The ISM properties of ALPINE galaxies as probed by ALMA and JWST: a comprehensive line emission modelling

This thesis aims to model line emission from distinct ISM phases (HII regions and PDRs) detected by the James Webb Space Telescope (JWST) and the Atacama Large Millimeter Array (ALMA) in galaxies at z > 4-5. I used the CLOUDY c22.02 code to develop HII region + PDR models, varying the density (n) ionisation parameter (U) and the metallicity (Z). The incident stellar radiation was modelled using Starburst99 (SB99) and Binary Population and Spectral Synthesis code (BPASS v2.2.1), the last one accounting for binary stars. The models have been validated with VANDELS, VUDS, and CANDELS/SHARDS datasets. After validation, predictions were made for UV/optical lines for the ALPINE galaxies using the observed [CII] 158 um luminosity and SFR, assuming Z = 0.5 Z⊙ and estimating n and U using an analytical model from Ferrara et al. 2019. Results highlighted the impact of binary stars on making harder SED, which affects the HII region + PDR properties and elemental densities in varying star formation histories. I derived relations between the UV/optical predicted lines (CIII],[OIII],Hɑ and [NII]) and the observed SFR for the ALPINE galaxies. These relations revealed strong correlations, notably for CIII] and [NII]. In particular, for CIII]-SFR, I obtained r[SB99,BPASS]=[0.549,0.563] and p-value[SB99,BPASS]=[0.1%,0.09%]. For [NII]-SFR, I obtained r[SB99,BPASS]=[0.689,0.693] and p-value[SB99,BPASS]=[0.00033%,0.00036%]. In conclusion, I predicted the BPT diagram positions for the ALPINE galaxies, that occupy the star-forming galaxies region, as expected from the lack of AGN radiation in my models. However, this analysis shows the sensitivity of BPT diagrams to binary presence, star formation history (SFH), and star formation efficiency (SFE), questioning their reliability in discerning AGN presence in early Universe galaxies. This prompts consideration of the significance of binaries, SFH, and SFE in mimicking AGN signatures in BPT diagrams within the Epoch of Reionization (EoR).