arXiv subjects

Federico Marulli

Publications and source records attributed to Federico Marulli.

62 records · Page 4Linked to original sources

arXiv2012

Clustering and redshift-space distortions in interacting dark energy cosmologies

We investigate the spatial properties of the large scale structure (LSS) of the Universe in the framework of coupled dark energy (cDE) cosmologies. Using the public halo catalogues from the CoDECS simulations -- the largest set of N-body experiments to date for such cosmological scenarios -- we estimate the clustering and bias functions of cold dark matter (CDM) haloes, both in real- and redshift-space. Moreover, we investigate the effects of the dark energy (DE) coupling on the geometric and dynamic redshift-space distortions, quantifying the difference with respect to the concordance LambdaCDM model. At z~0, the spatial properties of CDM haloes in cDE models appear very similar to the LambdaCDM case, even if the cDE models are normalized at last scattering in order to be consistent with the latest Cosmic Microwave Background (CMB) data. At higher redshifts, we find that the DE coupling produces a significant scale-dependent suppression of the halo clustering and bias function. This effect, that strongly depends on the coupling strength, is not degenerate with sigma8 at scales r<5-10 Mpc/h. Moreover, we find that the coupled DE strongly affects both the linear distortion parameter, beta, and the pairwise peculiar velocity dispersion, sigma12. Although the models considered in this work are found to be all in agreement with presently available observational data, the next generation of galaxy surveys will be able to put strong constraints on the level of coupling between DE and CDM exploiting the shape of redshift-space clustering anisotropies.

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arXiv2011

Effects of Massive Neutrinos on the Large-Scale Structure of the Universe

Cosmological neutrinos strongly affect the evolution of the largest structures in the Universe, i.e. galaxies and galaxy clusters. We use large box-size full hydrodynamic simulations to investigate the non-linear effects that massive neutrinos have on the spatial properties of cold dark matter (CDM) haloes. We quantify the difference with respect to the concordance LambdaCDM model of the halo mass function and of the halo two-point correlation function. We model the redshift-space distortions and compute the errors on the linear distortion parameter beta introduced if cosmological neutrinos are assumed to be massless. We find that, if not taken correctly into account and depending on the total neutrino mass, these effects could lead to a potentially fake signature of modified gravity. Future nearly all-sky spectroscopic galaxy surveys will be able to constrain the neutrino mass if it is larger than 0.6 eV, using beta measurements alone and independently of the value of the matter power spectrum normalisation. In combination with other cosmological probes, this will strengthen neutrino mass constraints and help breaking parameter degeneracies.

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arXiv2011

Expected properties of the Two-Point Autocorrelation Function of the IGM

Recent analyses of the fluctuations of the soft Diffuse X-ray Background (DXB) have provided indirect detection of a component consistent with the elusive Warm Hot Intergalactic Medium (WHIM). In this work we use theoretical predictions obtained from hydrodynamical simulations to investigate the angular correlation properties of the WHIM in emission and assess the possibility of indirect detection with next-generation X-ray missions. Our results indicate that the angular correlation signal of the WHIM is generally weak but dominates the angular correlation function of the DXB outside virialized regions. Its indirect detection is possible but requires rather long exposure times [0.1-1] Ms, large (~1° x1°) fields of view and accurate subtraction of isotropic fore/background contributions, mostly contributed by Galactic emission. The angular correlation function of the WHIM is positive for θ < 5' and provides limited information on its spatial distribution. A satisfactory characterization of the WHIM in 3D can be obtained through spatially resolved spectroscopy. 1 Ms long exposures with next generation detectors will allow to detect ~400 O VII+O VIII X-ray emission systems that we use to trace the spatial distribution of the WHIM. We predict that these observations will allow to estimate the WHIM correlation function with high statistical significance out to ~10 Mpc h^-1 and characterize its dynamical state through the analysis of redshift-space distortions. The detectable WHIM, which is typically associated with the outskirts of virialized regions rather than the filaments has a non-zero correlation function with slope γ = -1.7 \pm 0.1 and correlation length r0 = 4.0 \pm 0.1 Mpc h^-1 in the range r = [4.5, 12] Mpc h^-1. Redshift space distances can be measured to assess the dynamical properties of the gas, typically infalling onto large virialized structures.

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arXiv2010

Further constraining galaxy evolution models through the Size Function of SDSS Early-type galaxies

We discuss how the effective radius Phi(Re) function (ERF) recently worked out by Bernardi et al. (2009) represents a new testbed to improve the current understanding of Semi-analytic Models of Galaxy formation. In particular, we here show that a detailed hierarchical model of structure formation can broadly reproduce the correct peak in the size distribution of local early-type galaxies, although it significantly overpredicts the number of very compact and very large galaxies. This in turn is reflected in the predicted size-mass relation, much flatter than the observed one, due to too large (~3 kpc) low-mass galaxies (<10^11 \msun), and to a non-negligible fraction of compact (< 0.5-1 kpc) and massive galaxies (> 10^11 \msun). We also find that the latter discrepancy is smaller than previously claimed, and limited to only ultracompact (Re < 0.5 kpc) galaxies when considering elliptical-dominated samples. We explore several causes behind these effects. We conclude that the former problem might be linked to the initial conditions, given that large and low-mass galaxies are present at all epochs in the model. The survival of compact and massive galaxies might instead be linked to their very old ages and peculiar merger histories. Overall, knowledge of the galactic stellar mass {\em and} size distributions allows a better understanding of where and how to improve models.

