Quasars at the dawn of cosmic time (z>6) are hosted by galaxies with extreme interstellar medium conditions. Recent observations of their molecular gas tracers have revealed massive gas reservoirs capable of simultaneously fueling rapid accretion onto the central supermassive black hole and intense bursts of star formation. Feedback from these processes is thought to regulate the early co-evolution of the galaxy and its SMBH.

Despite this progress, our most reliable estimates of the obscured star formation rates in these systems still rely on unresolved spectral energy distribution fitting of the cold dust modified blackbody emission. Such measurements remain highly uncertain due to sparse sampling of the SED, particularly at shorter rest-frame wavelengths where dust emission peaks.

In M. Costa et al.  2025, we addressed this limitation using a dedicated set of ALMA Band 8 observations specifically designed to probe the peak of the dust emission. We derived robust dust physical properties for a sample of ten quasars at 6<z<7, confirming their strongly starbursting nature. Remarkably, although these systems host extremely luminous AGN that dominate the optical emission, their far-infrared properties closely resemble those of submillimeter galaxies with no clear signatures of AGN activity. This suggests that, even in the presence of a powerful quasar, the galaxy-integrated dust properties are largely shaped by star formation rather than by the AGN itself.

One of the main limitations in studying dust emission is the lack of facilities capable of probing the rest-frame wavelength range between 25 µm and 300 µm. This makes it very difficult to constrain the properties of any potential hot dust component, the emission of which would peak in this regime at essentially all redshifts accessible today. Moreover, current infrared surveys are limited to the data obtained with Herschel and Spitzer, which are no longer operational.

PRIMA is a proposed far-infrared observatory, equipped with a 1.8m diameter mirror and able to perform imaging and spectroscopic studies in the 24−235 μm range. To study and showcase what this mission will be capable to achieve, we worked on a simulated dataset to perform a survey of 1000h on 1 deg2. 

In Traina et al. 2025 we showed that for galaxies up to z = 3, PRIMA will be capable for the first time to constrain the warm dust properties of a two component dust model. At the same time,  it will also be able to increase by a factor ∼10 the number of local (z = 0) galaxies for which we can probe the cold dust temperature, as these measurement are up to date mostly coming from Herschel observations.

For a broader view on what are the goals and capabilities of this project you can find here the PRIMA General Observer Science Book, which gathers 120 contributed science cases which could be performed within the context of the PRIMA GO/GI program.