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Benjamin R. Granett

Publications and source records attributed to Benjamin R. Granett.

At least 19 recordsLinked to original sources
arXiv2022

Measuring the growth of structure by matching dark matter haloes to galaxies with VIPERS and SDSS

We test the history of structure formation from redshift 1 to today by matching galaxies from VIPERS and SDSS with dark matter haloes in the MultiDark SMDPL N-body simulation. We first show that the standard subhalo abundance matching (SHAM) recipe implemented with MultiDark characterizes the clustering of galaxies well both at redshift 0 for SDSS and at redshift 1 for VIPERS. This is an important validation of the SHAM model at high redshift. We then remap the simulation timesteps to test alternative growth histories and infer the growth index $γ=0.6\pm0.3$. This analysis demonstrates the power of using N-body simulations to forward model galaxy surveys for cosmological inference.

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arXiv2021

Does jackknife scale really matter for accurate large-scale structure covariances?

The jackknife method gives an internal covariance estimate for large-scale structure surveys and allows model-independent errors on cosmological parameters. Using the SDSS-III BOSS CMASS sample, we study how the jackknife size and number of resamplings impact the precision of the covariance estimate on the correlation function multipoles and the error on the inferred baryon acoustic scale. We compare the measurement with the MultiDark Patchy mock galaxy catalogues, and we also validate it against a set of log-normal mocks with the same survey geometry. We build several jackknife configurations that vary in size and number of resamplings. We introduce the Hartlap factor in the covariance estimate that depends on the number of jackknife resamplings. We also find that it is useful to apply the tapering scheme to estimate the precision matrix from a limited number of resamplings. The results from CMASS and mock catalogues show that the error estimate of the baryon acoustic scale does not depend on the jackknife scale. For the shift parameter $α$, we find an average error of 1.6%, 2.2% and 1.2%, respectively from CMASS, Patchy and log-normal jackknife covariances. Despite these uncertainties fluctuate significantly due to some structural limitations of the jackknife method, our $α$ estimates are in reasonable agreement with published pre-reconstruction analyses. Jackknife methods will provide valuable and complementary covariance estimates for future large-scale structure surveys.

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arXiv2021

MUSCLE-UPS: Improved Approximations of the Matter Field with the Extended Press-Schechter Formalism and Lagrangian Perturbation Theory

Lagrangian algorithms to simulate the evolution of cold dark matter (CDM) are invaluable tools to generate large suites of mock halo catalogues. In this paper, we first show that the main limitation of current semi-analytical schemes to simulate the displacement of CDM is their inability to model the evolution of overdensities in the initial density field, a limit that can be circumvented by detecting halo particles in the initial conditions. We thus propose `MUltiscale Spherical Collapse Lagrangian Evolution Using Press-Schechter' (muscle-ups), a new scheme that reproduces the results from Lagrangian perturbation theory on large scales, while improving the modelling of overdensities on small scales. In muscle-ups, we adapt the extended Press and Schechter (EPS) formalism to Lagrangian algorithms of the displacement field. For regions exceeding a collapse threshold in the density smoothed at a radius $R$, we consider all particles within a radius $R$ collapsed. Exploiting a multi-scale smoothing of the initial density, we build a halo catalogue on the fly by optimizing the selection of halo candidates. This allows us to generate a density field with a halo mass function that matches one measured in $N$-body simulations. We further explicitly gather particles in each halo together in a profile, providing a numerical, Lagrangian-based implementation of the halo model. Compared to previous semi-analytical Lagrangian methods, we find that muscle-ups improves the recovery of the statistics of the density field at the level of the probability density function (PDF), the power spectrum, and the cross correlation with the $N$-body result.

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arXiv2020

Beyond the Lognormal Approximation: a General Simulation Scheme

We present a public code to generate random fields with an arbitrary probability distribution function (PDF) and an arbitrary correlation function. The algorithm is cosmology-independent, applicable to any stationary stochastic process over a three dimensional grid. We implement it in the case of the matter density field, showing its benefits over the lognormal approximation, which is often used in cosmology for generation of mock catalogues. We find that the covariance of the power spectrum from the new fast realizations is more accurate than that from a lognormal model. As a proof of concept, we also apply the new simulation scheme to the divergence of the Lagrangian displacement field. We find that information from the correlation function and the PDF of the displacement-divergence provides modest improvement over other standard analytical techniques to describe the particle field in the simulation. This suggests that further progress in this direction should come from multi-scale or non-local properties of the initial matter distribution.

