arXiv subjects

Federico Marulli

Publications and source records attributed to Federico Marulli.

At least 55 records · Page 3Linked to original sources

arXiv2017

Cosmological constraints from a joint analysis of cosmic growth and expansion

Combining measurements on the expansion history of the Universe and on the growth rate of cosmic structures is key to discriminate between alternative cosmological frameworks and to test gravity. Recently, Linder (2017) proposed a new diagram to investigate the joint evolutionary track of these two quantities. In this letter, we collect the most recent cosmic growth and expansion rate datasets to provide the state-of-the-art observational constraints on this diagram. By performing a joint statistical analysis of both probes, we test the standard $Λ$CDM model, confirming a mild tension between cosmic microwave background predictions from Planck mission and cosmic growth measurements at low redshift ($z<2$). Then we test alternative models allowing the variation of one single cosmological parameter at a time. In particular, we find a larger growth index than the one predicted by general relativity $γ=0.65^{+0.05}_{-0.04}$). However, also a standard model with total neutrino mass of $0.26\pm0.10$ eV provides a similarly accurate description of the current data. By simulating an additional dataset consistent with next-generation dark-energy mission forecasts, we show that growth rate constraints at $z>1$ will be crucial to discriminate between alternative models.

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arXiv2017

Redshift-space distortions of galaxies, clusters and AGN: testing how the accuracy of growth rate measurements depends on scales and sample selections

Redshift-space clustering anisotropies caused by cosmic peculiar velocities provide a powerful probe to test the gravity theory on large scales. However, to extract unbiased physical constraints, the clustering pattern has to be modelled accurately, taking into account the effects of non-linear dynamics at small scales, and properly describing the link between the selected cosmic tracers and the underlying dark matter field. We use a large hydrodynamic simulation to investigate how the systematic error on the linear growth rate, $f$, caused by model uncertainties, depends on sample selections and comoving scales. Specifically, we measure the redshift-space two-point correlation function of mock samples of galaxies, galaxy clusters and Active Galactic Nuclei, extracted from the Magneticum simulation, in the redshift range 0.2 < z < 2, and adopting different sample selections. We estimate $fσ_8$ by modelling both the monopole and the full two-dimensional anisotropic clustering, using the dispersion model. We find that the systematic error on $fσ_8$ depends significantly on the range of scales considered for the fit. If the latter is kept fixed, the error depends on both redshift and sample selection, due to the scale-dependent impact of non-linearities, if not properly modelled. On the other hand, we show that it is possible to get unbiased constraints on $fσ_8$ provided that the analysis is restricted to a proper range of scales, that depends non trivially on the properties of the sample. This can have a strong impact on multiple tracers analyses, and when combining catalogues selected at different redshifts.

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arXiv2017

Evolution of the real-space correlation function from next generation cluster surveys

We investigate to which accuracy it is possible to recover the real-space two-point correlation function of galaxy clusters from cluster catalogues based on photometric redshifts, and test our ability to measure the redshift and mass evolution of the correlation length and the bias parameter as a function of the redshift uncertainty. We calculate the correlation function for cluster sub-samples covering various mass and redshift bins selected from a light-cone catalogue. To simulate the distribution of clusters in photometric redshift space, we assign to each cluster a redshift randomly extracted from a Gaussian distribution. The dispersion is varied in the range $σ_{(z=0)} = 0.001$ to $0.050$. The correlation function in real-space is computed through estimation and deprojection of $w_{p}(r_{p})$. Four mass ranges (from $M_{halo}> 2 \times 10^{13}$ to $M_{halo}> 2 \times 10^{14}$) and six redshift slices covering the redshift range [0,2] are investigated, using cosmological redshifts and photo-z configurations. We find a clear increase of the correlation amplitude as a function of redshift and mass for the $z_{c}$ samples. The evolution of the derived bias parameter is in agreement with theoretical expectations. From our pilot sample limited to $M_{halo}> 5 \times 10^{13} (0.4 < z < 0.7)$, we find that the real-space correlation function can be recovered by deprojection of $w_{p}(r_{p})$ within an accuracy of 5% for $σ_{z} = 0.001 \times (1 + z_{c})$ and within 10% for $σ_{z} = 0.03 \times (1 + z_{c})$. The evolution of the correlation in redshift and mass is clearly detected for all $σ_{z}$ tested. The best-fit parameters $(r_{0}$ and $γ)$ as well as the bias obtained from the deprojection method for all $σ_{z}$ are within the $1 σ$ uncertainty of the $z_{c}$ sample.

