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Register a new userPredictions for local PNG bias in the galaxy power spectrum and bispectrum and the consequences for $f_{rm NL}$ constraints
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Alexandre Barreira
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We use hydrodynamical separate universe simulations with the IllustrisTNG model to predict the local primordial non-Gaussianity (PNG) bias parameters $b_{phi}$ and $b_{phidelta}$, which enter at leading order in the galaxy power spectrum and bispectrum. This is the first time that $b_{phidelta}$ is measured from either gravity-only or galaxy formation simulations. For dark matter halos, the popular assumption of universality overpredicts the $b_{phidelta}(b_1)$ relation in the range $1 lesssim b_1 lesssim 3$ by up to $Delta b_{phidelta} sim 3$ ($b_1$ is the linear density bias). The adequacy of the universality relation is worse for the simulated galaxies, with the relations $b_{phi}(b_1)$ and $b_{phidelta}(b_1)$ being generically redshift-dependent and very sensitive to how galaxies are selected (we test total, stellar and black hole mass, black hole mass accretion rate and color). The uncertainties on $b_{phi}$ and $b_{phidelta}$ have a direct, often overlooked impact on the constraints of the local PNG parameter $f_{rm NL}$, which we study and discuss. For a survey with $V = 100{rm Gpc}^3/h^3$ at $z=1$, uncertainties $Delta b_{phi} lesssim 1$ and $Delta b_{phidelta} lesssim 5$ around values close to the fiducial can yield relatively unbiased constraints on $f_{rm NL}$ using power spectrum and bispectrum data. We also show why priors on galaxy bias are useful even in analyses that fit for products $f_{rm NL} b_{phi}$ and $f_{rm NL} b_{phidelta}$. The strategies we discuss to deal with galaxy bias uncertainties can be straightforwardly implemented in existing $f_{rm NL}$ constraint analyses (we provide fits for some of the bias relations). Our results motivate more works with galaxy formation simulations to refine our understanding of $b_{phi}$ and $b_{phidelta}$ towards improved constraints on $f_{rm NL}$.
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We revise the Non-Gaussianity of canonical curvaton scenario with a generalized $delta N$ formalism, in which it could handle the generic potentials. In various curvaton models, the energy density is dominant in different period including the secondary inflation of curvaton, matter domination and radiation domination. Our method could unify to deal with these periods since the non-linearity parameter $f_{rm NL}$ associated with Non-Gaussianity is a function of equation of state $w$. We firstly investigate the most simple curvaton scenario, namely the chaotic curvaton with quadratic potential. Our study shows that most parameter space satisfies with observational constraints. And our formula will nicely recover the well-known value of $f_{rm NL}$ in the absence of non-linear evolution. From the micro origin of curvaton, we also investigate the Pseudo-Nambu-Goldstone curvaton. Our result clearly indicates that the second short inflationary process for Pseudo-Nambu-Goldstone curvaton is ruled out in light of observations. Finally, our method sheds a new way for investigating the Non-Gaussianity of curvaton mechanism, espeically for exploring the Non-Gaussianity in MSSM curvaton model.
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We investigate the impact of different assumptions in the modeling of one-loop galaxy bias on the recovery of cosmological parameters, as a follow up of the analysis done in the first paper of the series at fixed cosmology. We use three different synthetic galaxy samples whose clustering properties match the ones of the CMASS and LOWZ catalogues of BOSS and the SDSS Main Galaxy Sample. We investigate the relevance of allowing for either short range non-locality or scale-dependent stochasticity by fitting the real-space galaxy auto power spectrum or the combination of galaxy-galaxy and galaxy-matter power spectrum. From a comparison among the goodness-of-fit ($chi^2$), unbiasedness of cosmological parameters (FoB), and figure-of-merit (FoM), we find that a four-parameter model (linear, quadratic, cubic non-local bias, and constant shot-noise) with fixed quadratic tidal bias provides a robust modelling choice for the auto power spectrum of the three samples, up to $k_{rm max}=0.3,h,mathrm{Mpc}^{-1}$ and for an effective volume of $6,h^{-3},mathrm{Gpc}^3$. Instead, a joint analysis of the two observables fails at larger scales, and a model extension with either higher derivatives or scale-dependent shot-noise is necessary to reach a similar $k_{rm max}$, with the latter providing the most stable results. These findings are obtained with three, either hybrid or perturbative, prescriptions for the matter power spectrum, texttt{RESPRESSO}, gRPT and EFT. In all cases, the inclusion of scale-dependent shot-noise increases the range of validity of the model in terms of FoB and $chi^2$. Interestingly, these model extensions with additional free parameters do not necessarily lead to an increase in the maximally achievable FoM for the cosmological parameters $left(h,,Omega_ch^2,,A_sright)$, which are generally consistent to those of the simpler model at smaller $k_{rm max}$.
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In this paper we use radiative transfer + N-body simulations to explore the feasibility of measurements of cross-correlations between the 21cm field observed by the Square Kilometer Array (SKA) and high-z Lyman Alpha Emitters (LAEs) detected in galaxy surveys with the Subaru Hyper Supreme Cam (HSC), Subaru Prime Focus Spectrograph (PFS) and Wide Field Infrared Survey Telescope (WFIRST). 21cm-LAE cross-correlations are in fact a powerful probe of the epoch of reionization as they are expected to provide precious information on the progress of reionization and the typical scale of ionized regions at different redshifts. The next generation observations with SKA will have a noise level much lower than those with its precursor radio facilities, introducing a significant improvement in the measurement of the cross-correlations. We find that an SKA-HSC/PFS observation will allow to investigate scales below ~10 Mpc/h and ~60 Mpc/h at z=7.3 and 6.6, respectively. WFIRST will allow to access also higher redshifts, as it is expected to observe spectroscopically ~900 LAEs per square degree and unit redshift in the range 7.5<z<8.5. Because of the reduction of the shot noise compared to HSC and PFS, observations with WFIRST will result in more precise cross-correlations and increased observable scales.
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