Lyα spectrum regulated by the cold interstellar medium surrounding H II regions

Studying the amount and kinematics of circumand intergalactic medium (CGM and IGM) is key to understanding the role of feedback and environment (cold streams and galactic winds) in the evolution of galaxies. In particular, $Ly{\alpha}$ emission line has been utilized to investigate the density structure and kinematics of the (most abundant) H I gas in the CGM and IGM around galaxies. Therefore, modeling $Ly{\alpha}$ radiative transfer through multiphase interstellar medium (ISM), CGM and IGM is crucial in understanding the galaxy evolution. As discussed in Kakiichi & Dijkstra (2018), most $Ly{\alpha}$ RT effects would occur on interstellar scales. This is because the main source of $Ly{\alpha}$ photons would be H II regions, which are in most cases, if not all, surrounded by "cold" photo-dissociation regions. However, most $Ly{\alpha}$ RT studies have been performed in the CGM and IGM environments with T ~ 10,000K. In this talk, we present how the $Ly{\alpha}$ RT effect in the cold ISM with T ~ 100 K regulates the $Ly{\alpha}$ spectral properties.