Diffuse $\gamma$-ray emission around the massive star forming region of Carina Nebula Complex

TL;DR

This paper reports the detection and analysis of GeV gamma-ray emission around the Carina Nebula Complex, revealing both point source and diffuse emissions linked to cosmic ray interactions with ambient gas.

Contribution

It provides the first detailed spatial and spectral analysis of gamma-ray emission in the Carina Nebula, identifying hadronic processes and cosmic ray interactions as key sources.

Findings

Gamma-ray emission from Eta Carina is identified as a point source.

Diffuse gamma-ray emission correlates with molecular gas regions.

Spectral analysis suggests hadronic cosmic ray interactions.

Abstract

We report the Fermi Large Area Telescope (Fermi-LAT) detection of the $\gamma$-ray emission toward the massive star forming region of Carina Nebula Complex (CNC). Using the latest source catalog and diffuse background models, we found that the GeV $\gamma$-ray emission in this region can be resolved into three different components. The GeV $\gamma$-ray emission from the central point source is considered to originate from the Eta Carina ($\eta$ Car). We further found the diffuse GeV $\gamma$-ray emission around the CNC which can be modelled by two Gaussian disks with radii of 0.4\deg (region A) and 0.75\deg (region B), respectively. The GeV $\gamma$-ray emission from both the regions A and B have good spatial consistency with the derived molecular gas in projection on the sky. The GeV $\gamma$-ray emission of region A reveals a characteristic spectral shape of the pion-decay process, which indicates that the $\gamma$-rays are produced by the interactions of hadronic cosmic rays with ambient gas. The $\gamma$-rays spectrum of region B has a hard photon index of 2.12 $\pm$ 0.02, which is similar to other young massive star clusters. We argue that the diffuse GeV $\gamma$-ray emission in region A and region B likely originate from the interaction of accelerated protons in clusters with the ambient gas.