# Gaia-DR2 distance to the W3 Complex in the Perseus Arm

## TL;DR

This study uses Gaia-DR2 data to accurately measure the distance to the W3 Complex in the Perseus Arm, resolving previous discrepancies and revealing differential distances within the complex.

## Contribution

It provides the first Gaia-DR2 based distance to the W3 Complex and identifies internal differential distances among its regions, improving understanding of its structure.

## Key findings

- Gaia-DR2 distance to W3 Complex is approximately 2.14 kpc.
- Different parts of W3 show slightly different distances, indicating a complex internal structure.
- The W3 Cluster is the oldest region, likely triggering star formation in surrounding areas.

## Abstract

The Perseus Arm is the closest Galactic spiral arm from the Sun, offering an excellent opportunity to study in detail its stellar population. However, its distance has been controversial with discrepancies by a factor of two. Kinematic distances are in the range 3.9-4.2 kpc as compared to 1.9-2.3 kpc from spectrophotometric and trigonometric parallaxes, reinforcing previous claims that this arm exhibits peculiar velocities. We used the astrometric information of a sample of 31 OB stars from the star-forming W3 Complex to identify another 37 W3 members and to derive its distance from their Gaia-DR2 parallaxes with improved accuracy. The Gaia-DR2 distance to the W3 Complex,2.14$^{+0.08}_{-0.07}$ kpc, coincides with the previous stellar distances of $\sim$ 2 kpc. The Gaia-DR2 parallaxes tentatively show differential distances for different parts of the W3 Complex: W3 Main, located to the NE direction, is at 2.30$^{+0.19}_{-0.16}$ kpc, the W3 Cluster (IC 1795), in the central region of the complex, is at 2.17$^{+0.12}_{-0.11}$ kpc, and W3(OH) is at 2.00$^{+0.29}_{-0.23}$ kpc to the SW direction. The W3 Cluster is the oldest region, indicating that it triggered the formation of the other two star-forming regions located at the edges of an expanding shell around the cluster.