Using the MIRI medium-resolution spectrometer on JWST, we have detected pure rotational, suprathermal OH emissions from the vicinity of the intermediate-mass protostar HOPS 370 (OMC2/FIR3). These emissions are observed from shocked knots in a jet/outflow and originate in states of rotational quantum number as high as 46 that possess excitation energies as large as E _U /k = 4.65 × 10⁴ K. The relative strengths of the observed OH lines provide a powerful diagnostic of the ultraviolet radiation field in a heavily extinguished region (A _V ∼ 10–20) where direct UV observations are impossible. To high precision, the OH line strengths are consistent with a picture in which the suprathermal OH states are populated following the photodissociation of water in its B˜−X band by ultraviolet radiation produced by fast (∼80 km s⁻¹) shocks along the jet. The observed dominance of emission from symmetric ( A′ ) OH states over that from antisymmetric (A″) states provides a distinctive signature of this particular population mechanism. Moreover, the variation of intensity with rotational quantum number suggests specifically that Lyα radiation is responsible for the photodissociation of water, an alternative model with photodissociation by a 10⁴ K blackbody being disfavored at a high level of significance. Using measurements of the Brα flux to estimate the Lyα production rate, we find that ∼4% of the Lyα photons are absorbed by water. Combined with direct measurements of water emissions in the ν ₂ = 1 − 0 band, the OH observations promise to provide key constraints on future models for the diffusion of Lyα photons in the vicinity of a shock front.

中文翻译：

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JWST/MIRI 超热 OH 旋转发射的检测：探测原星 HOPS 370 附近 Lyα 光子对水的解离

使用 JWST 上的 MIRI 中分辨率光谱仪，我们检测到中等质量原恒星 HOPS 370 (OMC2/FIR3) 附近的纯旋转超热 OH 发射。这些发射是从喷射/流出中的激波结中观察到的，源自旋转量子数高达 46 的状态，其激发能量高达乙 _U /k= 4.65 × 10 ⁴ K。观测到的 OH 线的相对强度为严重熄灭区域的紫外线辐射场提供了有力的诊断（A _V ∼ 10–20) 无法直接进行紫外线观察。为了高精度，OH 线强度与水光解离后形成超热 OH 态的图片一致。 乙～-X 沿射流的快速（∼80 km s ^-1 ）冲击产生的紫外线辐射带。观察到的对称发射的优势（ A′ ) OH 状态超过反对称 (A”）国家为这种特定的人口机制提供了独特的标志。此外，强度随旋转量子数的变化特别表明 Lyα辐射负责水的光解离，这是一种由 10 ⁴ K 黑体进行光解离的替代模型，在高度显着性方面不受欢迎。使用 Br 的测量值α估计 Ly 的通量α生产率，我们发现~4%的Lyα光子被水吸收。结合水排放的直接测量ν ₂ = 1 − 0 带，OH 观测有望为 Ly 扩散的未来模型提供关键约束α激波前沿附近的光子。