GO-1-Pro: Mid-Far IR Wide-Field Survey

• GO-1-Pro is a comprehensive mid-to-far infrared survey using PRIMAger aboard PRIMA, covering approximately 25% of the sky with imaging, spectroscopy, and polarimetry.
• It employs hyperspectral imaging (R≈8) for PAH diagnostics and photometry in four polarimetric bands (R≈4) to assess dust, star formation, and AGN activity.
• The survey aims to detect over 7–8 million galaxies up to z≈4, yielding unprecedented statistical insights into cosmic star formation, ISM metallicity, and magnetic field geometry.

GO-1-Pro (π-sr IR Survey) is the flagship General Observer (GO) wide-field program of the PRIMAger instrument aboard the PRIMA (PRobe far-Infrared Mission for Astrophysics) observatory. Scheduled to commence large-scale observations circa 2030, GO-1-Pro constitutes a transformational, $\pi$-steradian (≈25% of the sky, $\approx$10,313 deg²) imaging and spectroscopy survey over the mid- to far-infrared (IR) wavelength range 25–260 μm, delivering simultaneous broad-band polarimetry and R≈8 hyperspectral cubes. These data are designed to unlock statistical, environmental, and astrophysical diagnostics on dust, star formation, active galactic nuclei (AGN), interstellar medium (ISM) metallicity, magnetic field topology, and rare high-redshift populations in an unprecedented statistical and cosmological context (Burgarella et al., 22 Sep 2025).

1. Scientific Objectives and Legacy Scope

GO-1-Pro is architected to address several foundational questions in galaxy evolution and the lifecycle of the interstellar medium across environments and redshift:

1. Mid-Infrared PAH Diagnostics: Resolves broad PAH emission features (rest 6.2, 7.7, 8.6, 11.3 μm) out to $z\lesssim4$ using R≈8 (Δλ/λ) hyperspectral imaging over 25–80 μm. Enables rest-frame line-ratio studies, continuum fitting, and robust derivation of photometric redshifts, gas-phase metallicities, and AGN/starburst decompositions for millions of galaxies.
2. Dust Mass and Star-forming History: Measures far-IR SEDs for ≈8×10⁶ galaxies with high completeness to $z\sim4$ in four bands spanning 80–260 μm. Enables precise determination of SFR, dust mass ($M_\mathrm{dust}$), and characteristic temperatures, with cross-comparison to optical/NIR surveys for population synthesis and mass function evolution.
3. Environmental and Quenching Physics: Uniformly samples large-scale cosmic structure (voids, filaments, clusters). Quantifies how tidal/ram-pressure and harassment affect ISM dust dispersal and the quenching of star formation across mass and density scales.
4. Far-IR Polarimetry and Magnetism: Delivers broad-band (R≈4) polarimetric maps (four bands, 80–260 μm), covering ≳10⁶ galaxies per band at SNR≥5. Enables constraints on dust grain alignment and interstellar magnetic field geometries, a first for statistical extragalactic samples at these scales.
5. Discovery of Rare Objects: Curates unbiased samples of ultraluminous IR galaxies (ULIRGs), strong lenses, and proto-cluster candidates to $z>2.5$, with targeted follow-up using the FIRESS spectrometer.

2. Survey Design and Observing Strategy

GO-1-Pro exploits PRIMAger’s full optical and detector architecture in a two-fold observing mode:

• Survey Footprint: $$A = \pi\ \mathrm{sr} = \pi\times(180/\pi)^2\,\mathrm{deg}^2 \approx 10\,313\,\mathrm{deg}^2$$, corresponding to 25% of the sky.
• Wavelength and Resolution Coverage:
  • PHI (Hyperspectral Imaging): 25–80 μm, $R_{\mathrm{PHI}}=\lambda/\Delta\lambda\approx8$, using linear variable filters (LVFs).
  • PPI (Photometric/Polarimetric Imaging): 80–260 μm, $R_{\mathrm{PPI}}\approx4$, in four broad, linearly polarized bands.
• Mapping Efficiency: Fast boustophedon scanning at $250''/$s covers the entire survey in ≈2059 net on-sky hours (4657 scan legs). Every orbital repetition revisits the ecliptic poles, generating a $\approx$023,000× deeper field overlapping the JWST–HST multiwavelength deep field region.