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arXiv2019

The Multi-Tracer Optimal Estimator applied to VIPERS

We use mock galaxy data from the VIMOS Public Extragalactic Redshift Survey (VIPERS) to test the performance of the Multi-Tracer Optimal Estimator (MTOE) of Abramo et al. as a tool to measure the monopoles of the power spectra of multiple tracers of the large-scale structure, $P^{(0)}_α(k)$. We show that MTOE provides more accurate measurements than the standard technique of Feldman, Kaiser & Peacock (FKP), independently of the tracer-selection strategy adopted, on both small and large scales. The largest improvements on individual $P^{(0)}_α(k)$ are obtained using a colour-magnitude selection on small scales, due to MTOE being naturally better equipped to deal with shot noise: we report an average error reduction with respect to FKP of $\sim$ 40$\%$ at $k \, [h$ Mpc$^{-1}]\gtrsim 0.3$. On large scales ($k[h$ Mpc$^{-1}]\lesssim0.1$), the gain in accuracy resulting from cosmic-variance cancellation is $\sim$ 10$\%$ for the ratios of $P^{(0)}_α(k)$. We have carried out a Monte-Carlo Markov Chain analysis to determine the impact of these gains on several quantities derived from $P^{(0)}_α(k)$. If we push the measurement to scales $0.3 < k \, [h$ Mpc$^{-1}]< 0.5$, the average improvements are $\sim$ 30 $\%$ for the amplitudes of the monopoles, $\sim$ 70 $\%$ for the monopole ratios, and $\sim$ 20 $\%$ for the galaxy biases. Our results highlight the potential of MTOE to shed light upon the physics that operate both on large and small cosmological scales. The effect of MTOE on cosmological constraints using VIPERS data will be addressed in a separate paper.

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arXiv2016

Probing the sparse tails of redshift distributions with Voronoi tessellations

We introduce an algorithm to estimate the redshift distribution of a sample of galaxies selected photometrically given a subsample with measured spectroscopic redshifts. The approach uses a non-parametric Voronoi tessellation density estimator to interpolate the galaxy distribution in the redshift and photometric color space. We test the method on a mock dataset with a known color-redshift distribution. We find that the Voronoi tessellation estimator performs well at reconstructing the tails of the redshift distribution of individual galaxies and gives unbiased estimates of the first and second moments. The source code is publicly available at http://bitbucket.org/bengranett/tailz.

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arXiv2015

The Integrated Sachs-Wolfe Signal from BOSS Super-Structures

Cosmic structures leave an imprint on the microwave background radiation through the integrated Sachs-Wolfe effect. We construct a template map of the linear signal using the SDSS-III Baryon Acoustic Oscillation Survey at redshift 0.43 < z < 0.65. We verify the imprint of this map on the Planck CMB temperature map at the 97% confidence level and show consistency with the density-temperature cross-correlation measurement. Using this ISW reconstruction as a template we investigate the presence of ISW sources and further examine the properties of the Granett-Neyrinck-Szapudi supervoid and supercluster catalogue. We characterise the three-dimensional density profiles of these structures for the first time and demonstrate that they are significant structures. Model fits demonstrate that the supervoids are elongated along the line-of-sight and we suggest that this special orientation may be picked out by the void-finding algorithm in photometric redshift space. We measure the mean temperature profiles in Planck maps from public void and cluster catalogues. In an attempt to maximise the stacked ISW signal we construct a new catalogue of super-structures based upon local peaks and troughs of the gravitational potential. However, we do not find a significant correlation between these structures and the CMB temperature.

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arXiv2015

Detection of a Supervoid Aligned with the Cold Spot of the Cosmic Microwave Background

We use the WISE-2MASS infrared galaxy catalog matched with Pan-STARRS1 (PS1) galaxies to search for a supervoid in the direction of the Cosmic Microwave Background Cold Spot. Our imaging catalog has median redshift $z\simeq 0.14$, and we obtain photometric redshifts from PS1 optical colours to create a tomographic map of the galaxy distribution. The radial profile centred on the Cold Spot shows a large low density region, extending over 10's of degrees. Motivated by previous Cosmic Microwave Background results, we test for underdensities within two angular radii, $5^\circ$, and $15^\circ$. The counts in photometric redshift bins show significantly low densities at high detection significance, $\gtrsim 5 σ$ and $\gtrsim 6 σ$, respectively, for the two fiducial radii. The line-of-sight position of the deepest region of the void is $z\simeq 0.15-0.25$. Our data, combined with an earlier measurement by Granett et al. 2010, are consistent with a large $R_{\rm void}=(220 \pm 50) h^{-1}Mpc $ supervoid with $δ_{m} \simeq -0.14 \pm 0.04$ centered at $z=0.22\pm0.03$. Such a supervoid, constituting at least a $\simeq 3.3σ$ fluctuation in a Gaussian distribution of the $ΛCDM$ model, is a plausible cause for the Cold Spot.

