A wind-blown bubble in the Central Molecular Zone cloud G0.253+0.016

Abstract

G0.253+0.016, commonly referred to as "the Brick" and located within the Central Molecular Zone, is one of the densest ($\approx 10^{3-4}$ cm${}^{-3}$) molecular clouds in the Galaxy to lack signatures of widespread star formation. We set out to constrain the origins of an arc-shaped molecular line emission feature located within the cloud. We determine that the arc, centred on $\{l_0,b_0\}=\{0.248^{\circ },0.18^{\circ }\}$, has a radius of $1.3$ pc and kinematics indicative of the presence of a shell expanding at $5.2_{-1.9}^{+2.7}$ km s${}^{-1}$. Extended radio continuum emission fills the arc cavity and recombination line emission peaks at a similar velocity to the arc, implying that the molecular and ionised gas are physically related. The inferred Lyman continuum photon rate is $N_{\mathrm{LyC}}=10^{46.0}-10^{47.9}$ photons s${}^{-1}$, consistent with a star of spectral type B1-O8.5, corresponding to a mass of $\approx 12-20$ M${}_{\odot }$. We explore two scenarios for the origin of the arc: i) a partial shell swept up by the wind of an interloper high-mass star; ii) a partial shell swept up by stellar feedback resulting from in-situ star formation. We favour the latter scenario, finding reasonable (factor of a few) agreement between its morphology, dynamics, and energetics and those predicted for an expanding bubble driven by the wind from a high-mass star. The immediate implication is that G0.253+0.016 may not be as quiescent as is commonly accepted. We speculate that the cloud may have produced a $\lesssim 10^3$ M${}_{\odot }$ star cluster $\gtrsim 0.4$ Myr ago, and demonstrate that the high-extinction and stellar crowding observed towards G0.253+0.016 may help to obscure such a star cluster from detection.

17 pages, 7 figures. Accepted for publication in MNRAS (October 15, 2021)