arXiv subjects

Alexandre Barreira

Publications and source records attributed to Alexandre Barreira.

At least 19 recordsLinked to original sources

arXiv2023

Towards optimal and robust $f_{\rm NL}$ constraints with multi-tracer analyses

We discuss the potential of the multi-tracer technique to improve observational constraints of the local primordial non-Gaussianity (PNG) parameter $f_{\rm NL}$ from the galaxy power spectrum. For two galaxy samples $A$ and $B$, the constraining power is $\propto |b_1^B b_ϕ^A - b_1^Ab_ϕ^B|$, where $b_1$ and $b_ϕ$ are the linear and PNG galaxy bias parameters. We show this allows for significantly improved constraints compared to the traditional expectation $\propto |b_1^A - b_1^B|$ based on naive universality-like relations where $b_ϕ\propto b_1$. Using IllustrisTNG galaxy simulation data, we find that different equal galaxy number splits of the full sample lead to different $|b_1^B b_ϕ^A - b_1^Ab_ϕ^B|$, and thus have different constraining power. Of all of the strategies explored, splitting by $g-r$ color is the most promising, more than doubling the significance of detecting $f_{\rm NL}b_ϕ\neq 0$. Importantly, since these are constraints on $f_{\rm NL}b_ϕ$ and not $f_{\rm NL}$, they do not require priors on the $b_ϕ(b_1)$ relation. For direct constraints on $f_{\rm NL}$, we show that multi-tracer constraints can be significantly more robust than single-tracer to $b_ϕ$ misspecifications and uncertainties; this relaxes the precision and accuracy requirements for $b_ϕ$ priors. Our results present new opportunities to improve our chances to detect and robustly constrain $f_{\rm NL}$, and strongly motivate galaxy formation simulation campaigns to calibrate the $b_ϕ(b_1)$ relation.

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arXiv2023

Super-sample covariance of the power spectrum, bispectrum, halos, voids, and their cross covariances

We study the effect of super-sample covariance (SSC) on the power spectrum and higher-order statistics: bispectrum, halo mass function, and void size function. We also investigate the effect of SSC on the cross covariance between the statistics. We consider both the matter and halo fields. Higher-order statistics of the large-scale structure contain additional cosmological information beyond the power spectrum and are a powerful tool to constrain cosmology. They are a promising probe for ongoing and upcoming high precision cosmological surveys such as DESI, PFS, Rubin Observatory LSST, Euclid, SPHEREx, SKA, and Roman Space Telescope. Cosmological simulations used in modeling and validating these statistics often have sizes that are much smaller than the observed Universe. Density fluctuations on scales larger than the simulation box, known as super-sample modes, are not captured by the simulations and in turn can lead to inaccuracies in the covariance matrix. We compare the covariance measured using simulation boxes containing super-sample modes to those without. We also compare with the Separate Universe approach. We find that while the power spectrum, bispectrum and halo mass function show significant scale- or mass-dependent SSC, the void size function shows relatively small SSC. We also find significant SSC contributions to the cross covariances between the different statistics, implying that future joint-analyses will need to carefully take into consideration the effect of SSC. To enable further study of SSC, our simulations have been made publicly available at https://github.com/HalfDomeSims/ssc.

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arXiv2023

Cosmology from the integrated shear 3-point correlation function: simulated likelihood analyses with machine-learning emulators