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arXiv2009

Sizes and ages of SDSS ellipticals: Comparison with hierarchical galaxy formation models

In a sample of about 45,700 early-type galaxies extracted from SDSS, we find that the shape, normalization, and dispersion around the mean size-stellar mass relation is the same for young and old systems, provided the stellar mass is greater than 3*10^10 Msun. This is difficult to reproduce in pure passive evolution models, which generically predict older galaxies to be much more compact than younger ones of the same stellar mass. However, this aspect of our measurements is well reproduced by hierarchical models of galaxy formation. Whereas the models predict more compact galaxies at high redshifts, subsequent minor, dry mergers increase the sizes of the more massive objects, resulting in a flat size-age relation at the present time. At lower masses, the models predict that mergers are less frequent, so that the expected anti-correlation between age and size is not completely erased. This is in good agreement with our data: below 3*10^10 Msun, the effective radius R_e is a factor of ~2 lower for older galaxies. These successes of the models are offset by the fact that the predicted sizes have other serious problems, which we discuss.

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arXiv2009

Modeling the cosmological co-evolution of supermassive black holes and galaxies: II. The clustering of quasars and their dark environment

We use semi-analytic modeling on top of the Millennium simulation to study the joint formation of galaxies and their embedded supermassive black holes. Our goal is to test scenarios in which black hole accretion and quasar activity are triggered by galaxy mergers, and to constrain different models for the lightcurves associated with individual quasar events. In the present work we focus on studying the spatial distribution of simulated quasars. At all luminosities, we find that the simulated quasar two-point correlation function is fit well by a single power-law in the range 0.5 < r < 20 h^{-1} Mpc, but its normalization is a strong function of redshift. When we select only quasars with luminosities within the range typically accessible by today's quasar surveys, their clustering strength depends only weakly on luminosity, in agreement with observations. This holds independently of the assumed lightcurve model, since bright quasars are black holes accreting close to the Eddington limit, and are hosted by dark matter haloes with a narrow mass range of a few 10^12 h^{-1} M_sun. Therefore the clustering of bright quasars cannot be used to disentangle lightcurve models, but such a discrimination would become possible if the observational samples can be pushed to significantly fainter limits. Overall, our clustering results for the simulated quasar population agree rather well with observations, lending support to the conjecture that galaxy mergers could be the main physical process responsible for triggering black hole accretion and quasar activity.

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arXiv2009

The spatial distribution of X-ray selected AGN in the Chandra deep fields: a theoretical perspective

We study the spatial distribution of X-ray selected AGN in the framework of hierarchical co-evolution of supermassive black holes and their host galaxies and dark matter haloes. To this end, we have applied the model developed by Croton et al.(2006), De Lucia & Blaizot(2007) and Marulli et al.(2008) to the output of the Millennium Run and obtained hundreds of realizations of past light-cones from which we have extracted realistic mock AGN catalogues that mimic the Chandra deep fields. We find that the model AGN number counts are in fair agreement with observations, except at fluxes <1e-15 erg/cm^2/s. The spatial two-point correlation function predicted by the model is well described by a power-law relation out to 20 Mpc/h, in close agreement with observations. Our model matches the correlation length r_0 of AGN in the Chandra Deep Field North but underestimates it in the Chandra Deep Field South. When fixing the slope to gamma = 1.4, as in Gilli et al. (2005), the statistical significance of the mismatch is 2-2.5 sigma, suggesting that the predicted cosmic variance, which dominates the error budget, may not account for the different correlation length of the AGN in the two fields. While our results are robust to changes in the model prescriptions for the AGN lightcurves, the luminosity dependence of the clustering is sensitive to the different lightcurve models adopted. However, irrespective of the model considered, the luminosity dependence of the AGN clustering in our mock fields seems to be weaker than in the real Chandra fields. The significance of this mismatch needs to be confirmed using larger datasets.

astro-ph.CO↗

arXiv2007

Modeling the cosmological co-evolution of supermassive black holes and galaxies: I. BH scaling relations and the AGN luminosity function

We model the cosmological co-evolution of galaxies and their central supermassive black holes (BHs) within a semi-analytical framework developed on the outputs of the Millennium Simulation. This model, described in detail in Croton et al. (2006) and De Lucia & Blaizot (2007), introduces a `radio mode' feedback from Active Galactic Nuclei (AGN) at the centre of X-ray emitting atmospheres in galaxy groups and clusters. Thanks to this mechanism, the model can simultaneously explain: (i) the low observed mass drop-out rate in cooling flows; (ii) the exponential cut-off in the bright end of the galaxy luminosity function; and (iii) the bulge-dominated morphologies and old stellar ages of the most massive galaxies in clusters. This paper is the first of a series in which we investigate how well this model can also reproduce the physical properties of BHs and AGN. Here we analyze the scaling relations, the fundamental plane and the mass function of BHs, and compare them with the most recent observational data. Moreover, we extend the semi-analytic model to follow the evolution of the BH mass accretion and its conversion into radiation, and compare the derived AGN bolometric luminosity function with the observed one. While we find for the most part a very good agreement between predicted and observed BH properties, the semi-analytic model underestimates the number density of luminous AGN at high redshifts, independently of the adopted Eddington factor and accretion efficiency. However, an agreement with the observations is possible within the framework of our model, provided it is assumed that the cold gas fraction accreted by BHs at high redshifts is larger than at low redshifts.

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