Ionizing feedback from an O star formed in a shock-compressed layer. Issue 4 (18th October 2022)

• Record Type: Journal Article
• Authors: Whitworth, A P; Priestley, F D; Geen, S T
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 517:Issue 4(2022)
• Page Start: 4940
• Page End: 4949
• Publication Date: 2022-10-18
• Subjects: hydrodynamics -- stars: formation -- ISM: bubbles -- ISM: clouds -- H ii regions -- ISM kinematics and dynamics; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac2955
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We develop a simple analytical model for what happens when an O star (or compact cluster of OB stars) forms in a shock-compressed layer and carves out an approximately circular hole in the layer, at the waist of a bipolar H ii region (H ii R). The model is characterized by three parameters: the half-thickness of the undisturbed layer, $Z_{_{\rm LAYER}}$, the mean number density of hydrogen molecules in the undisturbed layer, $n_{_{\rm LAYER}}$, and the (collective) ionizing output of the star(s), $\dot{\cal N}_{_{\rm LyC}}$ . The radius of the circular hole is given by $W_{_{\rm IF}}(t)\sim 3.8\, {\rm pc}\, [Z_{_{\rm LAYER}}/0.1\, {\rm pc}]^{-1/6}[n_{_{\rm LAYER}}/10^4\, {\rm cm^{-3}}]^{-1/3}[\dot{\cal N}_{_{\rm LyC}}/10^{49}\, {\rm s^{-1}}]^{1/6}[t/{\rm Myr}]^{2/3}$ . Similar power-law expressions are obtained for the rate at which ionized gas is fed into the bipolar lobes, the rate at which molecular gas is swept up into a dense ring by the shock front that precedes the ionization front, and the density in this dense ring. We suggest that our model might be a useful zeroth-order representation of many observed H ii Rs. From viewing directions close to the mid-plane of the layer, the H ii R will appear bipolar. From viewing directions approximately normal to the layer, it will appear to be a limb-brightened shell but too faint through the centre to be a spherically symmetric bubble. From intermediate viewing angles, more complicated morphologies can be expected.