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arXiv2016

Cosmology and Fundamental Physics with the Euclid Satellite

Euclid is a European Space Agency medium class mission selected for launch in 2020 within the Cosmic Vision 2015 2025 program. The main goal of Euclid is to understand the origin of the accelerated expansion of the universe. Euclid will explore the expansion history of the universe and the evolution of cosmic structures by measuring shapes and redshifts of galaxies as well as the distribution of clusters of galaxies over a large fraction of the sky. Although the main driver for Euclid is the nature of dark energy, Euclid science covers a vast range of topics, from cosmology to galaxy evolution to planetary research. In this review we focus on cosmology and fundamental physics, with a strong emphasis on science beyond the current standard models. We discuss five broad topics: dark energy and modified gravity, dark matter, initial conditions, basic assumptions and questions of methodology in the data analysis. This review has been planned and carried out within Euclid's Theory Working Group and is meant to provide a guide to the scientific themes that will underlie the activity of the group during the preparation of the Euclid mission.

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arXiv2016

CosmoBolognaLib: C++ libraries for cosmological calculations

We present the CosmoBolognaLib, a large set of Open Source C++ numerical libraries for cosmological calculations. CosmoBolognaLib is a living project aimed at defining a common numerical environment for cosmological investigations of the large-scale structure of the Universe. In particular, one of the primary focuses of this software is to help in handling astronomical catalogues, both real and simulated, measuring one-point, two-point and three-point statistics in configuration space, and performing cosmological analyses. In this paper, we discuss the main features of this software, providing an overview of all the available C++ classes implemented up to now. Both the CosmoBolognaLib and their associated doxygen documentation can be freely downloaded at https://github.com/federicomarulli/CosmoBolognaLib. We provide also some examples to explain how these libraries can be included in either C++ or Python codes.

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arXiv2015

Forecasts on neutrino mass constraints from the redshift-space two-point correlation function

We provide constraints on the accuracy with which the neutrino mass fraction, $f_ν$, can be estimated when exploiting measurements of redshift-space distortions, describing in particular how the error on neutrino mass depends on three fundamental parameters of a characteristic galaxy redshift survey: density, halo bias and volume. In doing this, we make use of a series of dark matter halo catalogues extracted from the BASICC simulation. The mock data are analysed via a Markov Chain Monte Carlo likelihood analysis. We find a fitting function that well describes the dependence of the error on bias, density and volume, showing a decrease in the error as the bias and volume increase, and a decrease with density down to an almost constant value for high density values. This fitting formula allows us to produce forecasts on the precision achievable with future surveys on measurements of the neutrino mass fraction. For example, a Euclid-like spectroscopic survey should be able to measure the neutrino mass fraction with an accuracy of $δf_ν \approx 6.7\times10^{-4}$, using redshift-space clustering once all the other cosmological parameters are kept fixed to the $Λ$CDM case.

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arXiv2015

Measuring the distance-redshift relation with the baryon acoustic oscillations of galaxy clusters

