Measurements of the Thermal Sunyaev-Zel'dovich Effect with ACT and DESI Luminous Red Galaxies

TL;DR

This work measures the thermal Sunyaev-Zel'dovich signal around DESI Luminous Red Galaxies using high-resolution ACT DR6 Compton-$y$ maps combined with DESI photometric redshifts across four $z$-bins up to $z\approx1.2$, achieving a $19\sigma$ stacking detection. The analysis employs Compensated Aperture Photometry with a comprehensive masking and filtering pipeline, and critically addresses Cosmic Infrared Background contamination by implementing CIB deprojection and $d\beta$ moment-deprojection, revealing that dust dominates the fiducial maps and that the $d\beta$ approach stabilizes the inferred tSZ profiles with residuals of order $10$–$20\%$. By comparing to IllustrisTNG projections, the study finds evidence for stronger inner-halo feedback than in the simulation, though robust mass calibration and miscentering treatment are required for firmer conclusions. The results advance the understanding of halo gas thermodynamics and baryon content, and set the stage for joint tSZ+kSZ+lensing analyses to constrain feedback processes and baryon distributions in galaxy halos.

Abstract

Cosmic Microwave Background (CMB) photons scatter off the free-electron gas in galaxies and clusters, allowing us to use the CMB as a backlight to probe the gas in and around low-redshift galaxies. The thermal Sunyaev-Zel'dovich effect, sourced by hot electrons in high-density environments, measures the thermal pressure of the target objects, shedding light on halo thermodynamics and galaxy formation and providing a path toward understanding the baryon distribution around cosmic structures. We use a combination of high-resolution CMB maps from the Atacama Cosmology Telescope (ACT) and photometric luminous red galaxy (LRG) catalogues from the Dark Energy Spectroscopic Instrument (DESI) to measure the thermal Sunyaev-Zel'dovich signal in four redshift bins from $z=0.4$ to $z=1.2$, with a combined detection significance of 19$σ$ when stacking on the fiducial CMB Compton-$y$ map. We discuss possible sources of contamination, finding that residual dust emission associated with the target galaxies is important and limits current analyses. We discuss several mitigation strategies and quantify the residual modelling uncertainty. This work complements closely related measurements of the kinematic Sunyaev-Zel'dovich and weak lensing of the same galaxies.

Figures (15)

• Figure 1: Spectroscopic distributions of four sub-sample photometric redshift bins, derived from 2.3 million DESI spectroscopic redshifts. The unit on the $y$ axis is the number of galaxies per square degree within the redshift bin, with width $dz=0.01$.
• Figure 2: Overlap of ACT (black) and DESI (red) observation fields. The overlap area is shown in yellow, and represents the footprint overlap mask. The total overlap area is 7326 square degrees.
• Figure 3: ACT DR6 fiducial $y$-parameter stacked profiles alongside stacked profiles using deprojected CIB $y$-parameter maps with varying values of the $\beta$ parameter. Each panel represents one photometric redshift bin as described in Section \ref{['sec:DESI_Galaxies']}.
• Figure 4: ACT DR6 fiducial $y$-parameter stacked profiles alongside the profiles stacked on $d\beta$ moment-deprojected, CIB-deprojected $y$-parameter maps, with varying values of $\beta$.
• Figure 5: tSZ stacked maps for the fiducial $y$-parameter, CIB deprojected and $d\beta$ deprojected Compton-$y$ maps (at $T_{\rm CIB}=10.70$ K). These stacked maps are not generated using the CAP filter as in the case of the stacked profiles, but through the stacking of image cutouts themselves. Observe the higher noise and artifacts of the $\beta$ deprojected map. We note that through radial averaging, this result is mitigated and that the $d\beta$ deprojection is still capable of producing a signal.