The integrated shear 3-point correlation function $ζ_{\pm}$ measures the correlation between the local shear 2-point function $ξ_{\pm}$ and the 1-point shear aperture mass in patches of the sky. Unlike other higher-order statistics, $ζ_{\pm}$ can be efficiently measured from cosmic shear data, and it admits accurate theory predictions on a wide range of scales as a function of cosmological and baryonic feedback parameters. Here, we develop and test a likelihood analysis pipeline for cosmological constraints using $ζ_{\pm}$. We incorporate treatment of systematic effects from photometric redshift uncertainties, shear calibration bias and galaxy intrinsic alignments. We also develop an accurate neural-network emulator for fast theory predictions in MCMC parameter inference analyses. We test our pipeline using realistic cosmic shear maps based on $N$-body simulations with a DES Y3-like footprint, mask and source tomographic bins, finding unbiased parameter constraints. Relative to $ξ_{\pm}$-only, adding $ζ_{\pm}$ can lead to $\approx 10-25\%$ improvements on the constraints of parameters like $A_s$ (or $σ_8$) and $w_0$. We find no evidence in $ξ_{\pm} + ζ_{\pm}$ constraints of a significant mitigation of the impact of systematics. We also investigate the impact of the size of the apertures where $ζ_{\pm}$ is measured, and of the strategy to estimate the covariance matrix ($N$-body vs. lognormal). Our analysis solidifies the strong potential of the $ζ_{\pm}$ statistic and puts forward a pipeline that can be readily used to improve cosmological constraints using real cosmic shear data.

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arXiv2023

Beyond 3$\times$2-point cosmology: the integrated shear and galaxy 3-point correlation functions

We present the integrated 3-point correlation functions (3PCF) involving both the cosmic shear and the galaxy density fields. These are a set of higher-order statistics that describe the modulation of local 2-point correlation functions (2PCF) by large-scale features in the fields, and which are easy to measure from galaxy imaging surveys. Based on previous works on the shear-only integrated 3PCF, we develop the theoretical framework for modelling 5 new statistics involving the galaxy field and its cross-correlations with cosmic shear. Using realistic galaxy and cosmic shear mocks from simulations, we determine the regime of validity of our models based on leading-order standard perturbation theory with an MCMC analysis that recovers unbiased constraints of the amplitude of fluctuations parameter $A_s$ and the linear and quadratic galaxy bias parameters $b_1$ and $b_2$. Using Fisher matrix forecasts for a DES-Y3-like survey, relative to baseline analyses with conventional 3$\times$2PCFs, we find that the addition of the shear-only integrated 3PCF can improve cosmological parameter constraints by $20-40\%$. The subsequent addition of the new statistics introduced in this paper can lead to further improvements of $10-20\%$, even when utilizing only conservatively large scales where the tree-level models are valid. Our results motivate future work on the galaxy and shear integrated 3PCFs, which offer a practical way to extend standard analyses based on 3$\times$2PCFs to systematically probe the non-Gaussian information content of cosmic density fields.

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arXiv2023

Halo assembly bias from a deep learning model of halo formation

We build a deep learning framework that connects the local formation process of dark matter halos to the halo bias. We train a convolutional neural network (CNN) to predict the final mass and concentration of dark matter halos from the initial conditions. The CNN is then used as a surrogate model to derive the response of the halos' mass and concentration to long-wavelength perturbations in the initial conditions, and consequently the halo bias parameters following the "response bias" definition. The CNN correctly predicts how the local properties of dark matter halos respond to changes in the large-scale environment, despite no explicit knowledge of halo bias being provided during training. We show that the CNN recovers the known trends for the linear and second-order density bias parameters $b_1$ and $b_2$, as well as for the local primordial non-Gaussianity linear bias parameter $b_ϕ$. The expected secondary assembly bias dependence on halo concentration is also recovered by the CNN: at fixed mass, halo concentration has only a mild impact on $b_1$, but a strong impact on $b_ϕ$. Our framework opens a new window for discovering which physical aspects of the halo's Lagrangian patch determine assembly bias, which in turn can inform physical models of halo formation and bias.