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arXiv2014

Revisiting the screening mechanism in $f(R)$ gravity

We reexamine the screening mechanism in $f(R)$ gravity using N-body simulations. By explicitly examining the relation between the extra scalar field $δf_R$ and the gravitational potential $ϕ$ in the perturbed Universe, we find that the relation between these two fields plays an important role in understanding the screening mechanism. We show that the screening mechanism in $f(R)$ gravity depends mainly on the depth of the potential well, and find a useful condition for identifying unscreened halos in simulations. We also discuss the potential application of our results to real galaxy surveys.

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arXiv2014

Supervoid Origin of the Cold Spot in the Cosmic Microwave Background

We use a WISE-2MASS-Pan-STARRS1 galaxy catalog to search for a supervoid in the direction of the Cosmic Microwave Background Cold Spot. We obtain photometric redshifts using our multicolor data set to create a tomographic map of the galaxy distribution. The radial density profile centred on the Cold Spot shows a large low density region, extending over 10's of degrees. Motivated by previous Cosmic Microwave Background results, we test for underdensities within two angular radii, $5^\circ$, and $15^\circ$. Our data, combined with an earlier measurement by Granett et al 2010, are consistent with a large $R_{\rm void}=(192 \pm 15)h^{-1} Mpc $ $(2σ)$ supervoid with $δ\simeq -0.13 \pm 0.03$ centered at $z=0.22\pm0.01$. Such a supervoid, constituting a $\sim3.5 σ$ fluctuation in the $ΛCDM$ model, is a plausible cause for the Cold Spot.

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arXiv2014

The Cold Spot in the Cosmic Microwave Background: the Shadow of a Supervoid

Standard inflationary hot big bang cosmology predicts small fluctuations in the Cosmic Microwave Background (CMB) with isotropic Gaussian statistics. All measurements support the standard theory, except for a few anomalies discovered in the Wilkinson Microwave Anisotropy Probe maps and confirmed recently by the Planck satellite. The Cold Spot is one of the most significant of such anomalies, and the leading explanation of it posits a large void that imprints this extremely cold area via the linear Integrated Sachs-Wolfe (ISW) effect due to the decay of gravitational potentials over cosmic time, or via the Rees-Sciama (RS) effect due to late-time non-linear evolution. Despite several observational campaigns targeting the Cold Spot region, to date no suitably large void was found at higher redshifts $z > 0.3$. Here we report the detection of an $R =(192 \pm 15) h^{-1}Mpc$ size supervoid of depth $δ= -0.13 \pm 0.03$, and centred at redshift $z = 0.22$. This supervoid, possibly the largest ever found, is large enough to significantly affect the CMB via the non-linear RS effect, as shown in our Lemaitre-Tolman-Bondi framework. This discovery presents the first plausible explanation for any of the physical CMB anomalies, and raises the possibility that local large-scale structure could be responsible for other anomalies as well.

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arXiv2013

Cross-correlation of WMAP7 and the WISE Full Data Release

We measured the cross-correlation of the Wilkinson Microwave Anisotropy Probe (WMAP) 7 year temperature map and the full sky data release of the Wide-field Infrared Survey Explorer (WISE) galaxy map. Using careful mapmaking and masking techniques we find a positive cross-correlation signal. The results are fully consistent with a Lambda-CDM Universe, although not statistically significant. Our findings are robust against changing the galactic latitude cut from |b|>10 to |b|>20 and no color dependence was detected when we used WMAP Q, V or W maps. We confirm higher significance correlations found in the preliminary data release. The change in significance is consistent with cosmic variance.

