PHANGS-ML: the universal relation between PAH band and optical line ratios across nearby star-forming galaxies
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| Natura: | Preprint |
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2024
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| author | Baron, Dalya Sandstrom, Karin Sutter, Jessica Hassani, Hamid Groves, Brent Leroy, Adam Schinnerer, Eva Boquien, Médéric Brazzini, Matilde Chastenet, Jérémy Dale, Daniel Egorov, Oleg Glover, Simon Klessen, Ralf Pathak, Debosmita Rosolowsky, Erik Bigiel, Frank Chevance, Mélanie Grasha, Kathryn Hughes, Annie Méndez-Delgado, J. Eduardo Pety, Jérôme Williams, Thomas Hannon, Stephen Sarbadhicary, Sumit |
| author_facet | Baron, Dalya Sandstrom, Karin Sutter, Jessica Hassani, Hamid Groves, Brent Leroy, Adam Schinnerer, Eva Boquien, Médéric Brazzini, Matilde Chastenet, Jérémy Dale, Daniel Egorov, Oleg Glover, Simon Klessen, Ralf Pathak, Debosmita Rosolowsky, Erik Bigiel, Frank Chevance, Mélanie Grasha, Kathryn Hughes, Annie Méndez-Delgado, J. Eduardo Pety, Jérôme Williams, Thomas Hannon, Stephen Sarbadhicary, Sumit |
| contents | The structure and chemistry of the dusty interstellar medium (ISM) are shaped by complex processes that depend on the local radiation field, gas composition, and dust grain properties. Of particular importance are Polycyclic Aromatic Hydrocarbons (PAHs), which emit strong vibrational bands in the mid-infrared, and play a key role in the ISM energy balance. We recently identified global correlations between PAH band and optical line ratios across three nearby galaxies, suggesting a connection between PAH heating and gas ionization throughout the ISM. In this work, we perform a census of the PAH heating -- gas ionization connection using $\sim$700,000 independent pixels that probe scales of 40--150 pc in nineteen nearby star-forming galaxies from the PHANGS survey. We find a universal relation between $\log$PAH(11.3 \mic/7.7 \mic) and $\log$([SII]/H$α$) with a slope of $\sim$0.2 and a scatter of $\sim$0.025 dex. The only exception is a group of anomalous pixels that show unusually high (11.3 \mic/7.7 \mic) PAH ratios in regions with old stellar populations and high starlight-to-dust emission ratios. Their mid-infrared spectra resemble those of elliptical galaxies. AGN hosts show modestly steeper slopes, with a $\sim$10\% increase in PAH(11.3 \mic/7.7 \mic) in the diffuse gas on kpc scales. This universal relation implies an emerging simplicity in the complex ISM, with a sequence that is driven by a single varying property: the spectral shape of the interstellar radiation field. This suggests that other properties, such as gas-phase abundances, gas ionization parameter, and grain charge distribution, are relatively uniform in all but specific cases. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2410_02864 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | PHANGS-ML: the universal relation between PAH band and optical line ratios across nearby star-forming galaxies Baron, Dalya Sandstrom, Karin Sutter, Jessica Hassani, Hamid Groves, Brent Leroy, Adam Schinnerer, Eva Boquien, Médéric Brazzini, Matilde Chastenet, Jérémy Dale, Daniel Egorov, Oleg Glover, Simon Klessen, Ralf Pathak, Debosmita Rosolowsky, Erik Bigiel, Frank Chevance, Mélanie Grasha, Kathryn Hughes, Annie Méndez-Delgado, J. Eduardo Pety, Jérôme Williams, Thomas Hannon, Stephen Sarbadhicary, Sumit Astrophysics of Galaxies The structure and chemistry of the dusty interstellar medium (ISM) are shaped by complex processes that depend on the local radiation field, gas composition, and dust grain properties. Of particular importance are Polycyclic Aromatic Hydrocarbons (PAHs), which emit strong vibrational bands in the mid-infrared, and play a key role in the ISM energy balance. We recently identified global correlations between PAH band and optical line ratios across three nearby galaxies, suggesting a connection between PAH heating and gas ionization throughout the ISM. In this work, we perform a census of the PAH heating -- gas ionization connection using $\sim$700,000 independent pixels that probe scales of 40--150 pc in nineteen nearby star-forming galaxies from the PHANGS survey. We find a universal relation between $\log$PAH(11.3 \mic/7.7 \mic) and $\log$([SII]/H$α$) with a slope of $\sim$0.2 and a scatter of $\sim$0.025 dex. The only exception is a group of anomalous pixels that show unusually high (11.3 \mic/7.7 \mic) PAH ratios in regions with old stellar populations and high starlight-to-dust emission ratios. Their mid-infrared spectra resemble those of elliptical galaxies. AGN hosts show modestly steeper slopes, with a $\sim$10\% increase in PAH(11.3 \mic/7.7 \mic) in the diffuse gas on kpc scales. This universal relation implies an emerging simplicity in the complex ISM, with a sequence that is driven by a single varying property: the spectral shape of the interstellar radiation field. This suggests that other properties, such as gas-phase abundances, gas ionization parameter, and grain charge distribution, are relatively uniform in all but specific cases. |
| title | PHANGS-ML: the universal relation between PAH band and optical line ratios across nearby star-forming galaxies |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2410.02864 |