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arXiv2023

Constraints on compensated isocurvature perturbations from BOSS DR12 galaxy data

We use the BOSS DR12 galaxy power spectrum to constrain compensated isocurvature perturbations (CIP), which are opposite-sign primordial baryon and dark matter perturbations that leave the total matter density unchanged. Long-wavelength CIP $σ(\vec{x})$ enter the galaxy density contrast as $δ_g(\vec{x}) \supset b_σσ(\vec{x})$, with $b_σ$ the linear CIP galaxy bias parameter. We parameterize the CIP spectra as $P_{σσ} = A^2P_{\mathcal{R}\mathcal{R}}$ and $P_{σ\mathcal{R}} = ξ\sqrt{P_{σσ}P_{\mathcal{R}\mathcal{R}}}$, where $A$ is the CIP amplitude and $ξ$ is the correlation with the curvature perturbations $\mathcal{R}$. We find a significance of detection of $Ab_σ\neq 0$ of $1.8σ$ for correlated ($ξ= 1$) and $3.7σ$ for uncorrelated ($ξ= 0$) CIP. Large-scale data systematics have a bigger impact for uncorrelated CIP, which may explain the large significance of detection. The constraints on $A$ depend on the assumed priors for the $b_σ$ parameter, which we estimate using separate universe simulations. Assuming $b_σ$ values representative of all halos we find $σ_A = 145$ for correlated CIP and $σ_{|A|} = 475$ for uncorrelated CIP. Our strongest uncorrelated CIP constraint is for $b_σ$ representative of the $33\%$ most concentrated halos, $σ_{|A|} = 197$, which is better than the current CMB bounds $|A| \lesssim 360$. We also discuss the impact of the local primordial non-Gaussianity parameter $f_{\rm NL}$ in CIP constraints. Our results demonstrate the power of galaxy data to place tight constraints on CIP, and motivate works to understand better the impact of data systematics, as well as to determine theory priors for $b_σ$.

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arXiv2023

Assembly bias in the local PNG halo bias and its implication for $f_{\rm NL}$ constraints

We use $N$-body simulations to study halo assembly bias (i.e., the dependence of halo clustering on properties beyond total mass) in the density and primordial non-Gaussianity (PNG) linear bias parameters $b_1$ and $b_ϕ$, respectively. We consider concentration, spin and sphericity as secondary halo properties, for which we find a clear detection of assembly bias for $b_1$ and $b_ϕ$. At fixed total mass, halo spin and sphericity impact $b_1$ and $b_ϕ$ in a similar manner, roughly preserving the shape of the linear $b_ϕ(b_1)$ relation satisfied by the global halo population. Halo concentration, however, drives $b_1$ and $b_ϕ$ in opposite directions. This induces significant changes to the $b_ϕ(b_1)$ relation, with higher concentration halos having higher amplitude of $b_ϕ(b_1)$. For $z=0.5$ and $b_1 \approx 2$ in particular, the population comprising either all halos, those with the $33\%$ lowest or those with the $33\%$ highest concentrations have a PNG bias of $b_ϕ\approx 3$, $b_ϕ\approx -1$ and $b_ϕ\approx 9$, respectively. Varying the halo concentration can make $b_ϕ$ very small and even change its sign. These results have important ramifications for galaxy clustering constraints of the local PNG parameter $f_{\rm NL}$ that assume fixed forms for the $b_ϕ(b_1)$ relation. We illustrate the significant impact of halo assembly bias in actual data using the BOSS DR12 galaxy power spectrum: assuming that BOSS galaxies are representative of all halos, the $33\%$ lowest or the $33\%$ highest concentration halos yields $σ_{f_{\rm NL}} = 44, 165, 19$, respectively. Our results suggest taking host halo concentration into account in galaxy selection strategies to maximize the signal-to-noise on $f_{\rm NL}$. They also motivate more simulation-based efforts to study the $b_ϕ(b_1)$ relation of halos and galaxies.

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arXiv2022

Can we actually constrain $f_{\rm NL}$ using the scale-dependent bias effect? An illustration of the impact of galaxy bias uncertainties using the BOSS DR12 galaxy power spectrum