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arXiv2012

Constraints on Massive Neutrinos from the CFHTLS Angular Power Spectrum

We use the galaxy angular power spectrum at $z\sim0.5-1.2$ from the Canada-France-Hawaii-Telescope Legacy Survey Wide fields (CFHTLS-Wide) to constrain separately the total neutrino mass $\sum{m_ν}$ and the effective number of neutrino species $N_{\rm{eff}}$. This survey has recently benefited from an accurate calibration of the redshift distribution, allowing new measurements of the (non-linear) matter power spectrum in a unique range of scales and redshifts sensitive to neutrino free streaming. Our analysis makes use of a recent model for the effect of neutrinos on the weakly non-linear matter power spectrum derived from accurate N-body simulations. We show that CFHTLS, combined with WMAP7 and a prior on the Hubble constant provides an upper limit of $\sum{m_ν}<0.29\,$eV and $N_{\rm{eff}} =4.17^{+1.62}_{-1.26}$ (2$\,σ$ confidence levels). If we omit smaller scales which may be affected by non-linearities, these constraints become $\sum{m_ν}<0.41\,$eV and $N_{\rm{eff}} =3.98^{+2.02}_{-1.20}$ (2$\,σ$ confidence levels). Finally we show that the addition of other large scale structures probes can further improve these constraints, demonstrating that high redshift large volumes surveys such as CFHTLS are complementary to other cosmological probes of the neutrino mass.

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arXiv2012

Cross-correlation of WISE Galaxies with the Cosmic Microwave Background

We estimated the cross-power spectra of a galaxy sample from the Wide-field Infrared Survey Explorer (WISE) survey with the 7-year Wilkinson Microwave Anisotropy Probe (WMAP) temperature anisotropy maps. A conservatively-selected galaxy sample covers ~13000sq.deg, with a median redshift of z=0.15. Cross-power spectra show correlations between the two data sets with no discernible dependence on the WMAP Q, V and W frequency bands. We interpret these results in terms of the the Integrated Sachs-Wolfe (ISW) effect: for the |b|>20 deg sample at l=6-87, we measure the amplitude (normalized to be 1 for vanilla LambdaCDM expectation) of the signal to be 3.4+-1.1, i.e., 3.1 sigma detection. We discuss other possibilities, but at face value, the detection of the linear ISW effect in a flat universe is caused by large scale decaying potentials, a sign of accelerated expansion driven by Dark Energy.

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arXiv2010

Galaxy Counts on the CMB Cold Spot

The Cold Spot on the Cosmic Microwave Background could arise due to a supervoid at low redshift through the integrated Sachs-Wolfe effect. We imaged the region with MegaCam on the Canada-France-Hawai'i Telescope and present galaxy counts in photometric redshift bins. We rule out the existence of a 100Mpc radius spherical supervoid with underdensity delta=-0.3 at 0.5<z<0.9 at high significance. The data are consistent with an underdensity at low redshift, but the fluctuations are within the range of cosmic variance and the low density areas are not contiguous on the sky. Thus, we find no strong evidence for a supervoid. We cannot resolve voids smaller than 50Mpc radius; however, these can only make a minor contribution to the CMB temperature decrement.

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arXiv2009

A Map of the Integrated Sachs-Wolfe Signal from Luminous Red Galaxies

We construct a map of the time derivative of the gravitational potential traced by SDSS Luminous Red Galaxies. The potential decays on large scales due to cosmic acceleration, leaving an imprint on cosmic microwave background (CMB) radiation through the integrated Sachs-Wolfe (ISW) effect. With a template fit, we directly measure this signature on the CMB at a 2-sigma confidence level. The measurement is consistent with the cross-correlation statistic, strengthening the claim that dark energy is indeed the cause of the correlation. This new approach potentially simplifies the cosmological interpretation. Our constructed linear ISW map shows no evidence for degree-scale cold and hot spots associated with supervoid and supercluster structures. This suggests that the linear ISW effect in a concordance Lambda-CDM cosmology is insufficient to explain the strong CMB imprints from these structures that we previously reported.

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arXiv2008

Dark Energy Detected with Supervoids and Superclusters

The observed apparent acceleration of the universe is usually attributed to negative pressure from a mysterious dark energy. This acceleration causes the gravitational potential to decay, heating or cooling photons travelling through crests or troughs of large-scale matter density fluctuations. This phenomenon, the late-time integrated Sachs-Wolfe (ISW) effect, has been detected, albeit at low significance, by cross-correlating various galaxy surveys with the Cosmic Microwave Background (CMB). Recently, the best evidence has come from the statistical combination of results from multiple correlated galaxy data sets. Here we show that vast structures identified in a galaxy survey project an image onto the CMB; stacking regions aligned with superclusters produces a hot spot, and supervoids, a cold spot. At over 4 sigma, this is the clearest evidence of the ISW effect to date. For the first time, our findings pin the effect to discrete structures. The ISW signal from supervoids and superclusters can be combined with other cosmological probes to constrain dark energy and cosmological parameters. In addition, our findings make it more plausible that the extreme Cold Spot and other anomalies in the CMB are caused by supervoids.

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