We analyse the largest spectroscopic samples of galaxy clusters to date, and provide observational constraints on the distance-redshift relation from baryon acoustic oscillations. The cluster samples considered in this work have been extracted from the Sloan Digital Sky Survey at three median redshifts, $z=0.2$, $z=0.3$, and $z=0.5$. The number of objects is $12910$, $42215$, and $11816$, respectively. We detect the peak of baryon acoustic oscillations for all the three samples. The derived distance constraints are: $r_s/D_V(z=0.2)=0.18 \pm 0.01$, $r_s/D_V(z=0.3)=0.124 \pm 0.004$ and $r_s/D_V(z=0.5)=0.080 \pm 0.002$. Combining these measurements, we obtain robust constraints on cosmological parameters. Our results are in agreement with the standard $Λ$ cold dark matter model. Specifically, we constrain the Hubble constant in a $Λ$CDM model, $H_0 = 64_{-9}^{+14} \, \mathrm{km} \, \mathrm{s}^{-1}\mathrm{Mpc}^{-1}$, the density of curvature energy, in the $oΛ$CDM context, $Ω_K = -0.015_{-0.36}^{+0.34}$, and finally the parameter of the dark energy equation of state in the $ow$CDM case, $w = -1.01_{-0.44}^{+0.44}$. This is the first time the distance-redshift relation has been constrained using only the peak of baryon acoustic oscillations of galaxy clusters.

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arXiv2015

Cosmology and fundamental physics with the Euclid satellite

Euclid is a European Space Agency medium class mission selected for launch in 2019 within the Cosmic Vision 2015-2025 programme. The main goal of Euclid is to understand the origin of the accelerated expansion of the Universe. Euclid will explore the expansion history of the Universe and the evolution of cosmic structures by measuring shapes and redshifts of galaxies as well as the distribution of clusters of galaxies over a large fraction of the sky. Although the main driver for Euclid is the nature of dark energy, Euclid science covers a vast range of topics, from cosmology to galaxy evolution to planetary research. In this review we focus on cosmology and fundamental physics, with a strong emphasis on science beyond the current standard models. We discuss five broad topics: dark energy and modified gravity, dark matter, initial conditions, basic assumptions and questions of methodology in the data analysis. This review has been planned and carried out within Euclid's Theory Working Group and is meant to provide a guide to the scientific themes that will underlie the activity of the group during the preparation of the Euclid mission.

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arXiv2015

Cosmic voids in coupled dark energy cosmologies: the impact of halo bias

In this work we analyse the properties of cosmic voids in standard and coupled dark energy cosmologies. Using large numerical simulations, we investigate the effects produced by the dark energy coupling on three statistics: the filling factor, the size distribution and the stacked profiles of cosmic voids. We find that the bias of the tracers of the density field used to identify the voids strongly influences the properties of the void catalogues, and, consequently, the possibility of using the identified voids as a probe to distinguish coupled dark energy models from the standard $Λ$CDM cosmology. In fact, on one hand coupled dark energy models are characterised by an excess of large voids in the cold dark matter distribution as compared to the reference standard cosmology, due to their higher normalisation of linear perturbations at low redshifts. Specifically, these models present an excess of large voids with $R_{eff}>20, 15, 12$ Mpc h^{-1}, at $z=0, 0.55, 1$, respectively. On the other hand, we do not find any significant difference in the properties of the void detected in the distribution of collapsed dark matter halos. These results imply that the tracer bias has a significant impact on the possibility of using cosmic void catalogues to probe cosmology.

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arXiv2015

New constraints on $σ_8$ from a joint analysis of stacked gravitational lensing and clustering of galaxy clusters

The joint analysis of clustering and stacked gravitational lensing of galaxy clusters in large surveys can constrain the formation and evolution of structures and the cosmological parameters. On scales outside a few virial radii, the halo bias, $b$, is linear and the lensing signal is dominated by the correlated distribution of matter around galaxy clusters. We discuss a method to measure the power spectrum amplitude $σ_8$ and $b$ based on a minimal modelling. We considered a sample of $\sim 120000$ clusters photometrically selected from the Sloan Digital Sky Survey in the redshift range $0.1<z<0.6$. The auto-correlation was studied through the two-point function of a subsample of $\sim 70000$ clusters; the matter-halo correlation was derived from the weak lensing signal of the subsample of $\sim 1200$ clusters with Canada-France-Hawaii Lensing Survey data. We obtained a direct measurement of $b$, which increases with mass in agreement with predictions of the $Λ$CDM paradigm. Assuming $Ω_\mathrm{M}=0.3$, we found $σ_8=0.78\pm0.16$. We used the same clusters for measuring both lensing and clustering and the estimate of $σ_8$ did require neither the mass-richness relation, nor the knowledge of the selection function, nor the modelling of $b$. With an additional theoretical prior on the bias, we obtained $σ_8=0.75\pm0.08$.

