arXiv subjects

Nhat-Minh Nguyen

Publications and source records attributed to Nhat-Minh Nguyen.

21 records · Page 2Linked to original sources

arXiv2021

Impacts of the physical data model on the forward inference of initial conditions from biased tracers

We investigate the impact of each ingredient in the employed physical data model on the Bayesian forward inference of initial conditions from biased tracers at the field level. Specifically, we use dark matter halos in a given cosmological simulation volume as tracers of the underlying matter density field. We study the effect of tracer density, grid resolution, gravity model, bias model and likelihood on the inferred initial conditions. We find that the cross-correlation coefficient between true and inferred phases reacts weakly to all ingredients above, and is well predicted by the theoretical expectation derived from a Gaussian model on a broad range of scales. The bias in the amplitude of the inferred initial conditions, on the other hand, depends strongly on the bias model and the likelihood. We conclude that the bias model and likelihood hold the key to an unbiased cosmological inference. Together they must keep the systematics -- which arise from the sub-grid physics that are marginalized over -- under control in order to obtain an unbiased inference.

astro-ph.CO↗

arXiv2020

Taking measurements of the kinematic Sunyaev-Zel'dovich effect forward: including uncertainties from velocity reconstruction with forward modeling

We measure the kinematic Sunyaev-Zel'dovich (kSZ) effect, imprinted by maxBCG clusters, on the Planck SMICA map of the Cosmic Microwave Background (CMB). Our measurement, for the first time, directly accounts for uncertainties in the velocity reconstruction step through the process of Bayesian forward modeling. We show that this often neglected uncertainty budget typically increases the final uncertainty on the measured kSZ signal amplitude by $\simeq15\%$ at cluster scale. We observe evidence for the kSZ effect, at a significance of $\simeq2σ$. Our analysis, when applied to future higher-resolution CMB data, together with minor improvements in map-filtering and signal-modeling methods, should yield both significant and unbiased measurements of the kSZ signal, which can then be used to probe and constrain baryonic content of galaxy clusters and galaxy groups.

astro-ph.CO↗

arXiv2020

Cosmology Inference from Biased Tracers using the EFT-based Likelihood

The effective-field-theory (EFT) approach to the clustering of galaxies and other biased tracers allows for an isolation of the cosmological information that is protected by symmetries, in particular the equivalence principle, and thus is robust to the complicated dynamics of dark matter, gas, and stars on small scales. All existing implementations proceed by making predictions for the lowest-order $n$-point functions of biased tracers, as well as their covariance, and comparing with measurements. Recently, we presented an EFT-based expression for the conditional probability of the density field of a biased tracer given the matter density field, which in principle combines information from arbitrarily high order $n$-point functions. Here, we report results based on this likelihood by applying it to halo catalogs in real space, specifically on the inference of the power spectrum normalization $σ_8$. We include bias terms up to second order as well as the leading higher-derivative term. For a cutoff value of $Λ= 0.1 h\,{\rm Mpc}^{-1}$, we recover the ground-truth value of $σ_8$ to within 95% CL for different halo samples and redshifts. We discuss possible sources for the remaining systematic bias in $σ_8$ as well as future developments.

astro-ph.CO↗