Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

To maximize the amount of information extracted from cosmological datasets, simulations that accurately represent these observations are necessary. However, traditional simulations that evolve particles under gravity by estimating particle-particle interactions (𝑁-body simulations) are computationally expensive and prohibitive to scale to the large volumes and resolutions necessary for the upcoming datasets. Moreover, modeling the distribution of galaxies typically involves identifying virialized dark matter halos, which is also a time- and memory-consuming process for large 𝑁-body simulations, further exacerbating the computational cost. In this study, we introduce CHARM, a novel method for creating mock halo catalogs by matching the spatial, mass, and velocity statistics of halos directly from the large-scale distribution of the dark matter density field. We develop multistage neural spline flow-based networks to learn this mapping at redshift 𝑧 =0.5 directly with computationally cheaper low-resolution particle mesh simulations instead of relying on the high-resolution 𝑁-body simulations. We show that the mock halo catalogs and painted galaxy catalogs have the same statistical properties as obtained from 𝑁-body simulations in both real space and redshift space. Finally, we use these mock catalogs for cosmological inference using redshift-space galaxy power spectrum, bispectrum, and wavelet-based statistics using simulation-based inference, performing the first inference with accelerated forward model simulations and finding unbiased cosmological constraints with well-calibrated posteriors.

Abstract:

SciPost Submission Detail A Short Introduction to Cosmology and its Current Status

Abstract:

We present an analysis of globular clusters (GCs) of dwarf galaxies in the Perseus galaxy cluster that explores the relationship between dwarf galaxy properties and their GCs. Our focus is on GC numbers (NGC) and GC half-number radii (RGC) around dwarf galaxies, and their relations with host galaxy stellar masses (M∗), central surface brightnesses (µ0), and effective radii (Re). This work is unique due to its large sample size and the absence of pre-selection based on µ0 and RGC for dwarf galaxies. Interestingly, we find that at a given stellar mass, RGC is almost independent of the host galaxy µ0 and Re, while RGC/Re depends on µ0 and Re. Lower surface brightness and diffuse dwarf galaxies show RGC/Re ≈ 1, while higher surface brightness and compact dwarf galaxies show RGC/Re ≈ 1.5–2. This means that for dwarf galaxies of similar stellar mass, the GCs have a similar median extent; however, their distribution is different from the field stars of their host. Additionally, low surface brightness and diffuse dwarf galaxies on average have a higher NGC than high surface brightness and compact dwarf galaxies at any given stellar mass. We also find that ultra-diffuse galaxies (UDGs) and non-UDGs in the sample have a similar RGC, while UDGs have a smaller RGC/Re (typically less than one) and a three to four times higher NGC than non-UDGs. Furthermore, when examining nucleated versus non-nucleated dwarf galaxies, we found that for M∗ > 10⁸ M, nucleated dwarf galaxies seem to have a smaller RGC and RGC/Re, with no significant differences seen between their NGC except at M∗ < 10⁸ M, where the nucleated dwarf galaxies tend to have a higher NGC. Lastly, we explored the stellar-to-halo mass ratio (SHMR) of dwarf galaxies (halo mass based on NGC) and conclude that the Perseus cluster dwarf galaxies follow the expected SHMR at z = 0 extrapolated down to M∗ = 10⁶ M .

Abstract:

We present cosmic shear constraints from the completed Kilo-Degree Survey (KiDS), where the cosmological parameter S 8 ≡ σ 8 √Ω m /0.3 = 0.81 +0.016 −0.021 is found to be in agreement (0.73 σ ) with results from the Planck Legacy cosmic microwave background experiment. The final KiDS footprint spans 1347 square degrees of deep nine-band imaging across the optical and near-infrared (NIR), along with an extra 23-square degrees of KiDS-like calibration observations of deep spectroscopic surveys. Improvements in our redshift distribution estimation methodology, combined with our enhanced calibration data and multi-band image simulations, allowed us to extend our lensed sample out to a photometric redshift of z B ≤ 2.0. Compared to previous KiDS analyses, the increased survey area and redshift depth results in a ∼32% improvement in constraining power in terms of Σ 8 ≡ σ 8 (Ω m /0.3) α = 0.821 +0.014 −0.016 , where α = 0.58 has been optimised to match the revised degeneracy direction of σ 8 and Ω m for our current survey at higher redshift. We adopted a new physically motivated intrinsic alignment (IA) model that jointly depends on the galaxy sample’s halo mass and spectral type distributions, and which is informed by previous direct alignment measurements. We also marginalised over our uncertainty on the impact of baryon feedback on the non-linear matter power spectrum. Compared to previous KiDS analyses, we conclude that the increase seen in S 8 primarily results from our improved redshift distribution estimation and calibration, as well as a new survey area and improved image reduction. Our companion paper presents a full suite of internal and external consistency tests (including joint constraints with other datasets), finding the KiDS-Legacy dataset to be the most internally robust sample produced by KiDS to date.