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arXiv2015

Cosmic voids detection without density measurements

Cosmic voids are effective cosmological probes to discriminate among competing world models. Their identification is generally based on density or geometry criteria that, because of their very nature, are prone to shot noise. We propose two void finders that are based on dynamical criterion to select voids in Lagrangian coordinates and minimise the impact of sparse sampling. The first approach exploits the Zel'dovich approximation to trace back in time the orbits of galaxies located in voids and their surroundings, the second uses the observed galaxy-galaxy correlation function to relax the objects' spatial distribution to homogeneity and isotropy. In both cases voids are defined as regions of the negative velocity divergence, that can be regarded as sinks of the back-in-time streamlines of the mass tracers. To assess the performance of our methods we used a dark matter halo mock catalogue CoDECS, and compared the results with those obtained with the ZOBOV void finder. We find that the void divergence profiles are less scattered than the density ones and, therefore, their stacking constitutes a more accurate cosmological probe. The significance of the divergence signal in the central part of voids obtained from both our finders is 60% higher than for overdensity profiles in the ZOBOV case. The ellipticity of the stacked void measured in the divergence field is closer to unity, as expected, than what is found when using halo positions. Therefore our void finders are complementary to the existing methods, that should contribute to improve the accuracy of void-based cosmological tests.

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arXiv2014

Disentangling interacting dark energy cosmologies with the three-point correlation function

We investigate the possibility of constraining coupled dark energy (cDE) cosmologies using the three-point correlation function (3PCF). Making use of the CoDECS N-body simulations, we study the statistical properties of cold dark matter (CDM) haloes for a variety of models, including a fiducial $Λ$CDM scenario and five models in which dark energy (DE) and CDM mutually interact. We measure both the halo 3PCF, $ζ(θ)$, and the reduced 3PCF, $Q(θ)$, at different scales ($2<r\,[$Mpc\h$]<40$) and redshifts ($0\leq z\leq2$). In all cDE models considered in this work, $Q(θ)$ appears flat at small scales (for all redshifts) and at low redshifts (for all scales), while it builds up the characteristic V-shape anisotropy at increasing redshifts and scales. With respect to the $Λ$CDM predictions, cDE models show lower (higher) values of the halo 3PCF for perpendicular (elongated) configurations. The effect is also scale-dependent, with differences between $Λ$CDM and cDE models that increase at large scales. We made use of these measurements to estimate the halo bias, that results in fair agreement with the one computed from the two-point correlation function (2PCF). The main advantage of using both the 2PCF and 3PCF is to break the bias$-σ_{8}$ degeneracy. Moreover, we find that our bias estimates are approximately independent of the assumed strength of DE coupling. This study demonstrates the power of a higher-order clustering analysis in discriminating between alternative cosmological scenarios, for both present and forthcoming galaxy surveys, such as e.g. BOSS and Euclid.

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arXiv2013

Cosmology with massive neutrinos I: towards a realistic modeling of the relation between matter, haloes and galaxies

By using a suite of large box-size N-body simulations that incorporate massive neutrinos as an extra set of particles, we investigate the impact of neutrino masses on the spatial distribution of dark matter haloes and galaxies. We compute the bias between the spatial distribution of dark matter haloes and the overall matter and cold dark matter distributions using statistical tools such as the power spectrum and the two-point correlation function. Overall we find a scale-dependent bias on large scales for the cosmologies with massive neutrinos. However, our results indicate that the scale-dependence in the bias is reduced if the latter is computed with respect to the cold dark matter distribution only. We find that the value of the bias on large scales is reasonably well reproduced by the Tinker fitting formula once the linear cold dark matter power spectrum is used, instead of the total matter power spectrum. We investigate whether scale-dependent bias really comes from purely neutrino's effect or from nonlinear gravitational collapse of haloes. For this purpose, we address the $Ω_ν$-$σ_8$ degeneracy and find that such degeneracy is not perfect, implying that neutrinos imprint a slight scale dependence on the large-scale bias. Finally, by using a simple halo occupation distribution (HOD) model, we investigate the impact of massive neutrinos on the distribution of galaxies within dark matter haloes. We use the main galaxy sample in the Sloan Digital Sky Survey II Data Release 7 to investigate if the small-scale galaxy clustering alone can be used to discriminate among different cosmological models with different neutrino masses. Our results suggest that different choices of the HOD parameters can reproduce the observational measurements relatively well, and we quantify the difference between the values of the HOD parameters between massless and massive neutrino cosmologies.

