Under Pressure: Decoding the Effect of High Densities on Derived Nebular Properties
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arXiv
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| Autori principali: | , , , , , , , , |
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| Natura: | Preprint |
| Pubblicazione: |
2025
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| _version_ | 1866914578752864256 |
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| author | Martinez, Z. Berg, D. A. James, B. L. Arellano-Córdova, K. Z. Stark, D. P. Senchyna, P. Skillman, E. D. Rogers, N. S. J. Chisholm, J. |
| author_facet | Martinez, Z. Berg, D. A. James, B. L. Arellano-Córdova, K. Z. Stark, D. P. Senchyna, P. Skillman, E. D. Rogers, N. S. J. Chisholm, J. |
| contents | Recent JWST observations have uncovered a population of compact, high-redshift ($z>6$) galaxies exhibiting extreme nebular conditions and enhanced nitrogen abundances that challenge standard chemical evolution paradigms. We present a joint UV and optical abundance analysis using a new suite of $\texttt{Cloudy}$ photoionization models covering a wide density range ($n_e=10^2-10^9$ cm$^{-3}$), combined with HST and JWST spectroscopy for a sample of star-forming galaxies across $0.0\lesssim z \lesssim10.6$. We find that assuming uniform, low-density conditions ($n_e\sim10^2$ cm$^{-3}$) in high-density environments ($n_e\sim10^5$ cm$^{-3}$) can bias nebular diagnostics by overestimating $T_e$ (up to 1800 K), overpredicting $\log U$ (by $>1$ dex), and underestimating O/H (up to 0.67 dex), while only modestly inflating N/O. Therefore, robust abundance determinations at high-$z$ require a multi-phase density model. Using this model, we recalculate O/H and N/O abundances for our sample and present the first $\log U$ diagnostics and ICFs for high-ionization UV N lines. We find that the UV tracers systematically overestimate N/O by $\sim0.3-0.4$ dex relative to the optical benchmark. We find that N/O increases with redshift, correlating with both $n_e$ and star formation rate surface density ($\rmΣ_{SFR}$), suggesting that N/O is temporarily enhanced in compact, high-pressure environments. However, the $n_e$ evolution with $z$ is more gradual than the $(1+z)^3$ scaling of virial halo densities, suggesting that $n_e$evolution is shaped by both cosmological structure growth and baryonic processes. These trends point to prompt N/O enrichment potentially driven by very massive stars, with key implications for interpreting UV emission and determining reliable chemical abundances from JWST observations of the early universe. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2510_21960 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Under Pressure: Decoding the Effect of High Densities on Derived Nebular Properties Martinez, Z. Berg, D. A. James, B. L. Arellano-Córdova, K. Z. Stark, D. P. Senchyna, P. Skillman, E. D. Rogers, N. S. J. Chisholm, J. Astrophysics of Galaxies Recent JWST observations have uncovered a population of compact, high-redshift ($z>6$) galaxies exhibiting extreme nebular conditions and enhanced nitrogen abundances that challenge standard chemical evolution paradigms. We present a joint UV and optical abundance analysis using a new suite of $\texttt{Cloudy}$ photoionization models covering a wide density range ($n_e=10^2-10^9$ cm$^{-3}$), combined with HST and JWST spectroscopy for a sample of star-forming galaxies across $0.0\lesssim z \lesssim10.6$. We find that assuming uniform, low-density conditions ($n_e\sim10^2$ cm$^{-3}$) in high-density environments ($n_e\sim10^5$ cm$^{-3}$) can bias nebular diagnostics by overestimating $T_e$ (up to 1800 K), overpredicting $\log U$ (by $>1$ dex), and underestimating O/H (up to 0.67 dex), while only modestly inflating N/O. Therefore, robust abundance determinations at high-$z$ require a multi-phase density model. Using this model, we recalculate O/H and N/O abundances for our sample and present the first $\log U$ diagnostics and ICFs for high-ionization UV N lines. We find that the UV tracers systematically overestimate N/O by $\sim0.3-0.4$ dex relative to the optical benchmark. We find that N/O increases with redshift, correlating with both $n_e$ and star formation rate surface density ($\rmΣ_{SFR}$), suggesting that N/O is temporarily enhanced in compact, high-pressure environments. However, the $n_e$ evolution with $z$ is more gradual than the $(1+z)^3$ scaling of virial halo densities, suggesting that $n_e$evolution is shaped by both cosmological structure growth and baryonic processes. These trends point to prompt N/O enrichment potentially driven by very massive stars, with key implications for interpreting UV emission and determining reliable chemical abundances from JWST observations of the early universe. |
| title | Under Pressure: Decoding the Effect of High Densities on Derived Nebular Properties |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2510.21960 |