Millimeter-wave observations of Euclid Deep Field South using the South Pole Telescope: A data release of temperature maps and catalogs

Context. The South Pole Telescope third-generation camera (SPT-3G) has observed over 10,000 square degrees of sky at 95, 150, and 220 GHz (3.3, 2.0, 1.4 mm, respectively) and will significantly overlap the ongoing 14,000 square-degree Euclid Wide Survey. The Euclid collaboration recently released Euclid Deep Field South (EDF-S) observations of 23 square degrees at wide field depths in the first quick data release (Q1). Aims. With the goal of releasing complementary millimeter-wave data and encouraging legacy science, we performed dedicated observations of a 57-square-degree field overlapping the EDF-S. Methods. The observing time totaled 20 days, and we reached noise depths of 4.3, 3.8, and 13.2 $μ$K-arcmin at 95, 150, and 220 GHz, respectively. Results. In this work we present the temperature maps and two catalogs constructed from these data. The emissive source catalog contains 601 objects (334 inside EDF-S) with 54% synchrotron-dominated sources and 46% thermal dust emission-dominated sources. The 5$σ$ detection thresholds are 1.7, 2.0, and 6.5 mJy in the three bands. The cluster catalog contains 217 cluster candidates (121 inside EDF-S) with median mass $M_{500c}=2.12 \times 10^{14} M_{\odot}/h_{70}$ and median redshift $z$ = 0.70, corresponding to an order-of-magnitude improvement in cluster density over previous tSZ-selected catalogs in this region (3.81 clusters per square degree). Conclusions. The overlap between SPT and Euclid data will enable a range of multiwavelength studies of the aforementioned source populations. This work serves as the first step toward joint projects between SPT and Euclid and provides a rich dataset containing information on galaxies, clusters, and their environments.

💡 Research Summary

This paper presents a new data release that combines deep millimeter‑wave observations from the South Pole Telescope’s third‑generation camera (SPT‑3G) with the Euclid Deep Field South (EDF‑S) optical/near‑infrared survey. Over a 57 deg² region overlapping EDF‑S, the authors conducted 20 days of dedicated observations between 6 October and 3 December 2024, acquiring 197 individual scans at three frequencies: 95 GHz (3.3 mm), 150 GHz (2.0 mm), and 220 GHz (1.4 mm). The resulting maps achieve noise levels of 4.3, 3.8, and 13.2 µK‑arcmin respectively, roughly twice as deep as the SPT‑3G main survey and sufficient to detect faint extragalactic sources and Sunyaev‑Zel’dovich (SZ) decrements with high fidelity.

The data processing follows the established SPT‑3G pipeline: each scan is calibrated, filtered, and combined using inverse‑variance weighting to produce coadded temperature maps in a Zenithal Equal‑Area (ZEA) projection. An apodization mask down‑weights noisy edges, yielding an effective survey area of 57 deg². The authors also provide beam profiles, noise power spectra, and the filtering kernels used for source and cluster extraction.

Two catalogs are released. The emissive‑source catalog contains 601 detections (334 within the EDF‑S footprint) with 5σ flux limits of 1.7 mJy (95 GHz), 2.0 mJy (150 GHz), and 6.5 mJy (220 GHz). Spectral indices separate the population into 54 % synchrotron‑dominated active galactic nuclei (primarily flat‑spectrum radio quasars) and 46 % thermal‑dust‑dominated galaxies, including luminous and ultra‑luminous infrared galaxies (LIRGs/ULIRGs) and high‑redshift dusty star‑forming galaxies (DSFGs). Positions, multi‑band fluxes, and cross‑matches to external radio and sub‑mm catalogs are provided, enabling direct synergy with Euclid’s VIS and NISP photometry for photometric‑redshift and stellar‑mass studies.

The SZ‑cluster catalog lists 217 candidates (121 inside EDF‑S) identified with a multi‑scale matched‑filter optimized for the arc‑minute SZ signal. The median mass, derived from the Y–M scaling relation adopted in Bleem et al. (2015) under a ΛCDM cosmology (σ₈ = 0.80, Ωₘ = 0.30, h = 0.70), is M₅₀₀c = 2.12 × 10¹⁴ M⊙ h₇₀⁻¹, and the median redshift is z ≈ 0.70. This represents an order‑of‑magnitude increase in cluster surface density (≈3.8 clusters deg⁻²) compared with previous SZ surveys in the same sky region.

The scientific impact of this joint dataset is manifold. Combining the SZ‑derived mass estimates with Euclid’s optical/near‑IR richness and weak‑lensing measurements will improve mass calibration and reduce systematic biases in cosmological analyses. The overlap of DSFGs with Euclid’s deep photometry allows precise determination of their redshifts, star‑formation rates, and dust properties, shedding light on the cosmic star‑formation history at 1 ≲ z ≲ 10. Moreover, the cataloged AGN can be studied in the context of their host‑galaxy environments, probing the interplay between black‑hole activity and large‑scale structure. The authors also note that the data are immediately useful for cross‑correlation studies with forthcoming LSST, Roman, and CMB‑S4 observations, enabling joint constraints on dark energy, neutrino mass, and primordial non‑Gaussianity.

All data products—including the three‑band temperature maps, apodization masks, beam and noise characterizations, source and cluster catalogs, and detailed documentation—are publicly available at https://pole.uchicago.edu/public/data/edfs25/. The paper concludes with a roadmap for future joint analyses, emphasizing the development of a unified pipeline that will exploit the full multi‑wavelength synergy of SPT‑3G, Euclid, and other upcoming surveys to advance both astrophysical and cosmological research.