Speaker
Description
I present results from a new local approach to detecting and characterizing Baryon Acoustic Oscillations (BAO) in the large-scale distribution of matter. The possibility of observing individual BAO structures in configuration space was long speculative until the Hoʻoleilana candidate (Tully et al. 2023), discovered in the Cosmicflows-4 dataset, revealed a single shell-like over-density with BAO-scale radius. That discovery raised the question of whether such features are reproducible cosmological signatures or rare fluctuations, and highlighted the need for systematic searches in much larger and deeper surveys. Our work addresses this question by exploiting the unprecedented statistical power of modern datasets to confirm the standard BAO shell and to identify individual instances with high confidence.
We apply a spherical wavelet transform (Arnalte-Mur et al. 2012) to galaxy redshift catalogs, convolving them with shell-shaped filters anchored on cluster centers identified in the DESI Legacy Surveys optical cluster catalog with combined spec- and photo-z (Wen & Han 2024), and tracing surrounding structure with spectroscopic redshifts from DESI DR1. Our analysis focuses on the best-observed regions of DR1 and on the luminous red galaxy samples LRG1 (0.4 < z < 0.6) and LRG2 (0.6 < z < 0.8), using of order 100,000 clusters as anchors for potential BAO centers. Extensive tests against dedicated mock and randomized catalogs, constructed to reproduce the observational properties of both cluster and galaxy samples while excluding BAO physics, enable us to detect the ensemble BAO shell signal in configuration space with significance greater than 5σ. Building on this validation, we assemble a catalog of individual BAO candidates, each with local significances exceeding 5σ. The resulting sample comprises roughly one thousand large-scale shell-like structures, with about five hundred candidates in each redshift bin, and statistical strength comparable to or greater than Hoʻoleilana, demonstrating that localized BAO features are a reproducible aspect of the cosmic density field rather than isolated curiosities.
Rather than replacing the traditional two-point correlation function (2PCF), our method provides a complementary, object-based description of BAO. While the 2PCF yields a volume-averaged acoustic scale, the wavelet approach delivers localized measurements of centers, radii, and radial profiles, enabling direct studies of environmental dependence, anisotropies, and redshift evolution. This localized characterization opens new possibilities for cosmological inference, including consistency tests, independent probes of H(z) and H0 from stacked and individual BAO detections, tests of large-scale homogeneity and isotropy, and improved control of systematics associated with spatial averaging.
In this talk, I will present the methodology, representative detections of both stacked and individual BAO shells, the statistical validation framework, and the implications of localized BAO measurements for future large-scale structure analyses with DESI, Euclid, 4MOST, and related surveys.