New clues on the extended HeII ionization in IZw18 from GTC/MEGARA and JWST/MIRI
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arXiv
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| Natura: | Preprint |
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2025
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| author | Arroyo-Polonio, A. Kehrig, C. Vílchez, J. M. Iglesias-Páramo, J. Perez-Montero, E. Puertas, S. Duarte Gallego, J. Reverte, D. |
| author_facet | Arroyo-Polonio, A. Kehrig, C. Vílchez, J. M. Iglesias-Páramo, J. Perez-Montero, E. Puertas, S. Duarte Gallego, J. Reverte, D. |
| contents | IZw18 is one of the lowest-metallicity star-forming galaxies known at z$\sim$0, considered a unique local analogue of the first galaxies. The origin of its hard ionizing continuum, expected to be a common feature in the early Universe and traced by He\textsc{ii} emission lines, remains intensely debated and challenging to explain. Here we combine optical (GTC/MEGARA) and mid-infrared (JWST/MIRI) integral field spectroscopic observations for IZw18 to shed new light on the high-ionization phenomenon. This letter reports the first detection of the high-ionization [Ne\textsc{v}]14.32 $μ$m line in IZw18. Its emission is spatially extended and coincident with the He\textsc{ii} peak, revealing the presence of highly energetic ionizing sources that surpass mechanisms previously proposed on the basis of He\textsc{ii} alone. Our kinematic studies highlight that the He\textsc{ii}$λ$4686-emitting gas displays higher velocity dispersions and a different velocity pattern compared to the H$β$ emission, suggesting the presence of energetic processes such as shocks or stellar-driven feedback. Additionally, integrated spectra show asymmetric blueshifted profiles in the He\textsc{ii}$λ$4686 line, possibly indicating \textbf{early-stage} stellar-driven outflows potentially facilitating future ionizing photon leakage. Our spatial analysis also reveals differences in structure between the emission of H$β$ and He\textsc{ii}$λ$4686, with the He\textsc{ii}$λ$4686 peak offset by a projected distance of 140 pc from the peak H$β$ emission. This indicates distinct locations for the most extreme ionizing sources compared to moderate ionizing sources. Our findings underscore the complex interplay of physical processes in extremely metal-poor environments with \textbf{high-ionized} gas, offering new insights into the conditions prevailing in the early galaxies. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_01742 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | New clues on the extended HeII ionization in IZw18 from GTC/MEGARA and JWST/MIRI Arroyo-Polonio, A. Kehrig, C. Vílchez, J. M. Iglesias-Páramo, J. Perez-Montero, E. Puertas, S. Duarte Gallego, J. Reverte, D. Astrophysics of Galaxies IZw18 is one of the lowest-metallicity star-forming galaxies known at z$\sim$0, considered a unique local analogue of the first galaxies. The origin of its hard ionizing continuum, expected to be a common feature in the early Universe and traced by He\textsc{ii} emission lines, remains intensely debated and challenging to explain. Here we combine optical (GTC/MEGARA) and mid-infrared (JWST/MIRI) integral field spectroscopic observations for IZw18 to shed new light on the high-ionization phenomenon. This letter reports the first detection of the high-ionization [Ne\textsc{v}]14.32 $μ$m line in IZw18. Its emission is spatially extended and coincident with the He\textsc{ii} peak, revealing the presence of highly energetic ionizing sources that surpass mechanisms previously proposed on the basis of He\textsc{ii} alone. Our kinematic studies highlight that the He\textsc{ii}$λ$4686-emitting gas displays higher velocity dispersions and a different velocity pattern compared to the H$β$ emission, suggesting the presence of energetic processes such as shocks or stellar-driven feedback. Additionally, integrated spectra show asymmetric blueshifted profiles in the He\textsc{ii}$λ$4686 line, possibly indicating \textbf{early-stage} stellar-driven outflows potentially facilitating future ionizing photon leakage. Our spatial analysis also reveals differences in structure between the emission of H$β$ and He\textsc{ii}$λ$4686, with the He\textsc{ii}$λ$4686 peak offset by a projected distance of 140 pc from the peak H$β$ emission. This indicates distinct locations for the most extreme ionizing sources compared to moderate ionizing sources. Our findings underscore the complex interplay of physical processes in extremely metal-poor environments with \textbf{high-ionized} gas, offering new insights into the conditions prevailing in the early galaxies. |
| title | New clues on the extended HeII ionization in IZw18 from GTC/MEGARA and JWST/MIRI |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2507.01742 |