Unveiling the nature of [CII] rich galaxies in the Early Universe with JWST observations

Gathering knowledge about high redshift galaxies in order to study their formation and evolution processes is one of the main purpose of modern astrophysics. The goal of this preliminary study is to understand the physical properties of galaxies, and the interplay between stars observed with the James Webb Space Telescope (JWST), dust and molecular gas, traced by [CII] and detected by the Atacama Large Millimeter/submillimeter Array (ALMA). The data set is provided by the ALMA Large Program to INvestigate or ALPINE which observed 118 galaxies in the [CII] − 158 μm line and far infrared (FIR) continuum emission at 4 < z < 6 hence at the end of HI reionization epoch, during a period of rapid mass assembly characterized by strong star formation activity and relevant morphological changes. We investigated a sub-sample of 23 [CII] detected galaxies also observed by the JWST through either the COSMOS-Web or the PRIMER surveys in the COSMOS Legacy Field using the near infrared NIRCam (0.6 − 5 μm) and MIRI (5 − 28 μm) instruments. The first step involves the overlapping of the [CII] ALMA detection over the JWST images at all filters for 3.5σ and 5σ levels. The second stage is the fitting procedure realized for each JWST image. This has been performed in a different way according to the morphology of the galaxy: by eye we divided the data sample in two main groups, one made up of single component galaxies and a second one that showed clearly visible multi-clumps in galaxies. The first group has been studied using the GALFIT software while for the second one we applied a hand-made algorithm by Dr. Matteo Messa but both groups have been subject to an iterative non-linear least squares fitting to find the best fitting model. Associated errors have been calculated with a Montecarlo algorithm. The last phase required the SED fitting procedure, applied in the same way for both groups. Assuming the Yggdrasil stellar population code and the minimum χ2 statistics, we computed the mass for every single clump. The results are that ∼ 61% of the sources are clumpy galaxies while the other ∼ 39% are single component structures. These last ones tends to be more massive, extended and luminous with respect to multi-clumps in galaxies suggesting that they are single star-forming regions within larger low surface brightness galaxies or massive compact objects. On the contrary, multi-clumps show higher SFR compared to low z clumps, giving a hint of strong star formation activity inside the clumps at high z and of a relevant role in the rapid galactic mass assembly. Moreover, clumpy galaxies usually have M < 10^10 M⊙ but larger than 10^9.5 M⊙, in contrast with simulations and advocating for a review of clump formation models.