A comparison of the local spiral structure from Gaia DR2 and VLBI maser parallaxes

TL;DR

This study compares the spiral structure of our galaxy as revealed by Gaia DR2 data and VLBI maser parallaxes, finding good agreement and extending models into new regions with potential new features.

Contribution

It provides a detailed comparison of Gaia DR2 and VLBI maser data for mapping the Milky Way's spiral arms, highlighting new structures and confirming existing models.

Findings

Gaia DR2 spiral structure agrees with VLBI maser results within 1.4 kpc.

O-type stars from Gaia extend spiral arm models into the fourth Galactic quadrant.

Evidence suggests a new spur between the Local and Sagittarius arms.

Abstract

Context. The Gaia mission has released the second data set (Gaia DR2), which contains parallaxes and proper motions for a large number of massive, young stars. Aims. We investigate the spiral structure in the solar neighborhood revealed by Gaia DR2 and compare it with that depicted by VLBI maser parallaxes. Methods. We examined three samples with different constraints on parallax uncertainty and distance errors and stellar spectral types: (1) all OB stars with parallax errors of less than 10%; (2) only O-type stars with 0.1 mas errors imposed and with parallax distance errors of less than 0.2 kpc; and (3) only O-type stars with 0.05 mas errors imposed and with parallax distance errors of less than 0.3 kpc. Results. In spite of the significant distance uncertainties for stars in DR2 beyond 1.4 kpc, the spiral structure in the solar neighborhood demonstrated by Gaia agrees well with that illustrated by VLBI maser results. The O-type stars available from DR2 extend the spiral arm models determined from VLBI maser parallaxes into the fourth Galactic quadrant, and suggest the existence of a new spur between the Local and Sagittarius arms.