rotators is independent of the Galactocentric distance up to $R-R_{\odot}\sim0.6$ kpc. Comparing with numerical models, we qualitatively discuss that a possible cause of this feature is the co-rotation resonance of the Perseus spiral arm, where the stars in peri-centre phase in the trailing side of the Perseus spiral arm experience an extended period of acceleration owing to the torque from the Perseus arm.