Census of the most obscured galaxy nuclei over cosmic time to be revealed by PRIMA

Journal article, 2025

Characterizing the growth of supermassive black holes (SMBHs) is critical to the evolution of galaxies; however, the majority of this activity is obscured, rendering traditional tracers of active SMBHs, such as in the restframe optical/ultraviolet, ineffective. The mid-infrared has been particularly successful in revealing obscured active galactic nucleus activity; however, much of this work is confined to the local universe due to the lack of a far-infrared (far-IR) telescope with the required sensitivity and wavelength coverage. We demonstrate the effectiveness of PRobe Far-Infrared Mission for Astrophysics (PRIMA), a concept 1.8-m far-IR observatory, to detect and characterize deeply obscured galaxy nuclei over cosmic time. With the PRIMAger instrument covering 25 to 235 μm, we find that we can accurately detect obscured nuclei via the deep silicate absorption at restframe 9.8 μm between z ¼ 2–7. In addition, the FIRESS spectrograph can produce R ∼ 100 spectra of obscured nuclei out to z ∼ 7, detecting polycyclic aromatic hydrocarbons, ices, and ionized and molecular gas. With the large number of deeply obscured nuclei that PRIMA can detect and characterize, such a mission is critical to understand the growth of SMBHs.