Spatially resolved [CII]-gas conversion factor in early galaxies
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arXiv
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| Natura: | Preprint |
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2025
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| author | Vallini, L. Pallottini, A. Kohandel, M. Sommovigo, L. Ferrara, A. Bethermin, M. Herrera-Camus, R. Carniani, S. Faisst, A. Zanella, A. Pozzi, F. Dessauges-Zavadsky, M. Gruppioni, C. Veraldi, E. Accard, C. |
| author_facet | Vallini, L. Pallottini, A. Kohandel, M. Sommovigo, L. Ferrara, A. Bethermin, M. Herrera-Camus, R. Carniani, S. Faisst, A. Zanella, A. Pozzi, F. Dessauges-Zavadsky, M. Gruppioni, C. Veraldi, E. Accard, C. |
| contents | Determining how efficiently gas collapses into stars at high-redshift is key to understanding galaxy evolution in the Epoch of Reionization (EoR). Globally, this process is quantified by the gas depletion time ($t_{dep}$); on resolved scales, by the slope and normalization of the Kennicutt-Schmidt (KS) relation. This work explores the global ($α_{[CII]}$) and spatially resolved ($W_{[CII]}$) [CII]-to-gas conversion factors at high-$z$ and their role in inferring reliable gas masses, surface densities, and $t_{dep}$ in the EoR. We select galaxies at 4<z<9 from the SERRA cosmological zoom-in simulation, that features on-the-fly radiative transfer and resolves interstellar medium properties down to $\approx$30 pc. The [CII] emission modelling from photodissociation regions allow us to derive global $α_{ [CII]}$, and maps of $W_{[CII]}$. We study their dependence on gas metallicity (Z), density (n), Mach number (M), and burstiness parameter ($k_s$), and provide best fit relations. The $α_{[CII]}$ decreases with increasing $Z$ and galaxy compactness, while the resolved $W_{[CII]}$ shows two regimes: at $Z< 0.2 Z_\odot$, it anticorrelates with n and Z, but not with $k_s$; above this threshold, it also depends on $k_s$, with more bursty regions showing lower conversion factors. This implies $W_{[CII]}\propto Σ_{[CII]}^{-0.5}$, as dense, metal-rich, and bursty regions exhibit higher [CII] surface brightness. Applying a constant $α_{[CII]}$ overestimates $Σ_{gas}$ in bright $Σ_{[CII]}$ patches, thus flattening the KS slope and overestimating $t_{dep}$ by a factor of $\approx$4. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_14001 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Spatially resolved [CII]-gas conversion factor in early galaxies Vallini, L. Pallottini, A. Kohandel, M. Sommovigo, L. Ferrara, A. Bethermin, M. Herrera-Camus, R. Carniani, S. Faisst, A. Zanella, A. Pozzi, F. Dessauges-Zavadsky, M. Gruppioni, C. Veraldi, E. Accard, C. Astrophysics of Galaxies Determining how efficiently gas collapses into stars at high-redshift is key to understanding galaxy evolution in the Epoch of Reionization (EoR). Globally, this process is quantified by the gas depletion time ($t_{dep}$); on resolved scales, by the slope and normalization of the Kennicutt-Schmidt (KS) relation. This work explores the global ($α_{[CII]}$) and spatially resolved ($W_{[CII]}$) [CII]-to-gas conversion factors at high-$z$ and their role in inferring reliable gas masses, surface densities, and $t_{dep}$ in the EoR. We select galaxies at 4<z<9 from the SERRA cosmological zoom-in simulation, that features on-the-fly radiative transfer and resolves interstellar medium properties down to $\approx$30 pc. The [CII] emission modelling from photodissociation regions allow us to derive global $α_{ [CII]}$, and maps of $W_{[CII]}$. We study their dependence on gas metallicity (Z), density (n), Mach number (M), and burstiness parameter ($k_s$), and provide best fit relations. The $α_{[CII]}$ decreases with increasing $Z$ and galaxy compactness, while the resolved $W_{[CII]}$ shows two regimes: at $Z< 0.2 Z_\odot$, it anticorrelates with n and Z, but not with $k_s$; above this threshold, it also depends on $k_s$, with more bursty regions showing lower conversion factors. This implies $W_{[CII]}\propto Σ_{[CII]}^{-0.5}$, as dense, metal-rich, and bursty regions exhibit higher [CII] surface brightness. Applying a constant $α_{[CII]}$ overestimates $Σ_{gas}$ in bright $Σ_{[CII]}$ patches, thus flattening the KS slope and overestimating $t_{dep}$ by a factor of $\approx$4. |
| title | Spatially resolved [CII]-gas conversion factor in early galaxies |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2504.14001 |