The scale-dependent bias effect on the galaxy power spectrum is a very promising probe of the local primordial non-Gaussianity (PNG) parameter $f_{\rm NL}$, but the amplitude of the effect is proportional to $f_{\rm NL}b_ϕ$, where $b_ϕ$ is the linear PNG galaxy bias parameter. Our knowledge of $b_ϕ$ is currently very limited, yet nearly all existing $f_{\rm NL}$ constraints and forecasts assume precise knowledge for it. Here, we use the BOSS DR12 galaxy power spectrum to illustrate how our uncertain knowledge of $b_ϕ$ currently prevents us from constraining $f_{\rm NL}$ with a given statistical precision $σ_{f_{\rm NL}}$. Assuming different fixed choices for the relation between $b_ϕ$ and the linear density bias $b_1$, we find that $σ_{f_{\rm NL}}$ can vary by as much as an order of magnitude. Our strongest bound is $f_{\rm NL} = 16 \pm 16\ (1σ)$, while the loosest is $f_{\rm NL} = 230 \pm 226\ (1σ)$ for the same BOSS data. The impact of $b_ϕ$ can be especially pronounced because it can be close to zero. We also show how marginalizing over $b_ϕ$ with wide priors is not conservative, and leads in fact to biased constraints through parameter space projection effects. Independently of galaxy bias assumptions, the scale-dependent bias effect can only be used to detect $f_{\rm NL} \neq 0$ by constraining the product $f_{\rm NL}b_ϕ$, but the error bar $σ_{f_{\rm NL}}$ remains undetermined and the results cannot be compared with the CMB; we find $f_{\rm NL}b_ϕ \neq 0$ with $1.6σ$ significance. We also comment on why these issues are important for analyses with the galaxy bispectrum. Our results strongly motivate simulation-based research programs aimed at robust theoretical priors for the $b_ϕ$ parameter, without which we may never be able to competitively constrain $f_{\rm NL}$ using galaxy data.

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arXiv2022

Response approach to the integrated shear 3-point correlation function: the impact of baryonic effects on small scales

The integrated shear 3-point correlation function $ζ_{\pm}$ is a higher-order statistic of the cosmic shear field that describes the modulation of the 2-point correlation function $ξ_{\pm}$ by long-wavelength features in the field. Here, we introduce a new theoretical model to calculate $ζ_{\pm}$ that is accurate on small angular scales, and that allows to take baryonic feedback effects into account. Our model builds on the realization that the small-scale $ζ_{\pm}$ is dominated by the nonlinear matter bispectrum in the squeezed limit, which can be evaluated accurately using the nonlinear matter power spectrum and its first-order response functions to density and tidal field perturbations. We demonstrate the accuracy of our model by showing that it reproduces the small-scale $ζ_{\pm}$ measured in simulated cosmic shear maps. The impact of baryonic feedback enters effectively only through the corresponding impact on the nonlinear matter power spectrum, thereby permitting to account for these astrophysical effects on $ζ_{\pm}$ similarly to how they are currently accounted for on $ξ_{\pm}$. Using a simple idealized Fisher matrix forecast for a DES-like survey we find that, compared to $ξ_{\pm}$, a combined $ξ_{\pm}\ \&\ ζ_{\pm}$ analysis can lead to improvements of order $20-40\%$ on the constraints of cosmological parameters such as $σ_8$ or the dark energy equation of state parameter $w_0$. We find similar levels of improvement on the constraints of the baryonic feedback parameters, which strengthens the prospects for cosmic shear data to obtain tight constraints not only on cosmology but also on astrophysical feedback models. These are encouraging results that motivate future works on the integrated shear 3-point correlation function towards applications to real survey data.

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arXiv2022

The local PNG bias of neutral Hydrogen, ${\rm H_I}$

We use separate universe simulations with the IllustrisTNG galaxy formation model to predict the local PNG bias parameters $b_ϕ$ and $b_{ϕδ}$ of atomic neutral hydrogen, ${\rm H_I}$. These parameters and their relation to the linear density bias parameter $b_1$ play a key role in observational constraints of the local PNG parameter $f_{\rm NL}$ using the ${\rm H_I}$ power spectrum and bispectrum. Our results show that the popular calculation based on the universality of the halo mass function overpredicts the $b_ϕ(b_1)$ and $b_{ϕδ}(b_1)$ relations measured in the simulations. In particular, our results show that at $z \lesssim 1$ the ${\rm H_I}$ power spectrum is more sensitive to $f_{\rm NL}$ compared to previously thought ($b_ϕ$ is more negative), but is less sensitive at other epochs ($b_ϕ$ is less positive). We discuss how this can be explained by the competition of physical effects such as that large-scale gravitational potentials with local PNG (i) accelerate the conversion of hydrogen to heavy elements by star formation, (ii) enhance the effects of baryonic feedback that eject the gas to regions more exposed to ionizing radiation, and (iii) promote the formation of denser structures that shield the ${\rm H_I}$ more efficiently. Our numerical results can be used to revise existing forecast studies on $f_{\rm NL}$ using 21cm line-intensity mapping data. Despite this first step towards predictions for the local PNG bias parameters of ${\rm H_I}$, we emphasize that more work is needed to assess their sensitivity on the assumed galaxy formation physics and ${\rm H_I}$ modeling strategy.

