English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

In the current JWST era, rest-frame UV spectra play a crucial role inenhancing our understanding of the interstellar medium (ISM) and stellarproperties of the first galaxies in the epoch of reionization (EoR, $z>6$).Here, we compare well-known and reliable optical diagrams sensitive to the mainionization source (i.e., star formation, SF; active galactic nuclei, AGN;shocks) to UV counterparts proposed in the literature - the so-called ``UV-BPTdiagrams'' - using the HST COS Legacy Archive Spectroscopic SurveY (CLASSY),the largest high-quality, high-resolution and broad-wavelength range atlas offar-UV spectra for 45 local star-forming galaxies. In particular, we explorewhere CLASSY UV line ratios are located in the different UV diagnostic plots,taking into account state-of-the-art photoionization and shock models and, forthe first time, the measured ISM and stellar properties (e.g., gas-phasemetallicity, ionization parameter, carbon abundance, stellar age). We find thatthe 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 atsub-solar metallicities. We also confirm that alternative diagrams without OIII] $\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 cautiongiven the complexity of this doublet profile. Finally, we present a discussiondetailing the ISM conditions required to detect UV emission lines, visible onlyin low gas-phase metallicity (12+log(O/H) $\lesssim8.3$) and high ionizationparameter (log($U$) $\gtrsim-2.5$) environments. Overall, CLASSY and our UVtoolkit will be crucial in interpreting the spectra of the earliest galaxiesthat JWST is currently revealing.

CLASSY VIII: Exploring the Source of Ionization with UV ISM diagnostics in local High-$z$ Analogs