arXiv subjects

Elena Rasia

Publications and source records attributed to Elena Rasia.

At least 55 records · Page 3Linked to original sources

arXiv2021

Galaxy Velocity Bias in Cosmological Simulations: Towards Percent-level Calibration

Galaxy cluster masses, rich with cosmological information, can be estimated from internal dark matter (DM) velocity dispersions, which in turn can be observationally inferred from satellite galaxy velocities. However, galaxies are biased tracers of the DM, and the bias can vary over host halo and galaxy properties as well as time. We precisely calibrate the velocity bias, b_v -- defined as the ratio of galaxy and DM velocity dispersions -- as a function of redshift, host halo mass, and galaxy stellar mass threshold (Mstarsat), for massive halos (M200c > 1e13.5 msun) from five cosmological simulations: IllustrisTNG, Magneticum, Bahamas + Macsis, The Three Hundred Project, and MultiDark Planck-2. We first compare scaling relations for galaxy and DM velocity dispersion across simulations; the former is estimated using a new ensemble velocity likelihood method that is unbiased for low galaxy counts per halo, while the latter uses a local linear regression. The simulations show consistent trends of b_v increasing with M200c and decreasing with redshift and Mstarsat. The ensemble-estimated theoretical uncertainty in b_v is 2-3% but becomes percent-level when considering only the three highest resolution simulations. We update the mass-richness normalization previously estimated by Farahi et al. (2016) for an SDSS redMaPPer cluster sample. The improved accuracy of our b_v estimates reduces the mass normalization uncertainty from 22% to 8%, demonstrating that dynamical estimation techniques can be competitive with weak lensing in calibrating population mean masses. We discuss necessary steps for further improving this precision. Our estimates for b_v(M200c, Mstarsat, z) are made publicly available.

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arXiv2021

The hydrostatic mass bias in The Three Hundred clusters

Hydrostatic equilibrium (HE) is often used in observations to estimate galaxy clusters masses. We use a set of almost 300 simulated clusters from The Three Hundred Project, to estimate the cluster HE mass and the bias deriving from it. We study the dependence of the bias on several dynamical state indicators across a redshift range from 0.07 to 1.3, finding no dependence between them. Moreover, we focus our attention on the evolution of the HE bias during the merger phase, where the bias even reaches negative values due to an overestimation of the mass with HE.

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arXiv2021

Morphological analysis of SZ and X-ray maps of galaxy clusters with Zernike polynomials

Several methods are used to evaluate, from observational data, the dynamical state of galaxy clusters. Among them, the morphological analysis of cluster images is well suited for this purpose. We report a new approach to the morphology, which consists in analytically modelling the images with a set of orthogonal functions, the Zernike polynomials (ZPs). We validated the method on mock high-resolution Compton parameter maps of synthetic galaxy clusters from THE THREE HUNDRED project. To classify the maps for their morphology we defined a single parameter, $\mathcal{C}$, by combining the contribution of some ZPs in the modelling. We verify that $\mathcal{C}$ is linearly correlated with a combination of common morphological parameters and also with a proper 3D dynamical-state indicator available for the synthetic clusters we used. We also show the early results of the Zernike modelling applied on Compton parameter maps of local clusters ($z < 0.1$) observed by the $\textit{Planck}$ satellite. At last, we report the preliminary results of this kind of morphological analysis on mock X-ray maps of THE THREE HUNDRED clusters.

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arXiv2021

Exploring the role of cosmological shock waves in the Dianoga simulations of galaxy clusters

Cosmological shock waves are ubiquitous to cosmic structure formation and evolution. As a consequence, they play a major role in the energy distribution and thermalization of the intergalactic medium (IGM). We analyze the Mach number distribution in the Dianoga simulations of galaxy clusters performed with the SPH code GADGET-3. The simulations include the effects of radiative cooling, star formation, metal enrichment, supernova and active galactic nuclei feedback. A grid-based shock-finding algorithm is applied in post-processing to the outputs of the simulations. This procedure allows us to explore in detail the distribution of shocked cells and their strengths as a function of cluster mass, redshift and baryonic physics. We also pay special attention to the connection between shock waves and the cool-core/non-cool core (CC/NCC) state and the global dynamical status of the simulated clusters. In terms of general shock statistics, we obtain a broad agreement with previous works, with weak (low-Mach number) shocks filling most of the volume and processing most of the total thermal energy flux. As a function of cluster mass, we find that massive clusters seem more efficient in thermalising the IGM and tend to show larger external accretion shocks than less massive systems. We do not find any relevant difference between CC and NCC clusters. However, we find a mild dependence of the radial distribution of the shock Mach number on the cluster dynamical state, with disturbed systems showing stronger shocks than regular ones throughout the cluster volume.

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arXiv2021

The Lack of Non-Thermal Motions in Galaxy Cluster Cores

We report the non-thermal pressure fraction (Pnt/Ptot) obtained from a three-dimensional triaxial analysis of 16 galaxy clusters in the CLASH sample using gravitational lensing (GL) data primarily from Subaru and HST, X-ray spectroscopic imaging from Chandra, and Sunyaev-Zel'dovich effect (SZE) data from Planck and Bolocam. Our results span the approximate radial range 0.015-0.4R200m (35-1000 kpc). At cluster-centric radii smaller than 0.1R200m the ensemble average Pnt/Ptot is consistent with zero with an upper limit of nine per cent, indicating that heating from active galactic nuclei and other relevant processes does not produce significant deviations from hydrostatic equilibrium (HSE). The ensemble average Pnt/Ptot increases outside of this radius to approximately 20 per cent at 0.4R200m, as expected from simulations, due to newly accreted material thermalizing via a series of shocks. Also in agreement with simulations, we find significant cluster-to-cluster variation in Pnt/Ptot and little difference in the ensemble average Pnt/Ptot based on dynamical state. We conclude that on average, even for diverse samples, HSE-derived masses in the very central regions of galaxy clusters require only modest corrections due to non-thermal motions.

