Understanding the Evolution of Black Hole Accretion and Dust out to z=4 with a Deep Imaging Extragalactic Survey with PRIMA

Andreas L. Faisst, Chian-Chou Chen, Laure Ciesla, Carlotta Gruppioni

First listed 2025-09-01 | Last updated 2025-09-01

Abstract

The cosmic evolution of obscured star formation, dust properties and production mechanisms, and the prevalence of dust-obscured AGN out to high redshifts are currently some of the hot topics in astrophysics. While much progress has been made in the early days with Spitzer and Herschel, these facilities have not reached the necessary depths to observe the mid-IR light of high-redshift (z > 3) galaxies. Recently, the James Webb Space Telescope (JWST) has filled in the blue side of the rest-frame mid-IR. The Atacama Large (Sub)Millimeter Array (ALMA), on the other hand, provides excellent sensitivity in the far-IR regime, allowing the study of dust and gas properties at high redshifts. Filling the wavelength gap between JWST and ALMA is crucial to progress our understanding of early galaxy evolution - and this will be an important goal in the next decades. The Probe far-IR Mission for Astrophysics (PRIMA), with sensitive imaging and spectroscopic capabilities at 24-240$μ$m and currently in Phase A study, will achieve this and provide insights into early galaxy evolution, Black Hole growth, and dust production mechanisms. Here we present PRIDES, a possible deep and wide-area survey over 1.6 square-degrees of the COSMOS field with PRIMA to study these science cases.

Short digest

This Concept/Survey paper lays out PRIDES, a 1.6 deg^2 COSMOS-field program with PRIMA to fill the mid‑IR gap (24–240 μm) between JWST and ALMA and trace dust and black‑hole growth out to z≈4. With hyperspectral imaging and spectroscopy, PRIDES will constrain IR SED shapes, dust temperatures, and obscured SFRs while identifying dust‑obscured AGN via PAH and silicate features, detecting mid‑IR emission even beyond z>3. Simulations indicate photometric redshifts from PAH features with accuracy that degrades as the AGN contribution increases, and silicate strengths track AGN hardness. Together, these data will map the fraction of obscured star formation and the prevalence of buried SMBH accretion across environments in COSMOS.

Key figures to inspect

• Figure 1: Check which PAH and silicate rest‑frame windows PRIMA samples at z≈1–4 to see how it truly bridges JWST and ALMA and what diagnostics become accessible at each redshift.
• Figure 2 (left): Read the PRIDES depth curves against Kirkpatrick SED templates and compare to CHAMPS/(Ex)MORA, SCUBA‑2, NIKA2, and legacy Spitzer/Herschel limits to gauge what L_IR and stellar‑mass regimes are newly reachable.
• Figure 2 (right): Inspect the simulated Band‑1 spectra for 0% vs 80% AGN to see how silicate absorption/emission shifts the continuum and features, setting PRIMA’s leverage on obscured AGN fraction.
• Figure 3: Note the PRIDES footprint relative to COSMOS‑Web and HST/ACS to understand synergy and the range of environments (voids to overdensities) sampled for dust/AGN demographics.
• Figure 4: Examine how PAH‑based redshift precision varies with L_IR and AGN fraction to judge redshift reliability for dusty and AGN‑dominated sources.