تقرير
Starburst Energy Feedback Seen Through HCO$^+$/HOC$^+$ Emission in NGC 253 from ALCHEMI
| العنوان: | Starburst Energy Feedback Seen Through HCO$^+$/HOC$^+$ Emission in NGC 253 from ALCHEMI |
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| المؤلفون: | Harada, Nanase, Martín, Sergio, Mangum, Jeffrey G., Sakamoto, Kazushi, Muller, Sebastien, Tanaka, Kunihiko, Nakanishi, Kouichiro, Herrero-Illana, Rubén, Yoshimura, Yuki, Mühle, Stefanie, Aladro, Rebeca, Colzi, Laura, Rivilla, Víctor M., Aalto, Susanne, Behrens, Erica, Henkel, Christian, Holdship, Jonathan, Humire, P. K., Meier, David S., Nishimura, Yuri, van der Werf, Paul P., Viti, Serena |
| سنة النشر: | 2021 |
| المجموعة: | Astrophysics |
| مصطلحات موضوعية: | Astrophysics - Astrophysics of Galaxies |
| الوصف: | Molecular abundances are sensitive to UV-photon flux and cosmic-ray ionization rate. In starburst environments, the effects of high-energy photons and particles are expected to be stronger. We examine these astrochemical signatures through multiple transitions of HCO$^+$ and its metastable isomer HOC$^+$ in the center of the starburst galaxy NGC 253 using data from the ALMA large program ALCHEMI. The distribution of the HOC$^+$(1-0) integrated intensity shows its association with "superbubbles", cavities created either by supernovae or expanding HII regions. The observed HCO$^+$/HOC$^+$ abundance ratios are $\sim 10-150$, and the fractional abundance of HOC$^+$ relative to H$_2$ is $\sim 1.5\times 10^{-11} - 6\times 10^{-10}$, which implies that the HOC$^+$ abundance in the center of NGC 253 is significantly higher than in quiescent spiral-arm dark clouds in the Galaxy and the Galactic center clouds. Comparison with chemical models implies either an interstellar radiation field of $G_0\gtrsim 10^3$ if the maximum visual extinction is $\gtrsim 5$, or a cosmic-ray ionization rate of $\zeta \gtrsim 10^{-14}$ s$^{-1}$ (3-4 orders of magnitude higher than that within clouds in the Galactic spiral-arms) to reproduce the observed results. From the difference in formation routes of HOC$^+$, we propose that a low-excitation line of HOC$^+$ traces cosmic-ray dominated regions, while high-excitation lines trace photodissociation regions. Our results suggest that the interstellar medium in the center of NGC 253 is significantly affected by energy input from UV-photons and cosmic rays, sources of energy feedback. Comment: 57 pages, 32 figures, accepted for publication in ApJ |
| نوع الوثيقة: | Working Paper |
| DOI: | 10.3847/1538-4357/ac26b8 |
| URL الوصول: | http://arxiv.org/abs/2109.06476 |
| رقم الأكسشن: | edsarx.2109.06476 |
| قاعدة البيانات: | arXiv |
| DOI: | 10.3847/1538-4357/ac26b8 |
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