Diverse stages of star formation in the IRAS 18162-2048 region. Emergence of UV Feedback
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| Auteurs principaux: | , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| author | Fedriani, R. Anglada, G. Garatti, A. Caratti o Gómez, J. F. Masqué, J. Osorio, M. Stecklum, B. Rodríguez-Kamenetzky, A. R. Galván-Madrid, R. Carrasco-González, C. Blázquez-Calero, G. Placinta-Mitrea, A. F. Sanna, A. Cesaroni, R. Moscadelli, L. Ray, T. P. Coffey, D. Fuller, G. A. |
| author_facet | Fedriani, R. Anglada, G. Garatti, A. Caratti o Gómez, J. F. Masqué, J. Osorio, M. Stecklum, B. Rodríguez-Kamenetzky, A. R. Galván-Madrid, R. Carrasco-González, C. Blázquez-Calero, G. Placinta-Mitrea, A. F. Sanna, A. Cesaroni, R. Moscadelli, L. Ray, T. P. Coffey, D. Fuller, G. A. |
| contents | Methods: We obtained adaptive optics-assisted integral field spectroscopy in the near-infrared (IR) $K$ band ($1.93-2.47 \mathrm{μm}$) with VLT/SINFONI, complemented by VLA X and C bands (3$-$6 cm) and ALMA band 3 ($\sim$3.3 mm) observations. Results: The near-IR continuum reveals two infrared sources, IRS 2 and IRS 7, while the main protostellar core IRAS 18162-2048 remains undetected up to $2.47 \mathrm{μm}$. IRS 7 shows a peculiar Hydrogen Recombination Line Br$γ$ profile with a narrow emission component superimposed on a broad absorption feature, consistent with a B2/B3 zero-age main-sequence star. Extended H$_2$ emission exhibits a `sawtooth' pattern in the excitation diagram, characteristic of UV radiation in a PDR rather than shock excitation. The radiative transfer model Cloudy reproduces the H$_2$ ro-vibrational populations for $T_\mathrm{gas}=600$ K and $n_\mathrm{H}=7.9\times10^3 \mathrm{cm^{-3}}$. VLA X and C bands observations reveal a compact radio source previously reported as a stationary condensation (SC) and coincident with IRS 7. For the first time, we detect IRS 7/SC in mm wavelengths. The spectral index in the 3$-$6 cm and 3.3 mm regime is consistent with optically thin free-free emission. Conclusions: Our near-IR and radio observations reveal that IRS 7/SC is a B2/B3 ZAMS star that has begun to photoionise its environment, giving rise to an extended PDR and a compact \ion{H}{ii} region. The coexistence of this source with the deeply embedded protostar IRAS 18162-2048 and other bubble-like structures in the field, suggests a multigenerational star-forming environment. Future \textit{James Webb Space Telescope} observations targeting the H$_2$ pure rotational lines ($3-28 \mathrm{μm}$) and other HRLs less affected by extinction will be essential to characterise the cooler molecular and ionised gas to fully disclose the formation history of the region. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2512_07604 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Diverse stages of star formation in the IRAS 18162-2048 region. Emergence of UV Feedback Fedriani, R. Anglada, G. Garatti, A. Caratti o Gómez, J. F. Masqué, J. Osorio, M. Stecklum, B. Rodríguez-Kamenetzky, A. R. Galván-Madrid, R. Carrasco-González, C. Blázquez-Calero, G. Placinta-Mitrea, A. F. Sanna, A. Cesaroni, R. Moscadelli, L. Ray, T. P. Coffey, D. Fuller, G. A. Astrophysics of Galaxies Methods: We obtained adaptive optics-assisted integral field spectroscopy in the near-infrared (IR) $K$ band ($1.93-2.47 \mathrm{μm}$) with VLT/SINFONI, complemented by VLA X and C bands (3$-$6 cm) and ALMA band 3 ($\sim$3.3 mm) observations. Results: The near-IR continuum reveals two infrared sources, IRS 2 and IRS 7, while the main protostellar core IRAS 18162-2048 remains undetected up to $2.47 \mathrm{μm}$. IRS 7 shows a peculiar Hydrogen Recombination Line Br$γ$ profile with a narrow emission component superimposed on a broad absorption feature, consistent with a B2/B3 zero-age main-sequence star. Extended H$_2$ emission exhibits a `sawtooth' pattern in the excitation diagram, characteristic of UV radiation in a PDR rather than shock excitation. The radiative transfer model Cloudy reproduces the H$_2$ ro-vibrational populations for $T_\mathrm{gas}=600$ K and $n_\mathrm{H}=7.9\times10^3 \mathrm{cm^{-3}}$. VLA X and C bands observations reveal a compact radio source previously reported as a stationary condensation (SC) and coincident with IRS 7. For the first time, we detect IRS 7/SC in mm wavelengths. The spectral index in the 3$-$6 cm and 3.3 mm regime is consistent with optically thin free-free emission. Conclusions: Our near-IR and radio observations reveal that IRS 7/SC is a B2/B3 ZAMS star that has begun to photoionise its environment, giving rise to an extended PDR and a compact \ion{H}{ii} region. The coexistence of this source with the deeply embedded protostar IRAS 18162-2048 and other bubble-like structures in the field, suggests a multigenerational star-forming environment. Future \textit{James Webb Space Telescope} observations targeting the H$_2$ pure rotational lines ($3-28 \mathrm{μm}$) and other HRLs less affected by extinction will be essential to characterise the cooler molecular and ionised gas to fully disclose the formation history of the region. |
| title | Diverse stages of star formation in the IRAS 18162-2048 region. Emergence of UV Feedback |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2512.07604 |