X-rays from a newly discovered superbubble in M31

ABSTRACT A superbubble is a hot, dilute, and X-ray-emitting gas cavity produced by stellar winds and supernova explosions. It is an intriguing feature for the study of stellar feedback processes. We report a study of possible superbubbles in the Andromeda Galaxy (M31). We identify one out of 83 extended sources as a strong superbubble candidate, SB1, from the M31 X-ray source catalogue. SB1 is located in the northern disc of M31 and exhibits soft, extended X-ray emission surrounded by an Hα shell. The XMM–Newton spectral analysis reveals that SB1 has a temperature of ∼0.14 keV and an X-ray luminosity of $L_{\rm X}\sim 3.5\times 10^{37}\,{\rm erg\, s}^{-1}$ in the 0.3–10.0 keV band. Two stellar clusters are found at the west rim of SB1. The estimated age of SB1 is similar to that of an overlapping young stellar cluster, and the colour-magnitude diagram reveals the presence of young stellar objects with an age of less than 10 Myr. We propose that SB1 is a superbubble, likely having triggered star formation in this cluster by compressing the accumulated gas, thereby leading to the formation of gas-dense regions.