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| Auteurs principaux: | , , , , , , , , , |
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| Format: | Preprint |
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2025
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| Accès en ligne: | https://arxiv.org/abs/2506.17390 |
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| _version_ | 1866909752091475968 |
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| author | Speranza, G. Pereira-Santaella, M. Agúndez, M. González-Alfonso, E. García-Bernete, I. Goicoechea, J. R. Imanishi, M. Rigopoulou, D. Santa-Maria, M. G. Thatte, N. |
| author_facet | Speranza, G. Pereira-Santaella, M. Agúndez, M. González-Alfonso, E. García-Bernete, I. Goicoechea, J. R. Imanishi, M. Rigopoulou, D. Santa-Maria, M. G. Thatte, N. |
| contents | We analyse the ro-vibrational absorption bands of various molecular cations (HCO$^+$, HCNH$^+$, and N$_2$H$^+$) and neutral species (HCN, HNC, and HC$_3$N) detected in the \textit{James Webb Space Telescope}/Mid-Infrared Instrument Medium Resolution Spectrometer spectrum (4.9--27.9\,$\upmu$m) of the local ultra luminous infrared galaxy IRAS~07251$-$0248. We find that the molecular absorptions are blueshifted by 160\,km\,s$^{-1}$ relative to the systemic velocity of the target. Using local thermal equilibrium (LTE) excitation models, we derive rotational temperatures ($T_{\rm rot}$) from 42 to 185\,K for these absorption bands. This range of measured $T_{\rm rot}$ can be explained by infrared (IR) radiative pumping as a by--product of the strength, effective critical density, and opacity of each molecular band. Thus, these results suggest that these absorptions originate in a warm expanding gas shell ($\dot{M}$$\sim$90--330\,$M_\odot$\,yr$^{-1}$), which might be the base of the larger scale cold molecular outflow detected in this source. Finally, the elevated abundance of molecular cations can be explained by a high cosmic ray ionization rate, with log($ζ_{\text{H}_2}$/n$_{\rm H}\, [\text{cm}^3\, \text{s}^{-1}])$ in the range of $-$18.2 (from H$_3^+$) to $-$19.1 (inferred from HCO$^+$ and N$_2$H$^+$, which are likely tracing denser gas), consistent with a cosmic ray dominated chemistry as predicted by chemical models. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2506_17390 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | JWST reveals cosmic ray dominated chemistry in the local ULIRG IRAS 07251$-$0248 Speranza, G. Pereira-Santaella, M. Agúndez, M. González-Alfonso, E. García-Bernete, I. Goicoechea, J. R. Imanishi, M. Rigopoulou, D. Santa-Maria, M. G. Thatte, N. Astrophysics of Galaxies We analyse the ro-vibrational absorption bands of various molecular cations (HCO$^+$, HCNH$^+$, and N$_2$H$^+$) and neutral species (HCN, HNC, and HC$_3$N) detected in the \textit{James Webb Space Telescope}/Mid-Infrared Instrument Medium Resolution Spectrometer spectrum (4.9--27.9\,$\upmu$m) of the local ultra luminous infrared galaxy IRAS~07251$-$0248. We find that the molecular absorptions are blueshifted by 160\,km\,s$^{-1}$ relative to the systemic velocity of the target. Using local thermal equilibrium (LTE) excitation models, we derive rotational temperatures ($T_{\rm rot}$) from 42 to 185\,K for these absorption bands. This range of measured $T_{\rm rot}$ can be explained by infrared (IR) radiative pumping as a by--product of the strength, effective critical density, and opacity of each molecular band. Thus, these results suggest that these absorptions originate in a warm expanding gas shell ($\dot{M}$$\sim$90--330\,$M_\odot$\,yr$^{-1}$), which might be the base of the larger scale cold molecular outflow detected in this source. Finally, the elevated abundance of molecular cations can be explained by a high cosmic ray ionization rate, with log($ζ_{\text{H}_2}$/n$_{\rm H}\, [\text{cm}^3\, \text{s}^{-1}])$ in the range of $-$18.2 (from H$_3^+$) to $-$19.1 (inferred from HCO$^+$ and N$_2$H$^+$, which are likely tracing denser gas), consistent with a cosmic ray dominated chemistry as predicted by chemical models. |
| title | JWST reveals cosmic ray dominated chemistry in the local ULIRG IRAS 07251$-$0248 |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2506.17390 |