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

This paper presents a new release of millimeter-wave temperature maps and catalogs (comprising emissive sources and galaxy clusters) from the South Pole Telescope's observations of a 57-square-degree field overlapping the Euclid Deep Field South to enable multiwavelength studies.

Original authors: M. Archipley, A. Hryciuk, L. E. Bleem, K. Kornoelje, M. Klein, A. J. Anderson, B. Ansarinejad, M. Aravena, L. Balkenhol, P. S. Barry, K. Benabed, A. N. Bender, B. A. Benson, F. Bianchini, S. Bocquet

Published 2026-02-11

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CC BY 4.0

Original authors: M. Archipley, A. Hryciuk, L. E. Bleem, K. Kornoelje, M. Klein, A. J. Anderson, B. Ansarinejad, M. Aravena, L. Balkenhol, P. S. Barry, K. Benabed, A. N. Bender, B. A. Benson, F. Bianchini, S. Bocquet, F. R. Bouchet, E. Camphuis, M. G. Campitiello, J. E. Carlstrom, J. Cathey, C. L. Chang, S. C. Chapman, P. Chaubal, P. M. Chichura, A. Chokshi, T. -L. Chou, A. Coerver, T. M. Crawford, C. Daley, T. de Haan, R. P. Deane, K. R. Dibert, M. A. Dobbs, M. Doohan, A. Doussot, D. Dutcher, W. Everett, C. Feng, K. R. Ferguson, K. Fichman, B. Floyd, A. Foster, S. Galli, A. E. Gambrel, R. W. Gardner, F. Ge, N. Goeckner-Wald, A. Gonzalez, S. Grandis, T. R. Greve, R. Gualtieri, F. Guidi, S. Guns, N. W. Halverson, R. Hill, E. Hivon, G. P. Holder, W. L. Holzapfel, J. C. Hood, N. Huang, F. Kéruzoré, A. R. Khalife, L. Knox, M. Korman, C. -L. Kuo, K. Levy, A. E. Lowitz, C. Lu, G. P. Lynch, A. Maniyar, E. S. Martsen, F. Menanteau, M. Millea, J. Montgomery, Y. Nakato, T. Natoli, G. I. Noble, Y. Omori, A. Ouellette, Z. Pan, K. A. Phadke, A. W. Pollak, K. Prabhu, W. Quan, S. Raghunathan, M. Rahimi, A. Rahlin, C. L. Reichardt, C. Reuter, M. Rouble, J. E. Ruhl, E. Schiappucci, A. Simpson, J. A. Sobrin, B. Stalder, A. A. Stark, N. Sulzenauer, C. Tandoi, B. Thorne, C. Trendafilova, C. Umilta, J. D. Vieira, A. Vitrier, D. Vizgan, Y. Wan, A. Weiß, N. Whitehorn, W. L. K. Wu, M. R. Young, J. A. Zebrowski, D. Zhou

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Cosmic Handshake: A Tale of Two Telescopes

Imagine you are trying to solve a massive, high-stakes mystery—like finding a specific person in a crowded, dark stadium.

If you only have a flashlight (which shows you bright, tiny points of light), you might see the person’s shiny watch or a glowing phone, but you won't see the massive crowd they are standing in. If you only have a floodlight (which shows you the whole crowd), you’ll see the mass of people, but you won't be able to pick out the individual person.

To solve the mystery, you need both. This scientific paper describes a "cosmic handshake" between two of the world's most powerful "eyes": the South Pole Telescope (SPT) and the Euclid Space Telescope.

The Players

The South Pole Telescope (The Heat-Seeker): Located in the freezing darkness of Antarctica, this telescope doesn't look at "visible" light like our eyes do. Instead, it looks at millimeter waves—a type of heat signature. It’s like using a thermal camera to find warm bodies in a dark room.
Euclid (The Detail-Seeker): This is a space telescope launched by the European Space Agency. It acts like a high-definition camera, capturing the beautiful, sharp colors of galaxies and stars in the visible and infrared spectrum.

What did they do?

The scientists focused on a specific patch of the sky called the Euclid Deep Field South. They used the South Pole Telescope to take "heat maps" of this area.

Think of it like this: Euclid has taken a high-resolution, color photograph of a forest. The SPT team has now come along and taken a thermal scan of that same forest. By overlaying the two, they can see not just where the trees are, but which ones are burning, which ones are warm, and where the massive, invisible "heat clouds" (galaxy clusters) are hiding.

The "Treasure" They Found

By combining these views, the researchers created two massive "shopping lists" (catalogs) of cosmic objects:

1. The Emissive Source Catalog (The "Bright Sparks")
They found 601 objects that glow brightly in the millimeter-wave spectrum.

The "Radio Stars" (Synchrotron sources): These are like cosmic blowtorches—supermassive black holes shooting out jets of energy.
The "Dusty Galaxies" (DSFGs): These are massive, young galaxies choked with cosmic dust. Because they are so dusty, they are invisible to normal cameras (they are "hidden in the smoke"), but the SPT can see their heat signature perfectly. It’s like seeing the glow of a campfire through a thick fog.

2. The Cluster Catalog (The "Cosmic Cities")
They found 217 "galaxy clusters." A cluster is a massive collection of hundreds or thousands of galaxies held together by gravity.

