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Detection of the Pairwise Kinematic Sunyaev-Zel'dovich Effect and Pairwise Velocity with DESI DR1 Galaxies and ACT DR6 and Planck CMB Data

Yulin Gong, Patricio A. Gallardo, Rachel Bean, Jenna Moore, Eve M. Vavagiakis, Nicholas Battaglia, Boryana Hadzhiyska, Yun-Hsin Hsu, Jessica Nicole Aguilar, Steven Ahlen, Davide Bianchi, David Brooks, Todd Claybaugh, Rebecca Canning, Mark Devlin, Peter Doel, Axel de la Macorra, Simone Ferraro, Andreu Font-Ribera, Jaime E. Forero-Romero, Enrique Gaztañaga, Gaston Gutierrez, Satya Gontcho A Gontcho, Julien Guy, Klaus Honscheid, Cullan Howlett, R. Henry Liu, Mustapha Ishak, Dick Joyce, Anthony Kremin, Claire Lamman, Michael Levi, Martin Landriau, Marc Manera, Aaron Meisner, Ramon Miquel, Michael D. Niemack, Seshadri Nadathur, Will Percival, Francisco Prada, Graziano Rossi, Bernardita Ried Guachalla, Eusebio Sanchez, Hee-Jong Seo, David Sprayberry, David Schlegel, Cristóbal Sifón, Michael Schubnell, Joseph Harry Silber, Gregory Tarlé, Benjamin Alan Weaver, Rongpu Zhou, Hu Zou

TL;DR

The paper reports a high-significance detection of the pairwise kSZ effect by cross-correlating DESI DR1 LRGs with ACT DR6 and Planck CMB maps, achieving up to 9.3σ for a luminosity-selected subsample. It employs aperture photometry, a pairwise-velocity framework, and linear-theory predictions to extract a mass-averaged optical depth τ̄, while enhancing per-cluster velocity inferences through a gradient-boosted decision tree model trained on simulations. The results show consistent signals across multiple CMB maps, align with Planck cosmology and simulations, and demonstrate a practical path to map the cosmic velocity field via kSZ measurements. This work strengthens kSZ as a robust cosmological probe and paves the way for future, higher-precision velocity studies with upcoming CMB and DESI data.

Abstract

We present a 9.3-sigma detection of the pairwise kinematic Sunyaev-Zeldovich (kSZ) effect by combining a sample of 913,286 Luminous Red Galaxies (LRGs) from the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1) catalog and co-added Atacama Cosmology Telescope (ACT DR6) and Planck cosmic microwave background (CMB) temperature maps. This represents the highest-significance pairwise kSZ measurement to date. The analysis uses three ACT CMB temperature maps: co-added 150 GHz, total frequency maps, and a component-separated Internal Linear Combination (ILC) map, all of which cover 19,000 square degrees of the sky from Advanced ACTPol observations conducted between 2017 and 2022. Comparison of the results of these three maps serves as a consistency check for potential foreground contamination that may depend on the observation frequency. An estimate of the best-fit mass-averaged optical depth is obtained by comparing the pairwise kSZ curve with the linear-theory prediction of the pairwise velocity under the best-fit Planck cosmology, and is compared with predictions from simulations. This estimate serves as a reference point for future comparisons with thermal SZ-derived optical depth measurements for the same DESI cluster samples, which will be presented in a companion paper. Finally, we employ a machine-learning approach trained on simulations to estimate the optical depth for 456,803 DESI LRG-identified clusters within the simulated mass range (greater than about 1e13 solar masses). These are combined with the measured kSZ signal to infer the individual cluster peculiar velocities, providing the opportunity to constrain the behavior of gravity and the dark sector over a range of cosmic scales and epochs.

Detection of the Pairwise Kinematic Sunyaev-Zel'dovich Effect and Pairwise Velocity with DESI DR1 Galaxies and ACT DR6 and Planck CMB Data

TL;DR

The paper reports a high-significance detection of the pairwise kSZ effect by cross-correlating DESI DR1 LRGs with ACT DR6 and Planck CMB maps, achieving up to 9.3σ for a luminosity-selected subsample. It employs aperture photometry, a pairwise-velocity framework, and linear-theory predictions to extract a mass-averaged optical depth τ̄, while enhancing per-cluster velocity inferences through a gradient-boosted decision tree model trained on simulations. The results show consistent signals across multiple CMB maps, align with Planck cosmology and simulations, and demonstrate a practical path to map the cosmic velocity field via kSZ measurements. This work strengthens kSZ as a robust cosmological probe and paves the way for future, higher-precision velocity studies with upcoming CMB and DESI data.

