Dr. Edmund Christian Herenz

Stellar- and nebular light from galaxies experience different dust attentuation. This is because sightlines towards nebular and stellar light pass through different dust conglomerations in the interstellar medium. A widely cited result for star-forming galaxies in the local universe states that nebular attenuation is approximately twice as large as stellar attenuation (Calzetti's law). However, the universality of Calzetti's law is being scrutinized, as especially young galaxies at high redshift often show a ratio close to unitiy. In this journal club we will discuss a recent pre-print by Jie Song and colleagues. This study performs the to-date largest coherent census of continuum and nebular dust attenuation from z~0-7 using publicly available SDSS and JWST data. Song et al. report no redshift evolution of the average nebular- and stellar attenuation at fixed stellar mass M¿¿¿¿. But, a a mass dependence for the ratio of nebular to stellar extinction emerges: a ratio close to unity is favoured for low-mass galaxies [log(M¿¿¿¿/M¿) < 9], while Calzetti's law is retained in galaxies of higher-mass. This result is interpreted in a two-component dust-framework, where the overall population of young stars and HII regions in less evolved galaxies are more homogenously intermixed, while a significant fraction of massive stars in more evolved galaxies have diffused out of their nascent birth clouds. For the non-extragalctic specialists, I will provide a brief primer of attenuation (measurements and theory) in galaxies. I will also highlight the importance of precise extinction measurements for various aspects of extragalactic astrophysics, and contextualise the Song et al. work with other recent findings by JWST.