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arXiv2022

Predictions for local PNG bias in the galaxy power spectrum and bispectrum and the consequences for $f_{\rm NL}$ constraints

We use hydrodynamical separate universe simulations with the IllustrisTNG model to predict the local primordial non-Gaussianity (PNG) bias parameters $b_ϕ$ and $b_{ϕδ}$, which enter at leading order in the galaxy power spectrum and bispectrum. This is the first time that $b_{ϕδ}$ is measured from either gravity-only or galaxy formation simulations. For dark matter halos, the popular assumption of universality overpredicts the $b_{ϕδ}(b_1)$ relation in the range $1 \lesssim b_1 \lesssim 3$ by up to $Δb_{ϕδ} \sim 3$ ($b_1$ is the linear density bias). The adequacy of the universality relation is worse for the simulated galaxies, with the relations $b_ϕ(b_1)$ and $b_{ϕδ}(b_1)$ 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 $b_ϕ$ and $b_{ϕδ}$ 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 $Δb_ϕ \lesssim 1$ and $Δb_{ϕδ} \lesssim 5$ 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 $f_{\rm NL} b_ϕ$ and $f_{\rm NL} b_{ϕδ}$. 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 $b_ϕ$ and $b_{ϕδ}$ towards improved constraints on $f_{\rm NL}$.

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arXiv2021

Assembly bias in quadratic bias parameters of dark matter halos from forward modeling

We use the forward modeling approach to galaxy clustering combined with the likelihood from the effective-field theory of large-scale structure to measure assembly bias, i.e. the dependence of halo bias on properties beyond the total mass, in the linear ($b_1$) and second order bias parameters ($b_2$ and $b_{K^2}$) of dark matter halos in $N$-body simulations. This is the first time that assembly bias in the tidal bias parameter $b_{K^2}$ is measured. We focus on three standard halo properties: the concentration $c$, spin $λ$, and sphericity $s$, for which we find an assembly bias signal in $b_{K^2}$ that is opposite to that in $b_1$. Specifically, at fixed mass, halos that get more (less) positively biased in $b_1$, get less (more) negatively biased in $b_{K^2}$. We also investigate the impact of assembly bias on the $b_2(b_1)$ and $b_{K^2}(b_1)$ relations, and find that while the $b_2(b_1)$ relation stays roughly unchanged, assembly bias strongly impacts the $b_{K^2}(b_1)$ relation. This impact likely extends also to the corresponding relation for galaxies, which motivates future studies to design better priors on $b_{K^2}(b_1)$ for use in cosmological constraints from galaxy clustering data.

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arXiv2021

Galaxy bias from forward models: linear and second-order bias of IllustrisTNG galaxies

We use field-level forward models of galaxy clustering and the EFT likelihood formalism to study, for the first time for self-consistently simulated galaxies, the relations between the linear $b_1$ and second-order bias parameters $b_2$ and $b_{K^2}$. The forward models utilize all of the information available in the galaxy distribution up to a given order in perturbation theory, which allows us to infer these bias parameters with high signal-to-noise, even from relatively small volumes ($L_{\rm box} = 205{\rm Mpc}/h$). We consider galaxies from the IllustrisTNG simulations, and our main result is that the $b_2(b_1)$ and $b_{K^2}(b_1)$ relations obtained from gravity-only simulations for total mass selected objects are broadly preserved for simulated galaxies selected by stellar mass, star formation rate, color and black hole accretion rate. We also find good agreement between the bias relations of the simulated galaxies and a number of recent estimates for observed galaxy samples. The consistency under different galaxy selection criteria suggests that theoretical priors on these bias relations may be used to improve cosmological constraints based on observed galaxy samples. We do identify some small differences between the bias relations in the hydrodynamical and gravity-only simulations, which we show can be linked to the environmental dependence of the relation between galaxy properties and mass. We also show that the EFT likelihood recovers the value of $σ_8$ to percent-level from various galaxy samples (including splits by color and star formation rate) and after marginalizing over 8 bias parameters. This demonstration using simulated galaxies adds to previous works based on halos as tracers, and strengthens further the potential of forward models to infer cosmology from galaxy data.

