Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

<jats:p>We present a harmonic-space estimator for the cross-correlation between the kinematic Sunyaev-Zel’dovich (kSZ) effect and the reconstructed galaxy momentum field that offers several practical advantages over the traditional stacking approach. The estimator is easy to deploy using relatively modest computational resources and recovers all information available in the galaxy-kSZ cross-correlation. In particular, by using well-understood power spectrum estimation techniques, its statistical uncertainties, including potential correlated uncertainties with other large-scale structure observables, can be easily and accurately estimated. Moreover, standard kSZ stacking measurements can be reconstructed exactly from the estimator at a lower computational cost, employing harmonic-space, catalog-level techniques to recover all small-scale information.</jats:p>

Abstract:

Abstract:

We study the projected clustering of photometric luminous red galaxies from the DESI Legacy Survey, combining their angular power spectrum, bispectrum, and cross-correlation with maps of the CMB lensing convergence from the Planck satellite. We employ a perturbative bias expansion in Eulerian space to describe the clustering of galaxies, modelling the power spectrum and bispectrum at one-loop and tree level, respectively. This allows us to use the bispectrum to self-consistently calibrate the perturbative bias parameters. We validate this model against an N-body simulation, and show that it can be used up to scales of at least kP max ≃ 0.2 h Mpc-1 and kB max ≃ 0.08 h Mpc-1, saturating the information recovered from the data. We obtain constraints on the amplitude of matter fluctuations σ 8 = 0.761 ± 0.020 and the non-relativistic matter fraction Ω m = 0.307 ± 0.015, as well as the combination S 8 ≡ σ 8 √(Ω m /0.3) = 0.769 ± 0.020. Including the galaxy bispectrum leads to a 10–20% improvement on the cosmological constraints, which are also in good agreement with previous analyses of the same data, and in mild tension with Planck at the ∼2.5σ level. Finally, using the bispectrum allows for a substantially more precise measurement of the bias parameters of this sample, which are in reasonable agreement with existing coevolution relations.

Abstract:

We present a multifrequency and multi-instrument methodology to study the physical properties of galaxy clusters and cosmic filaments using cosmic microwave background observations. Our approach enables simultaneous measurement of both the thermal (tSZ) and kinematic Sunyaev–Zeldovich (kSZ) effects, incorporates relativistic corrections, and models astrophysical foregrounds such as thermal dust emission. We do this by jointly fitting a single physical model across multiple maps from multiple instruments at different frequencies, rather than fitting a model to a single Compton-y map. We demonstrate the success of this method by fitting the A399–A401 galaxy cluster pair and filament system using archival data from the Planck satellite and new, targeted deep data from the Atacama Cosmology Telescope, covering 11 different frequencies over 14 maps from 30 GHz to 545 GHz. Our tSZ results are consistent with previous work using Compton-y maps. We measure the line-of-sight peculiar velocities of the cluster–filament system using the kSZ effect and find statistical uncertainties on individual cluster peculiar velocities of ≲600 km s⁻¹, which are competitive with current state-of-the-art measurements. Additionally, we measure the optical depth of the filament component with a signal-to-noise of 8.5σ and reveal hints of its morphology. This modular approach is well-suited for application to future instruments across a wide range of millimeter and submillimeter wavebands.

Abstract:

The division of the Milky Way’s disk into “thin” and “thick” components is a common practice, but one that is often ambiguously defined. The two ways of dividing stars are not equivalent: many stars belonging to the stellar population at high [α/Fe] (the “chemical thick disk”) do not belong to the larger-scale-height exponential density component of G. Gilmore & N. Reid (the “kinematic thick disk”). Furthermore, the existence of two distinct kinematic components is debated. This issue has surfaced in discussions about the recently discovered interstellar object 3I/ATLAS, which likely originated around an old star, and has been variously classified as a member of both the “thin disk” and the “thick disk” by different works. We illustrate that the origins of interstellar objects should be discussed with care, and relative to specific, identified populations of stars.