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arXiv2013

Characterizing dark interactions with the halo mass accretion history and structural properties

We study the halo mass accretion history (MAH) and its correlation with the internal structural properties in coupled dark energy cosmologies (cDE). To accurately predict all the non-linear effects caused by dark interactions, we use the COupled Dark Energy Cosmological Simulations (CoDECS). We measure the halo concentration at z=0 and the number of substructures above a mass resolution threshold for each halo. Tracing the halo merging history trees back in time, following the mass of the main halo, we develope a MAH model that accurately reproduces the halo growth in term of M_{200} in the ΛCDM Universe; we then compare the MAH in different cosmological scenarios. For cDE models with a weak constant coupling, our MAH model can reproduce the simulation results, within 10% of accuracy, by suitably rescaling the normalization of the linear matter power spectrum at z=0, σ_8. However, this is not the case for more complex scenarios, like the "bouncing" cDE model, for which the numerical analysis shows a rapid growth of haloes at high redshifts, that cannot be reproduced by simply rescaling the value of σ_8. Moreover, at fixed value of σ_8, cold dark matter (CDM) haloes in these cDE scenarios tend to be more concentrated and have a larger amount of substructures with respect to ΛCDM predictions. Finally, we present an accurate model that relates the halo concentration to the time at which it assembles half or 4% of its mass. Combining this with our MAH model, we show how halo concentrations change while varying only σ_8 in a ΛCDM Universe, at fixed halo mass.

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arXiv2013

Statistical and systematic errors in redshift-space distortion measurements from large surveys

We investigate the impact of statistical and systematic errors on measurements of linear redshift-space distortions (RSD) in future cosmological surveys, analyzing large catalogues of dark-matter halos from the BASICC simulation. These allow us to estimate the dependence of errors on typical survey properties, as volume, galaxy density and mass (i.e. bias factor) of the adopted tracer. We find that measures of the specific growth rate β=f/b using the Hamilton/Kaiser harmonic expansion of the redshift-space correlation function ξ(r_p,π) on scales larger than 3/h Mpc are typically under-estimated by up to 10% for galaxy sized halos. This is significantly larger than the corresponding statistical errors, which amount to a few percent, indicating the importance of non-linear improvements to the Kaiser model to obtain accurate measurements of the growth rate. We compare the statistical errors to predictions obtained with the Fisher information matrix, based on the usual FKP prescription for the errors on the power spectrum. We show that this produces parameter errors fairly similar to the standard deviations from the halo catalogues, but only if applied to strictly linear scales in Fourier space (k<0.2 h/Mpc). Finally, we present an accurate scaling formula describing the relative error on β as a function of the survey parameters, which closely matches the simulation results in all explored regimes. This provides a handy and plausibly more realistic alternative to the Fisher matrix approach, to quickly and accurately predict RSD statistical errors expected from future surveys.