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arXiv2021

Responses of Halo Occupation Distributions: a new ingredient in the halo model & the impact on galaxy bias

Halo occupation distribution (HOD) models describe the number of galaxies that reside in different haloes, and are widely used in galaxy-halo connection studies using the halo model (HM). Here, we introduce and study HOD response functions $R_\mathcal{O}^g$ that describe the response of the HODs to long-wavelength perturbations $\mathcal{O}$. The linear galaxy bias parameters $b_\mathcal{O}^g$ are a weighted version of $b_\mathcal{O}^h + R_\mathcal{O}^g$, where $b_\mathcal{O}^h$ is the halo bias, but the contribution from $R_\mathcal{O}^g$ is routinely ignored in the literature. We investigate the impact of this by measuring the $R_\mathcal{O}^g$ in separate universe simulations of the IllustrisTNG model for three types of perturbations: total matter perturbations, $\mathcal{O}=δ_m$; baryon-CDM compensated isocurvature perturbations, $\mathcal{O}=σ$; and potential perturbations with local primordial non-Gaussianity, $\mathcal{O}\propto f_{\rm NL}ϕ$. Our main takeaway message is that the $R_\mathcal{O}^g$ are not negligible in general and their size should be estimated on a case-by-case basis. For stellar-mass selected galaxies, the responses $R_ϕ^g$ and $R_σ^g$ are sizeable and cannot be neglected in HM calculations of the bias parameters $b_ϕ^g$ and $b_σ^g$; this is relevant to constrain inflation using galaxies. On the other hand, we do not detect a strong impact of the HOD response $R_1^g$ on the linear galaxy bias $b_1^g$. These results can be explained by the impact that the perturbations have on stellar-to-total-mass relations. We also look into the impact on the bias of the gas distribution and find similar conclusions. We show that a single extra parameter describing the overall amplitude of $R_\mathcal{O}^g$ recovers the measured $b_\mathcal{O}^g$ well, which indicates that $R_\mathcal{O}^g$ can be easily added to HM/HOD studies as a new ingredient.

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arXiv2021

The Novel Probes Project -- Tests of Gravity on Astrophysical Scales

We introduce The Novel Probes Project, an initiative to advance the field of astrophysical tests of the dark sector by creating a forum that connects observers and theorists. This review focuses on tests of gravity and is intended to be of use primarily to observers, but also to theorists with interest in the development of experimental tests. It is twinned with a separate review on tests of dark matter self-interactions (Adhikari et al., in prep.). Our focus is on astrophysical probes of gravity in the weak-field regime, ranging from stars to quasilinear cosmological scales. These are complementary to both strong-field tests and background and linear probes in cosmology. In particular, the nonlinear screening mechanisms that are an integral part of viable modified gravity models lead to characteristic signals specifically on astrophysical scales. The constraining power of these signals is not limited by cosmic variance, but comes with the challenge of building robust theoretical models of the nonlinear dynamics of stars, galaxies, clusters and large scale structure. In this review we lay the groundwork for a thorough exploration of the astrophysical regime with an eye to using the current and next generation of observations for tests of gravity. We begin by setting the scene for how theories beyond General Relativity are expected to behave, focusing primarily on screened fifth forces. We describe the analytic and numerical techniques for exploring the pertinent astrophysical systems, as well as the signatures of modified gravity. With these in hand we present a range of observational tests, and discuss prospects for future measurements and theoretical developments.

