Extended GeV $\gamma$-ray emission around the star forming region of the W3 complex

TL;DR

This study analyzes 14 years of Fermi-LAT data to resolve GeV gamma-ray emissions around the W3 star-forming region, identifying both hadronic and potential cluster-related sources, and suggesting cosmic ray origins from cluster winds and supernova remnants.

Contribution

First detailed gamma-ray analysis of the W3 complex resolving multiple emission components and proposing their origins from cosmic ray interactions and star cluster activity.

Findings

Gamma-ray emissions are resolved into an elliptical Gaussian and a point source.

The elliptical Gaussian's spectrum favors a hadronic origin from cosmic ray interactions.

The point source is likely powered by the W3 Main star cluster.

Abstract

We analyze the GeV $\gamma$-ray emission from the W3 complex using about 14 years of Pass 8 data recorded by the $\it Fermi$ Large Area Telescope (\textit{Fermi}-LAT). We resolve the $\gamma$-ray emissions around W3 into two components: an elliptical Gaussian overlapping with the molecular gas and a point-like source near the cluster W3 Main. The pion-bump feature of SED for the elliptical Gaussian together with the better fitting result of pion decay model favor the hadronic origin. We further argue that the cosmic rays (CRs) could originate from the interactions between cluster winds and the shock produced by the SNR HB3. The point-like source positionally coincident with the star cluster W3 Main indicates it may be directly powered by near clusters, while its fainter $\gamma$-ray emissions below 10 GeV is possibly due to the shelter from dense gas making the low-energy CRs incapable of penetrating the dense materials. Meanwhile, we cannot rule out that the $\gamma$-ray emissions originate from the interaction of accelerated protons in SNR with the ambient gas.