Abstract

We present a 9.3-sigma detection of the pairwise kinematic Sunyaev-Zeldovich (kSZ) effect by combining a sample of 913,286 Luminous Red Galaxies (LRGs) from the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1) catalog and co-added Atacama Cosmology Telescope (ACT DR6) and Planck cosmic microwave background (CMB) temperature maps. This represents the highest-significance pairwise kSZ measurement to date. The analysis uses three ACT CMB temperature maps: co-added 150 GHz, total frequency maps, and a component-separated Internal Linear Combination (ILC) map, all of which cover 19,000 square degrees of the sky from Advanced ACTPol observations conducted between 2017 and 2022. Comparison of the results of these three maps serves as a consistency check for potential foreground contamination that may depend on the observation frequency. An estimate of the best-fit mass-averaged optical depth is obtained by comparing the pairwise kSZ curve with the linear-theory prediction of the pairwise velocity under the best-fit Planck cosmology, and is compared with predictions from simulations. This estimate serves as a reference point for future comparisons with thermal SZ-derived optical depth measurements for the same DESI cluster samples, which will be presented in a companion paper. Finally, we employ a machine-learning approach trained on simulations to estimate the optical depth for 456,803 DESI LRG-identified clusters within the simulated mass range (greater than about 1e13 solar masses). These are combined with the measured kSZ signal to infer the individual cluster peculiar velocities, providing the opportunity to constrain the behavior of gravity and the dark sector over a range of cosmic scales and epochs.

Paper Structure

This paper contains 14 sections, 20 equations, 7 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Data
  3. ACT DR6 data
  4. DESI DR1 data
  5. Methods
  6. Secondary Anisotropies
  7. Pairwise statistic
  8. Mass-averaged optical depth estimate
  9. Peculiar velocity estimation
  10. Results
  11. Pairwise kSZ momentum and mass-averaged optical depth measurements
  12. Pairwise velocity inference
  13. Conclusion
  14. Null test

Figures (7)

  • Figure 1: The redshift distribution, showing the number of LRGs, $N_{gal}$, in the sample from DESI DR1 [blue] analyzed in this work and, as a reference, from SDSS DR15 [orange] studied previously in Calafut:2021wkx.
  • Figure 2: ACT DR6 and DESI sky coverage. Background shows the ACT DR6 150GHz map. Shaded colored region shows the selected DESI region footprint, and color shows the average noise level in the ACT 150 GHz map. Gaps in coverage result of combining the DESI footprint with the point source, and galactic mask as described in Section \ref{['sec:data']}.
  • Figure 3: Measured pairwise kSZ momentum curves for the ILC [black circle], $z < 0.8$ ILC subsample [green], f150 [blue cross], and ftot [orange square] maps, based on sources in nine luminosity-selected galaxy tracer samples. From top to bottom, these samples are: L36, L48, L60, L79, and L98. Two different vertical scales are used, scaled to their respective amplitudes. $1\sigma$ uncertainty error bars obtained through bootstrap analysis are also presented. In this study, we concentrate on scales $r > 20$ Mpc, and consequently shade the region corresponding to $r < 20$ Mpc.
  • Figure 4: Same as Fig. \ref{['fig:Phat_result']}, but for disjoint luminosity samples: L36D, L48D, L60D, and L79D. Two different vertical scales are used, scaled to their respective amplitudes.
  • Figure 5: The normalized likelihoods, $L\propto \exp(-\chi^2)$, for the fitted values of $\bar{\tau}$ using the DR6 ILC [black solid] and its corresponding low redshift subsample [grey dahsed], f150 [blue dashed], and ftot [orange dotted] maps, computed for each of the nine luminosity-based tracer samples. The optical depth derived from the simulations is also presented for reference.
  • ...and 2 more figures