Prof. David Alonso

Abstract:

Stacking (i.e., averaging) the value of a given astrophysical field around sources allows us to detect new cosmological signatures, such as the kinematic Sunyaev-Zel’dovich, and gain insight on the astrophysical properties of galaxies and their environment. Further information may be gained by orienting these stacks along preferred axes defined by a local directed field, such as the transverse galaxy velocities, galaxy shapes, or the local tidal forces. Examples of this are searches for the moving lens effect, the detection of dipole signatures, or the study of cosmic filaments. Here we show that all directional stacking signals may be reconstructed, without loss of information, in terms of the cross-power spectrum between the quantity of interest and the $E$ and $B$ modes of the spin field used to define the preferred axes weighted by the local galaxy density. The power spectrum approach has several practical advantages, in terms of speed, finite-resolution effects, data visualization, and combination with other cosmological probes. We also argue that, in some cases, such as stacking using velocities or tidal forces reconstructed from the density field, the recovered signal may be dominated by information that is already present in the cross-spectrum between the target field and the galaxy overdensity itself.

Abstract:

Fast radio bursts (FRBs) probe baryons permeating the cosmic web through their dispersion measures (DMs), which encode the integrated electron density along cosmological sight lines. Using 3455 unique FRB sources from CHIME/FRB with ∼15′ localizations, we present an anthology of DM correlations with tracers of large-scale structure and baryonic matter at redshifts z ≲ 1.5. We measured correlations with a vector signal-to-noise ratio (SNR) of 2.4–5 with 10 probes, including galaxies (2.8), weak gravitational lensing (2.6), cosmic infrared background (4.0), cosmic microwave background (CMB) lensing (3.3), the thermal Sunyaev–Zel’dovich (tSZ) effect (3.8), X-ray emission tracing galaxy clusters (5.0) and superclusters (3.3), soft X-ray background (SXRB, 4.1), and radio continuum emission (3.0). These measurements reveal a consistent picture in which FRB sight lines intersecting overdense environments carry systematically larger DMs. Correlations with hot-gas tracers provide additional leverage on the strength of feedback, as they are strongly weighted toward the dense, bound gas. The measured amplitude of tSZ×DM and SXRB×DM correlations is consistent with theoretical predictions of baryon distribution from a DM–z relation-inferred model with moderate feedback at a ∼0.5σ level. A weaker feedback scenario is disfavored at ∼3.5σ by the SXRB×DM correlation under our adopted modeling assumptions. Taken together, these measurements constitute a quantitative multitracer foundation for a new era in which FRBs from next-generation facilities, such as BURSTT, CHORD, the Deep Synoptic Array, and the Square Kilometer Array, in harmony with other probes, will map the baryon content of the full extent of the cosmic web.