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arXiv2012

Exploiting the shift of baryonic acoustic oscillations as a dynamical probe for dark interactions

The baryonic acoustic peak in the correlation function of galaxies and galaxy clusters provides a standard ruler to probe the space-time geometry of the Universe, jointly constraining the angular diameter distance and the Hubble expansion rate. Moreover, non-linear effects can systematically shift the peak position, giving us the opportunity to exploit this clustering feature also as a dynamical probe. We investigate the possibility of detecting interactions in the dark sector through an accurate determination of the baryonic acoustic scale. Making use of the public halo catalogues extracted from the CoDECS simulations -- the largest suite of N-body simulations of interacting dark energy models to date -- we determine the position of the baryonic scale fitting a band-filtered correlation function, specifically designed to amplify the signal at the sound horizon. We analyze the shifts due to non-linear dynamics, redshift-space distortions and Gaussian redshift errors, in the range 0 < z < 2. Since the coupling between dark energy and dark matter affects in a particular way the clustering properties of haloes and, specifically, the amplitude and location of the baryonic acoustic oscillations, the cosmic evolution of the baryonic peak position might provide a direct way to discriminate interacting dark energy models from the standard ΛCDM framework. To maximize the efficiency of the baryonic peak as a dynamic probe, the correlation function has to be measured in redshift-space, where the baryonic acoustic shift due to non-linearities is amplified. The typical redshift errors of spectroscopic galaxy surveys do not significantly impact these results.

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arXiv2012

Cosmology with clustering anisotropies: disentangling dynamic and geometric distortions in galaxy redshift surveys

We investigate the impact of different observational effects affecting a precise and accurate measurement of the growth rate of fluctuations from the anisotropy of clustering in galaxy redshift surveys. We focus on redshift measurement errors, on the reconstruction of the underlying real-space clustering and on the apparent degeneracy existing with the geometrical distortions induced by the cosmology-dependent conversion of redshifts into distances. We use a suite of mock catalogues extracted from large N-body simulations, focusing on the analysis of intermediate, mildly non-linear scales and apply the standard linear dispersion model to fit the anisotropy of the observed correlation function. We verify that redshift errors up to ~0.2% have a negligible impact on the precision with which the specific growth rate beta can be measured. Larger redshift errors introduce a positive systematic error, which can be alleviated by adopting a Gaussian distribution function of pairwise velocities. This is, in any case, smaller than the systematic error of up to 10% due to the limitations of the linear dispersion model, which is studied in a separate paper. We then show that 50% of the statistical error budget on beta depends on the deprojection procedure through which the real-space correlation function is obtained. Finally, we demonstrate that the degeneracy with geometric distortions can in fact be circumvented. This is obtained through a modified version of the Alcock-Paczynski test in redshift-space, which successfully recovers the correct cosmology by searching for the solution that optimizes the description of dynamical redshift distortions. For a flat cosmology, we obtain largely independent, robust constraints on beta and OmegaM. In a volume of 2.4(Gpc/h)^3, the correct OmegaM is obtained with ~12% error and negligible bias, once the real-space correlation function is properly reconstructed.

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arXiv2012

Size Evolution of Spheroids in a Hierarchical Universe

We present basic predictions of an updated version of the Munich semi-analytic hierarchical galaxy formation model that grows bulges via mergers and disk instabilities. Overall, we find that while spheroids below Ms ~ 10^11 Msun grow their sizes via a mixture of disk instability and mergers, galaxies above it mainly evolve via mergers. Including gas dissipation in major mergers, efficiently shrinks galaxies, especially those with final mass Ms < 10^11 Msun that are the most gas-rich, improving the match with different observables. We find that the predicted scatter in sizes at fixed stellar mass is still larger than the observed one by up to <40%. Spheroids are, on average, more compact at higher redshifts at fixed stellar mass, and at fixed redshift and stellar mass larger galaxies tend to be more starforming. More specifically, while for bulge-dominated galaxies the model envisages a nearly mass-independent decrease in sizes, the predicted size evolution for intermediate-mass galaxies is more complex. The z=2 progenitors of massive galaxies with mass around Ms and B/T>0.7 at z=0, are found to be mostly disc-dominated galaxies with a median B/T ~ 0.3, with only ~20% remaining bulge-dominated. The model also predicts that central spheroids living in more massive haloes tend to have larger sizes at fixed stellar mass. Including host halo mass dependence in computing velocity dispersions, allows the model to properly reproduce the correlations with stellar mass. We also discuss the fundamental plane, the correlations with galaxy age, the structural properties of pseudobulges, and the correlations with central black holes.

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