3. Instrument Capabilities and Performance

PRIMAger’s detector suite is divided into six operational bands, summarized in the table below:

Module	$\approx$1 ($\approx$2m)	$\approx$3	Polarimetry	FWHM ($\approx$4)	FOV ($\approx$5)
PHI1	24–45	8	no	~4.7	3.9×1.3
PHI2	45–84	8	no	~8.7	3.9×1.4
PPI1	92	4	yes	~10.9	4.2×4.2
PPI2	126	4	yes	~14.9	4.2×4.2
PPI3	183	4	yes	~21.7	4.2×4.2
PPI4	235	4	yes	~27.6	4.2×4.1

• Sensitivity (5σ, point source; scan mode at max speed 250''/s):

  $\approx$6 ($\approx$7m)	34.3	64.5	92.0	126.0	172.0	235.0
  $\approx$8 (mJy)	2.54	3.44	0.77	1.09	1.49	2.58

Simultaneous operation of PHI and PPI enables concurrent acquisition of hyperspectral data cubes and polarimetric photometry per sky pixel, with beam-matching optimized at each band.

4. Data Products and Processing Pipeline

GO-1-Pro delivers a multi-tiered data structure:

• Levels 0–3: Raw timelines and calibration $\approx$9 photometric/polarimetric maps and spectral cubes $z\lesssim4$0 matched source catalogs.

• Source Extraction: Advanced probabilistic, positionally- and flux-informed de-blending (XID+) to reach flux limits below traditional confusion noise.
• Spectral Analysis: Bayesian SED fitting (CIGALE) of PAH line strengths, continuum parameters ($z\lesssim4$1, $z\lesssim4$2, $z\lesssim4$3), and photometric redshifts, with typical $z\lesssim4$4.
• Polarimetric Analysis: Construction of $z\lesssim4$5 maps yielding per-source polarization fraction $z\lesssim4$6 and angle $z\lesssim4$7.

Every data-processing step accommodates the broad dynamic range and crowding regime required of extragalactic IR survey science.

5. Scientific Yield and Statistical Power

• Galaxy Counts: SIDES semi-empirical simulations forecast detection of $z\lesssim4$8 galaxies to $z\lesssim4$9, rising to $z\sim4$0 to $z\sim4$1 with deep blending priors.
• Polarimetric Yield: Tens of thousands of galaxies reach SNR≥5 in each PPI band, supporting the first population-level constraints on dust polarization properties to cosmological redshift.
• Spectroscopic Diagnostics: PAH and continuum features permit robust in-situ measurements of SFR, metallicity, and AGN fractions, supplementing and calibrating photometric studies.
• Rare Population Discovery: The large, contiguous area offers strong selection for rare luminous, lensed, or clustered galaxies for comprehensive follow-up.

6. Broader Implications and Prospects

GO-1-Pro establishes a new empirical foundation for extragalactic IR astrophysics by integrating hyperspectral PAH mapping and polarized dust emission at uniform depth and area. Its data set is expected to reshape the empirical basis for:

• Cosmic star-formation and dust mass history beyond $z\sim4$2
• Statistical models of large-scale magnetic fields and dust grain physics
• The environmental dependence of galaxy evolution, quenching, and feedback
• Multi-observatory synergy—deep PRIMA pole fields enable cross-calibration against JWST, HST, Euclid, and Roman
• Legacy catalogs in both photometric redshift and polarization, publicly accessible to the community

The performance estimates, survey design, expected yields, and legacy impact are derived from Burgarella et al. (2024) and the PRIMAger GO documentation (Burgarella et al., 22 Sep 2025). GO-1-Pro's combination of sky area, spectro-polarimetric depth, and statistical completeness is without precedent in the mid-to-far IR survey domain.