Ionized gas kinematics in bipolar H ii regions

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Abstract

Stellar feedback plays a fundamental role in shaping the evolution of galaxies. Here we explore the use of ionised gas kinematics in young, bipolar H ii regions as a probe of early feedback in these star-forming environments. We have undertaken a multiwavelength study of a young, bipolar H ii region in the Galactic disc, G316.81-0.06, which lies at the centre of a massive ( 10 3 M ) infrared-dark cloud filament. It is still accreting molecular gas as well as driving a 0.2 pc ionised gas outflow perpendicular to the filament. Intriguingly, we observe a large velocity gradient (47.81 3.21 km s -1 pc -1 ) across the ionised gas in a direction perpendicular to the outflow. This kinematic signature of the ionised gas shows a reasonable correspondence with the simulations of young H ii regions. Based on a qualitative comparison between our observations and these simulations, we put forward a possible explanation for the velocity gradients observed in G316.81-0.06. If the velocity gradient perpendicular to the outflow is caused by rotation of the ionised gas, then we infer that this rotation is a direct result of the initial net angular momentum in the natal molecular cloud. If this explanation is correct, this kinematic signature should be common in other young (bipolar) H ii regions. We suggest that further quantitative analysis of the ionised gas kinematics of young H ii regions, combined with additional simulations, should improve our understanding of feedback at these early stages.

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