CHAMPS: Data Reduction and Detection of ~3300 Dusty Galaxies at 1.2 mm

CHAMPS, the COSMOS High-z ALMA-MIRI Population Survey, is the largest ALMA blank-field survey to date, covering 0.2 deg². It observed at a central frequency of 250 GHz (1.2 mm) with 7.5 GHz of bandwidth, targeting the JWST/NIRCam+MIRI footprint in the COSMOS field and exploiting the field's extensive multiwavelength ancillary data from X-ray to radio.

The survey's data reduction achieved good sensitivity: 90% of the survey area reaches depths at or below 200 µJy beam⁻¹, with an average RMS of 146 µJy beam⁻¹. The reduced CHAMPS mosaic has a beam size of θ_res = 1.1″ × 1.1″.

Sources were identified through two detection methods: a blind search for high-SNR sources and a prior-based search using MIRI detections to find faint sources. The blind search produced 595 sources down to SNR ≥ 4.5σ, while the prior catalog produced 3,162 sources down to SNR ≥ 3σ, yielding a full sample of 3,355 unique objects across both catalogs. From these, 385 unique SNR ≥ 5σ sources were identified; after excluding 9 likely spurious edge detections, the robust science sample contains 376 sources above ≥ 5σ.

For this robust sample, the median redshift is ⟨z_1.2mm⟩ = 2.54 (+0.89, −1.69), based on optical/near-IR/mid-IR photometric redshifts and high-quality spectroscopic redshifts, and the median stellar mass is ⟨log(M⋆/M☉)⟩ = 10.79 (+0.42, −3.08). The team also identified 68 of the 376 sources (~18%) as candidate AGN using X-ray, UV-optical, infrared, and radio selection techniques. These catalogs and measurements provide a large statistical basis for future studies of dusty galaxy evolution and AGN activity in the COSMOS field.