[C II]-deficit caused by self-absorption in an ionized carbon-filled bubble in RCW79
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| Main Authors: | , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866908339684769792 |
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| author | Keilmann, Eduard Dannhauer, Simon Kabanovic, Slawa Schneider, Nicola Ossenkopf-Okada, Volker Simon, Robert Bonne, Lars Goldsmith, Paul F. Güsten, Rolf Zavagno, Annie Stutzki, Jürgen Riechers, Dominik Röllig, Markus Verbena, Juan L. Tielens, Alexander G. G. M. |
| author_facet | Keilmann, Eduard Dannhauer, Simon Kabanovic, Slawa Schneider, Nicola Ossenkopf-Okada, Volker Simon, Robert Bonne, Lars Goldsmith, Paul F. Güsten, Rolf Zavagno, Annie Stutzki, Jürgen Riechers, Dominik Röllig, Markus Verbena, Juan L. Tielens, Alexander G. G. M. |
| contents | Recent spectroscopic observations of the [C II] 158$\,\mathrm{μm}$ fine-structure line of ionized carbon (C$^+$), using the Stratospheric Observatory for Infrared Astronomy (SOFIA), have revealed expanding [C II] shells in Galactic H II regions. We report the discovery of a bubble-shaped source (S144 in RCW79), associated with a compact H II region, excited by a single O7.5--9.5V/III star, which is consistent with a scenario that the bubble is still mostly ``filled'' with C$^+$. This indicates most likely a very early evolutionary state, in which the stellar wind has not yet blown material away, as it is the case for more evolved H II regions. Using the SimLine non-LTE radiative transfer code, the [C II] emission can be modeled to originate from three regions. First, a central H II region with little C$^+$ in the fully ionized phase, followed by two layers with gas density around $2500\,\mathrm{cm^{-3}}$ of partially photo-dissociated gas. The second layer is a slowly expanding [C II] shell with an expansion velocity of $\sim\,$$2.6\,\mathrm{km\,s^{-1}}$. The outermost layer exhibits a temperature and velocity gradient that produces the observed self-absorption features in the optically thick [C II] line ($τ\sim 4$) leading to an apparent deficit in [C II] emission and a low ratio of [C II] to total far-infrared (FIR) emission. We developed a procedure to approximate the missing [C II] flux and find a linear correlation between [C II] and FIR without a [C II]-deficit. This demonstrates that at least some of the [C II]-deficit found in Galactic H II bubbles can be attributed to self-absorption. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_08976 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | [C II]-deficit caused by self-absorption in an ionized carbon-filled bubble in RCW79 Keilmann, Eduard Dannhauer, Simon Kabanovic, Slawa Schneider, Nicola Ossenkopf-Okada, Volker Simon, Robert Bonne, Lars Goldsmith, Paul F. Güsten, Rolf Zavagno, Annie Stutzki, Jürgen Riechers, Dominik Röllig, Markus Verbena, Juan L. Tielens, Alexander G. G. M. Astrophysics of Galaxies High Energy Astrophysical Phenomena Instrumentation and Methods for Astrophysics High Energy Physics - Phenomenology Recent spectroscopic observations of the [C II] 158$\,\mathrm{μm}$ fine-structure line of ionized carbon (C$^+$), using the Stratospheric Observatory for Infrared Astronomy (SOFIA), have revealed expanding [C II] shells in Galactic H II regions. We report the discovery of a bubble-shaped source (S144 in RCW79), associated with a compact H II region, excited by a single O7.5--9.5V/III star, which is consistent with a scenario that the bubble is still mostly ``filled'' with C$^+$. This indicates most likely a very early evolutionary state, in which the stellar wind has not yet blown material away, as it is the case for more evolved H II regions. Using the SimLine non-LTE radiative transfer code, the [C II] emission can be modeled to originate from three regions. First, a central H II region with little C$^+$ in the fully ionized phase, followed by two layers with gas density around $2500\,\mathrm{cm^{-3}}$ of partially photo-dissociated gas. The second layer is a slowly expanding [C II] shell with an expansion velocity of $\sim\,$$2.6\,\mathrm{km\,s^{-1}}$. The outermost layer exhibits a temperature and velocity gradient that produces the observed self-absorption features in the optically thick [C II] line ($τ\sim 4$) leading to an apparent deficit in [C II] emission and a low ratio of [C II] to total far-infrared (FIR) emission. We developed a procedure to approximate the missing [C II] flux and find a linear correlation between [C II] and FIR without a [C II]-deficit. This demonstrates that at least some of the [C II]-deficit found in Galactic H II bubbles can be attributed to self-absorption. |
| title | [C II]-deficit caused by self-absorption in an ionized carbon-filled bubble in RCW79 |
| topic | Astrophysics of Galaxies High Energy Astrophysical Phenomena Instrumentation and Methods for Astrophysics High Energy Physics - Phenomenology |
| url | https://arxiv.org/abs/2504.08976 |