Probing neutral outflows from galaxies at Cosmic Noon using JWST observations of Ca II lines

Outflows from massive high-redshift galaxies driven by AGN activity are thought to be the main responsible for star formation quenching, although direct proofs are still missing. The study of neutral outflows at high redshift are mainly based on the observation of Na I D absorption lines, which are typically blended, preventing a precise inference of gas properties. This thesis extends the neutral gas analysis to a non-blended tracer: the Ca II K and Ca II H absorption lines. The studied sample is composed of 10 JWST/NIRSpec spectra of massive galaxies at Cosmic Noon (z ∼ 2) from the Blue Jay survey. The stellar and dust contributions to the spectra of each galaxy are first modeled with the Prospector code. These best-fit spectra are then used to normalize the total galaxy spectra to isolate the neutral gas absorption. I develop a neutral gas model which produces a synthetic spectrum of the Ca II K, H and Na I D absorption lines given the column density, velocity dispersion and Doppler shift of the lines. The model also includes the nearby He I and Hϵ emission lines that can affect the shape and properties of the absorption lines. The neutral gas parameters are inferred using the emcee code, based on MCMC methods. One of the most important results is that the Ca and Na absorption lines have very similar kinematics, which means that Ca II can be used to trace the same neutral gas outflow probed by the Na I D absorption lines. This has important implications for future studies. Moreover, I analyze the ratio of the Ca and Na column density as a function of galaxy properties, finding a possible trend with respect to their dust attenuation. This could be explained by a higher depletion of Ca atoms onto dust grains compared to Na atoms, consistent with theoretical studies. This work leads to a better understanding of neutral outflows and their role in the suppression of star formation in massive high-redshift galaxies.