CMB Lensing |

New paper: multi-probe cosmology with unWISE × ACT DR6 CMB lensing

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

Our paper is now on the arXiv ( ) and submitted to Phys. Rev. D. It builds directly on our 2023 ApJ paper, jointly fitting galaxy auto-correlation, galaxy–lensing cross-correlation, and the CMB lensing auto-spectrum to deliver tighter constraints on structure growth.

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:

DESI Legacy Survey galaxies × ACT DR6 + Planck PR4 lensing
- Sailer et al. ( , JCAP 2024) — cosmological constraints from the cross-correlation
- Kim et al. ( , JCAP 2024) — structure formation over cosmic time
- Qu et al. ( , Phys. Rev. D 2025) — structure growth measurements
Quaia quasars × ACT DR6 + Planck PR4 lensing
- Embil Villagra et al. ( , JCAP 2025) — high-redshift structure growth

DESI × CMB lensing

Fri, 05 Jul 2024 00:00:00 +0000

— the Dark Energy Spectroscopic Instrument — is mapping tens of millions of galaxies and quasars to produce the most detailed redshift survey of the universe to date. Cross-correlating that map with CMB lensing measurements gives us a clean view of how cosmic structure has grown across cosmic time.

I lead the development and deployment of the measurement and analysis pipeline for the DESI DR2 CMB lensing cross-correlation analyses. This is data engineering at scale: galaxy catalogs spanning tens of millions of objects across six distinct samples, CMB lensing maps covering tens of thousands of square degrees, distributed computing pipelines that thread careful systematics control from raw data through to cosmological constraints.

What’s next

The same machinery extends naturally to DESI’s full 5-year dataset and future CMB lensing maps from the Simons Observatory. The pipeline is built to be reusable across galaxy samples, lensing experiments, and parameter spaces.

Detection of the CMB lensing – galaxy bispectrum

Tue, 07 Nov 2023 00:00:00 +0000

A first detection of the three-point cross-correlation between CMB lensing and galaxies, opening a new non-Gaussian probe of large-scale structure beyond what two-point analyses can access. See the project for context.