Thermal Map of Galaxy Clusters express
In the frozen desert of Antarctica, the SPT-3G telescope peers deep into the universe. Its target is the ancient microwave radiation left over from the Big Bang. But on its way to us, this radiation passes through giant galaxy clusters filled with scorching gas. The gas slightly warms the photons, and barely visible spots appear on the sky map.
This effect is called the Sunyaev-Zeldovich effect, after the two physicists who predicted it. It works like X-rays, but without X-rays: the hotter the gas, the stronger the distortion. By studying these spots, astronomers learn where clusters are located and how matter is distributed within them. In the new work, they gathered data from several years of observations at 95, 150, and 220 GHz, and also added images from the Herschel space observatory at 600 and 857 GHz. All of this was combined into a single map — the deepest ever created.
The main challenge is separating the desired signal from interference. The most insidious "noise" comes from the cosmic infrared background: light from distant dusty galaxies that also enters the telescope. To remove it, they built two versions of the map: one with maximum sensitivity, the other with the background suppressed. The comparison showed that on the scales of interest, the background is tens of times weaker than the signal. Moreover, the difference between the maps allowed them to measure, for the first time, how the Sunyaev-Zeldovich effect and the infrared background correlate. It turned out that on large scales the correlation is positive — meaning that where there is lots of hot gas, there are also many dusty galaxies. On small scales, the correlation disappears.
This result is not just a technical achievement. It provides new constraints on models describing how galaxies eject matter and energy into their surroundings. Such "feedback" processes are key to understanding the evolution of galaxies and clusters. So the map built in the icy desert helps us see how the entire universe works.
Original abstract
as written by the authors arXiv:2602.10107
We present a measurement of the full shape of the power spectrum of the thermal Sunyaev-Zeldovich (tSZ) effect down to arcminute scales using cosmic microwave background (CMB) data from the South Pole Telescope (SPT) over roughly 100 $${\rm deg}^{2}$$ field. The analysis incorporates data from the 2019/20 seasons of the SPT-3G survey in bands centered at 95, 150, and 220 GHz; from the full SPTpol dataset at 150 GHz; and from {\it Herschel}-SPIRE survey in bands centered at 600 and 857 GHz. We combine data from all the above bands using linear combination (LC) techniques to produce a tSZ or Compton-$$y$$ map. We modify the LC weights to produce multiple versions of the Compton-$$y$$ map, including minimum-variance (MV) and foreground-minimized (-min) maps. We measure the auto- and cross-spectra of a subset of these maps in the range $$\ell \in [500, 5000]$$. While this power spectrum includes contributions from signals other than tSZ, we present numerous checks to show that the most challenging foreground signal, the cosmic infrared background (CIB) is much lower than the desired tSZ signal in the scales of interest in this work. The final tSZ power spectrum is measured at $$9.3\sigma$$ with both the MV and CIB-min maps. Our results are consistent with those reported in other CMB surveys across the literature. Using the difference in the tSZ power spectrum from MV and CIB-min maps, we reconstruct the scale-dependent tSZ-CIB cross-correlation $$\rho_{\ell}^{\rm tSZ \times CIB}$$, finding $$3.1\sigma$$ evidence for a nonzero correlation coefficient that is positive on large scales and approaches zero for $$\ell > 2500$$. This result represents the deepest tSZ maps ever produced and provides new constraints that can help refine astrophysical feedback mechanisms and models of the intracluster medium.
The Sunyaev-Zeldovich effect allows us to see galaxy clusters at vast distances because its brightness does not depend on distance — unlike ordinary light, which fades.
In Carl Sagan's novel "Contact," radio telescopes pick up a signal from a galaxy cluster — maps like this help locate such regions.