A halo model approach to describe clustering and emission of the two main star-forming galaxy populations for cosmic infrared background studies

The cosmic infrared background (CIB), which is traced by the emission from dusty star-forming galaxies, provides a crucial window into the phases of star formation throughout cosmic history. These galaxies, although challenging to detect individually at high redshifts due to their faintness, cumulatively contribute to the CIB, which then becomes a powerful probe of galaxy formation, evolution, and clustering. Here, we introduce a physically motivated model for the CIB emission spanning a wide range of frequency and angular resolution, employing a halo model approach, and distinguishing, within dark matter halos, between two main populations of star-forming galaxies, namely normal late-type spiral and irregular galaxies, and the progenitors of early-type galaxies. The requirement to have two different galaxy populations is motivated by the dichotomy between elliptical and spiral galaxies observed in number counts. The emission from the two galaxy populations maps onto different regimes in frequency and resolution spaces. This allowed us to test an extended two-population CIB model and to constrain its clustering parameters – Mmin, the mass of a halo with 50% probability of having a central galaxy, and α, the power-law index regulating the number of satellite galaxies – through a fit to Planck and Herschel-SPIRE CIB anisotropy measurements. We find that while we were able to place constraints on some of the clustering parameters, the Planck frequency and multipole coverage cannot effectively disentangle the contributions from the two galaxy populations. On the other hand, the Herschel-SPIRE measurements separate out and constrain the clustering of both populations. Nonetheless, our work highlights an inconsistency of the results between the two data sets and therefore we are unable to provide a joint fit. This outcome has already been reported in other literature when fitting a single-population model and is still present in our extended scenario.