In the space between these galaxies, there is incredibly hot gas. This gas leaves a "shadow" on the background radiation of the universe (called the Sunyaev-Zel’dovich effect).
The SPT is incredibly good at finding these "shadows." This new list is ten times more detailed than previous maps of this area, providing a much better census of the largest structures in our universe.

Why does this matter?

This isn't just about making lists; it's about understanding the history of the universe.

By seeing both the "heat" (from SPT) and the "light" (from Euclid), astronomers can study how galaxies grow, how black holes influence their surroundings, and how the largest structures in the cosmos formed over billions of years.

It is the first major step in a long-term partnership. It’s like two detectives finally sharing their notes—now, they can solve much bigger crimes than they ever could alone.

Technical Summary: Millimeter-wave observations of Euclid Deep Field South using the South Pole Telescope

Title: Millimeter-wave observations of Euclid Deep Field South using the South Pole Telescope: A data release of temperature maps and catalogs
Authors: M. Archipley et al. (2026)
Journal: Astronomy & Astrophysics (A&A)

1. Problem and Context

The advancement of modern cosmology and extragalactic astrophysics relies heavily on multiwavelength datasets to break degeneracies in source characterization. While the Euclid mission provides high-resolution optical and infrared data, it lacks coverage in the millimeter (mm) regime. Conversely, the South Pole Telescope (SPT), specifically using its third-generation camera (SPT-3G), provides deep millimeter-wave observations but requires complementary optical/infrared data to determine photometric redshifts, stellar masses, and environmental contexts.

The specific goal of this work is to provide a dedicated millimeter-wave dataset that overlaps with the Euclid Deep Field South (EDF-S). This overlap is intended to facilitate joint studies of high-redshift dusty star-forming galaxies (DSFGs), active galactic nuclei (AGNs), and galaxy clusters.

2. Methodology

The study utilizes 20 days of dedicated SPT-3G observations (conducted between October and December 2024) covering a 57-square-degree field.

Instrumental Setup: Observations were performed at three frequencies: 95, 150, and 220 GHz (3.3, 2.0, and 1.4 mm).
Map Making: The researchers processed time-ordered data (TOD) using high-pass and low-pass filters to remove atmospheric noise and aliasing. They applied a "common-mode" filter to mitigate atmospheric signals and deconvolved detector time constants and pointing offsets to improve astrometry.
Signal Extraction (Matched Filtering):
- Emissive Sources: A point-source-finding pipeline used an optimal filter (incorporating the telescope beam and noise covariance) followed by a CLEAN algorithm to remove "ringing" artifacts caused by bright sources.
- Galaxy Clusters: Clusters were identified via the thermal Sunyaev-Zel’dovich (tSZ) effect. The pipeline used a range of spatial templates (isothermal $\beta$ -models) and a frequency-combined minimum variance filter to detect temperature decrements.
Validation and Characterization:
- Redshifts: Photometric redshifts for clusters were estimated using the Multi-Component Matched Filter (MCMF) method, combining DECam Legacy Survey (DECaLS) and WISE data.
- Masses: Cluster masses ( $M_{500c}$ ) were estimated using a significance-mass scaling relation calibrated against previous SPT surveys.

3. Key Contributions

Data Release: The paper provides a comprehensive release of coadded temperature maps, apodization masks, and noise amplitude spectral densities.
Dual-Catalog Construction: The creation of two distinct, high-purity catalogs: an emissive source catalog (point sources) and a cluster catalog (tSZ detections).
Cross-Survey Integration: The work establishes a methodological framework for cross-matching SPT millimeter data with Euclid’s optical/infrared datasets, providing a template for future joint "legacy science" projects.

4. Results

Map Sensitivity: The achieved noise depths were 4.3, 3.8, and 13.2 $\mu$ K-arcmin at 95, 150, and 220 GHz, respectively.
Emissive Source Catalog:
- Contains 601 total objects (334 within the EDF-S).
- Composition: 54% are synchrotron-dominated (primarily AGNs/blazars) and 46% are thermal dust-dominated.
- DSFG Candidates: 210 sources were flagged as high-redshift DSFG candidates, many of which lack counterparts in existing infrared or radio catalogs, demonstrating the unique discovery power of mm-wave surveys.
Galaxy Cluster Catalog:
- Contains 217 cluster candidates (121 within EDF-S).
- Density: 3.81 clusters per square degree, representing an order-of-magnitude improvement in cluster density for this region compared to previous tSZ catalogs.
- Statistics: Median redshift $z = 0.70$ and median mass $M_{500c} = 2.12 \times 10^{14} M_\odot/h_{70}$ .
- Purity/Completeness: The sample is $\sim$ 87% pure at the detection threshold ( $\xi > 4$ ) and $>90\%$ complete for masses above $2.5 \times 10^{14} M_\odot/h_{70}$ at $z > 0.25$ .

5. Significance

This paper marks a critical milestone in the synergy between ground-based millimeter telescopes and space-based optical/infrared observatories. By providing a high-density sample of clusters and dusty galaxies in the Euclid footprint, the study enables:

Precision Cosmology: Using cluster counts and tSZ/lensing profiles to constrain cosmological parameters.
Galaxy Evolution: Studying the "cosmic noon" era ( $1 < z < 2$ ) by observing how environment and AGN activity influence star formation in dense regions.
High-Redshift Discovery: Identifying rare, strongly lensed DSFGs and galaxy protoclusters that are otherwise obscured in optical surveys.