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arXiv2020

Galaxy bias and primordial non-Gaussianity: insights from galaxy formation simulations with IllustrisTNG

We study the impact that large-scale perturbations of (i) the matter density and (ii) the primordial gravitational potential with local primordial non-Gaussianity (PNG) have on galaxy formation using the IllustrisTNG model. We focus on the linear galaxy bias $b_1$ and the coefficient $b_ϕ$ of the scale-dependent bias induced by PNG, which describe the response of galaxy number counts to these two types of perturbations, respectively. We perform our study using separate universe simulations, in which the effect of the perturbations is mimicked by changes to the cosmological parameters: modified cosmic matter density for $b_1$ and modified amplitude $\mathcal{A}_s$ of the primordial scalar power spectrum for $b_ϕ$. We find that the widely used universality relation $b_ϕ= 2δ_c(b_1 - 1)$ is a poor description of the bias of haloes and galaxies selected by stellar mass $M_*$, which is instead described better by $b_ϕ(M_*) = 2δ_c(b_1(M_*) - p)$ with $p \in [0.4, 0.7]$. This is explained by the different impact that matter overdensities and local PNG have on the median stellar-to-halo-mass relation. A simple model of this impact allows us to describe the stellar mass dependence of $b_1$ and $b_ϕ$ fairly well. Our results also show a nontrivial relation between $b_1$ and $b_ϕ$ for galaxies selected by color and black hole mass accretion rate. Our results provide refined priors on $b_ϕ$ for local PNG constraints and forecasts using galaxy clustering. Given that the widely used universality relation underpredicts $b_ϕ(M_*)$, existing analyses may underestimate the true constraining power on local PNG.

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arXiv2020

Baryonic effects on the matter bispectrum

The large-scale clustering of matter is impacted by baryonic physics, particularly AGN feedback. Modelling or mitigating this impact will be essential for making full use of upcoming measurements of cosmic shear and other large-scale structure probes. We study baryonic effects on the matter bispectrum, using measurements from a selection of state-of-the-art hydrodynamical simulations: IllustrisTNG, Illustris, EAGLE, and BAHAMAS. We identify a low-redshift enhancement of the bispectrum, peaking at $k\sim 3h\,{\rm Mpc}^{-1}$, that is present in several simulations, and discuss how it can be associated to the evolving nature of AGN feedback at late times. This enhancement does not appear in the matter power spectrum, and therefore represents a new source of degeneracy breaking between two- and three-point statistics. In addition, we provide physical interpretations for other aspects of these measurements, and make initial comparisons to predictions from perturbation theory, empirical fitting formulas, and the response function formalism. We publicly release our measurements (including estimates of their uncertainty due to sample variance) and bispectrum measurement code as resources for the community.

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arXiv2020

Compensated Isocurvature Perturbations in the Galaxy Power Spectrum

We investigate the potential of the galaxy power spectrum to constrain compensated isocurvature perturbations (CIPs), primordial fluctuations in the baryon density that are compensated by fluctuations in CDM density to ensure an unperturbed total matter density. We show that CIPs contribute to the galaxy overdensity at linear order, and if they are close to scale-invariant, their effects are nearly perfectly degenerate with the local PNG parameter $f_{\rm nl}$ if they correlate with the adiabatic perturbations. This degeneracy can however be broken by analyzing multiple galaxy samples with different bias parameters, or by taking CMB priors on $f_{\rm nl}$ into account. Parametrizing the amplitude of the CIP power spectrum as $P_{σσ} = A^2P_{\mathcal{R}\mathcal{R}}$ (where $P_{\mathcal{R}\mathcal{R}}$ is the adiabatic power spectrum) we find, for a number of fiducial galaxy samples in a simplified forecast setup, that constraints on $A$, relative to those on $f_{\rm nl}$, of order $σ_{A}/σ_{f_{\rm nl}} \approx 1-2$ are achievable for CIPs correlated with adiabatic perturbations, and $σ_{A}/σ_{f_{\rm nl}} \approx 5$ for the uncorrelated case. These values are independent of survey volume, and suggest that current galaxy data are already able to improve significantly on the tightest existing constraints on CIPs from the CMB. Future galaxy surveys that aim to achieve $σ_{f_{\rm nl}} \sim 1$ have the potential to place even stronger bounds on CIPs.

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