ACT DR6 main release

Tue, 18 Mar 2025 00:00:00 +0000

The ACT collaboration has released the DR6 maps, power spectra, likelihoods, and the corresponding cosmological constraints — a milestone the collaboration has been building toward for years. The main papers:

(Louis et al.)
(Calabrese et al.)
(Naess et al.)

The Atacama Cosmology Telescope: Multi-probe cosmology with unWISE galaxies and ACT DR6 CMB lensing

Tue, 03 Sep 2024 00:00:00 +0000

A joint multi-probe analysis combining the unWISE galaxy auto-correlation, the galaxy–CMB-lensing cross-correlation, and the CMB lensing auto-spectrum to tighten constraints on structure growth across two redshift bins. See the project for the broader program.

unWISE × ACT DR6 CMB lensing

Tue, 03 Sep 2024 00:00:00 +0000

Cross-correlations between CMB lensing and galaxy surveys are a key piece of my research. In this work we correlate the unWISE infrared galaxy catalog (~500 million galaxies, between about $z \sim 0.2$ and $z \sim 1.6$) with ACT DR6 CMB lensing, extracting information on the physics of cosmic expansion and structure growth.

For this analysis I build a measurement pipeline that carefully treats and verifies a long list of potential systematics — from foregrounds (both galactic and extragalactic) to redshift and modelling systematics. Ultimately, we delivered percent-level precision with a new level of systematic rigor for this type of analysis.

What we’ve shown

The core of this work was presented in two papers:

(arXiv:2309.05659) established the cross-correlation pipeline and measured the amplitude of structure, $S_8$, at intermediate redshift, a regime complementary to galaxy weak lensing and CMB lensing auto-spectra.
(arXiv:2409.02109) extends this to a full joint fit of the galaxy auto-correlation, the cross-correlation, and the CMB lensing auto-spectrum — tightening constraints across multiple redshift slices.

Going beyond these two-point function analyses, we used the unWISE samples for the first detection of the three-point cross-correlation between CMB lensing and galaxies , opening a new non-Gaussian probe of large-scale structure.

Foundational ACT DR6 lensing release

This work sits on top of the ACT DR6 lensing data release, which I contributed to:

Madhavacheril et al. ( ) — DR6 gravitational lensing map and cosmological parameters
Qu et al. ( ) — DR6 CMB lensing power spectrum
MacCrann et al. ( ) — mitigating extragalactic foregrounds

And, more recently, the joint structure-growth analysis combining CMB lensing from ACT, SPT, and Planck:

Qu et al. ( , PRL) — unified structure growth measurements

Other cross-correlationas building on this work

The methodology developed here has been carried over to other galaxy samples I’ve worked on: