My ADS Library

Multiplet Alignment

Gravitational forces from the largest structures in the universe leave a detectable imprint on galaxies and their local environment. This can manifest as the 'intrinsic alignment' of galaxy orientations to the large-scale tidal field. Although considered a nuisance for weak lensing, these correlations uniquely encode cosmological information sensitive to the physics of the very early universe. However, applications are limited due to the challenges of imaging the shapes of individual galaxies and the fact that alignment is not observed in blue or faint galaxies. We circumvent these issues by instead considering the orientation of small sets of galaxies, or 'multiplets'. Most recently, we've used this method to detect intrinsic gravitational shear on the largest scales yet, over 200 Mpc/h.


Detection with DESI DR1: Full Paper | Accessible Summary
Largest scales with DESI DR2: Full Paper | Accessible Summary
Enhancing with imaging (student paper by Alexus Annika Kumwembe): Full Paper

Intrinsic Alignments

Intrinsic Alignments (IA) refers to physical correlations involving galaxy shapes, galaxy spins, and the underlying cosmic web. Its characterization is an important aspect of modern cosmology, particularly in weak lensing analyses. I collaborated with a team of other IA experts to create a guide to common notations and concepts in the field. This resource is both a reference for those already familiar with IA and designed to introduce someone to the field by drawing from various studies and presenting a collection of IA formalisms, estimators, modeling approaches, alternative notations, and useful references. I have also developed optimal estimators for measuring IA in large spectroscopic surveys, which efficiently capture line-of-sight information while remaining relatively insensitive to redshift-space distortions.


The IA Guide: Full Paper | IA Cheat Sheet
Optimal IA estimators: Full Paper | Accessible Summary

IA as an RSD Bias

IA can significantly affect RSD measurements in large surveys like DESI. This arises due to an orientation bias in DESI’s target selection, which is based on the galaxy light that falls within a fiber aperture. This gives rise to anisotropic clustering in DESI’s galaxy map, mimicking the same patterns used to measure RSD and the growth rate of structure. My work reveals a strong redshift dependence of this bias as fainter, redder galaxies are closer to the selection cut and therefore more affected. It can bias measurements of RSD by about 1%, well above DESI’s required total constraint of around 0.5%. Without my corrections, DESI would underestimate the growth rate of structure, biasing determinations of dark energy’s strength and evolution


Initial Publication: Full Paper | Accessible Summary
With DESI Y1 spectra: Full Paper | Accessible Summary

Miscellaneous

Presenting galactic constellations: charming shapes in large cosmological surveys. We analyze the size of these constellations as an unconventional probe of homogeneity, finding consistency with the cosmological principle and Lambda-CDM. This was a special paper for April 1st, but everything in it is scientifically defensible.


Galactic Constellations in DESI DR1: Full Paper | Galactic Constellations Website