CLASSY VIII: Exploring the Source of Ionization with UV ISM diagnostics in local High-$z$ Analogs
| Autor: | Mingozzi, Matilde, James, Bethan L., Berg, Danielle A., Arellano-Córdova, Karla Z., Plat, Adele, Scarlata, Claudia, Aloisi, Alessandra, Amorín, Ricardo O., Brinchmann, Jarle, Charlot, Stéphane, Chisholm, John, Feltre, Anna, Gazagnes, Simon, Hayes, Matthew, Heckman, Timothy, Hernandez, Svea, Kewley, Lisa J., Kumari, Nimisha, Leitherer, Claus, Martin, Crystal L., Maseda, Michael, Nanayakkara, Themiya, Ravindranath, Swara, Rigby, Jane R., Senchyna, Peter, Skillman, Evan D., Sugahara, Yuma, Wilkins, Stephen M., Wofford, Aida, Xu, Xinfeng |
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| Rok vydání: | 2023 |
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| Druh dokumentu: | Working Paper |
| Popis: | In the current JWST era, rest-frame UV spectra play a crucial role in enhancing our understanding of the interstellar medium (ISM) and stellar properties of the first galaxies in the epoch of reionization (EoR, $z>6$). Here, we compare well-known and reliable optical diagrams sensitive to the main ionization source (i.e., star formation, SF; active galactic nuclei, AGN; shocks) to UV counterparts proposed in the literature - the so-called ``UV-BPT diagrams'' - using the HST COS Legacy Archive Spectroscopic SurveY (CLASSY), the largest high-quality, high-resolution and broad-wavelength range atlas of far-UV spectra for 45 local star-forming galaxies. In particular, we explore where CLASSY UV line ratios are located in the different UV diagnostic plots, taking into account state-of-the-art photoionization and shock models and, for the first time, the measured ISM and stellar properties (e.g., gas-phase metallicity, ionization parameter, carbon abundance, stellar age). We find that the combination of C III] $\lambda\lambda$1907,9 He II $\lambda1640$ and O III] $\lambda$1666 can be a powerful tool to separate between SF, shocks and AGN at sub-solar metallicities. We also confirm that alternative diagrams without O III] $\lambda$1666 still allow us to define a SF-locus with some caveats. Diagrams including C IV $\lambda\lambda$1548,51 should be taken with caution given the complexity of this doublet profile. Finally, we present a discussion detailing the ISM conditions required to detect UV emission lines, visible only in low gas-phase metallicity (12+log(O/H) $\lesssim8.3$) and high ionization parameter (log($U$) $\gtrsim-2.5$) environments. Overall, CLASSY and our UV toolkit will be crucial in interpreting the spectra of the earliest galaxies that JWST is currently revealing. Comment: 36 pages, 15 figures, accepted for publication in ApJ |
| Databáze: | arXiv |
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