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arXiv2021

The Three Hundred Project: Dynamical state of galaxy clusters and morphology from multi-wavelength synthetic maps

We study the connection between morphology and dynamical state of the simulated galaxy clusters in $z\in[0,1.031]$ from THE THREE HUNDRED Project. We quantify cluster dynamical state using a combination of dynamical indicators from theoretical measures and compare this combined parameter, $χ$, with the results from morphological classifications. The dynamical state of the cluster sample shows a continuous distribution from dynamically relaxed, more abundant at lower redshift, to hybrid and disturbed. The dynamical state presents a clear dependence on the radius, with internal regions more relaxed than outskirts. The morphology from multi-wavelength mock observation of clusters in X-ray, optical, and Sunyaev-Zel'dovich (SZ) effect images, is quantified by $M$ -- a combination of six parameters for X-ray and SZ maps and the offsets between the optical position of the Brightest Central Galaxy (BCG) and the X-ray/SZ centroids. All the morphological parameters are highly correlated with each other, while they show a moderately strong correlation with the dynamical $χ$ parameter. The X-ray or SZ peaks are less affected by the dynamical state than centroids, which results in reliable tracers of the cluster density peak. The principal source of contamination in the relaxed cluster fraction, inferred from morphological parameters, is due to dynamically hybrid clusters. Compared to individual parameters, which consider only one aspect of cluster property (e.g. only clumping or asymmetry), the combined morphological and dynamical parameters ($M$ and $χ$) collect more information and provide a single and more accurate estimation of the cluster dynamical state.

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arXiv2021

Cosmic filaments in galaxy cluster outskirts: quantifying finding filaments in redshift space

Inferring line-of-sight distances from redshifts in and around galaxy clusters is complicated by peculiar velocities, a phenomenon known as the "Fingers of God" (FoG). This presents a significant challenge for finding filaments in large observational data sets as these artificial elongations can be wrongly identified as cosmic web filaments by extraction algorithms. Upcoming targeted wide-field spectroscopic surveys of galaxy clusters and their infall regions such as the WEAVE Wide-Field Cluster Survey motivate our investigation of the impact of FoG on finding filaments connected to clusters. Using zoom-in resimulations of 324 massive galaxy clusters and their outskirts from The ThreeHundred project, we test methods typically applied to large-scale spectroscopic data sets. This paper describes our investigation of whether a statistical compression of the FoG of cluster centres and galaxy groups can lead to correct filament extractions in the cluster outskirts. We find that within 5 R200 (~15 Mpc/h) statistically correcting for FoG elongations of virialized regions does not achieve reliable filament networks compared to reference filament networks based on true positions. This is due to the complex flowing motions of galaxies towards filaments in addition to the cluster infall, which overwhelm the signal of the filaments relative to the volume we probe. While information from spectroscopic redshifts is still important to isolate the cluster regions, and thereby reduce background and foreground interlopers, we expect future spectroscopic surveys of galaxy cluster outskirts to rely on 2D positions of galaxies to extract cosmic filaments.

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arXiv2021

Exploring the hydrostatic mass bias in MUSIC clusters: application to the NIKA2 mock sample

Clusters of galaxies are useful tools to constrain cosmological parameters, only if their masses can be correctly inferred from observations. In particular, X-ray and Sunyaev-Zeldovich (SZ) effect observations can be used to derive masses within the framework of the hydrostatic equilibrium. Therefore, it is crucial to have a good control of the possible mass biases that can be introduced when this hypothesis is not valid. In this work, we analyzed a set of 260 synthetic clusters from the MUSIC simulation project, at redshifts $0 \leq z \leq 0.82$. We estimate the hydrostatic mass of the MUSIC clusters from X-ray only (temperature and density) and from X-ray and SZ (density and pressure). Then, we compare them with the true 3D dynamical mass. The biases are of the order of 20%. We find that using the temperature instead of the pressure leads to a smaller bias, although the two values are compatible within 1$σ$. Non-thermal contributions to the total pressure support, arising from bulk motion and turbulence of the gas, are also computed and show that they are sufficient to account for this bias. We also present a study of the correlation between the mass bias and the dynamical state of the clusters. A clear correlation is shown between the relaxation state of the clusters and the bias factor. We applied the same analysis on a subsample of 32 objects, already selected for supporting the NIKA2 SZ Large Program.

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arXiv2020

The Three Hundred Project: quest of clusters of galaxies morphology and dynamical state through Zernike Polynomials

The knowledge of the dynamical state of galaxy clusters allows to alleviate systematics when observational data from these objects are applied in cosmological studies. Evidence of correlation between the state and the morphology of the clusters is well studied. The morphology can be inferred by images of the surface brightness in the X-ray band and of the thermal component of the Sunyaev-Zel'dovich (tSZ) effect in the millimetre range. For this purpose, we apply, for the first time, the Zernike polynomial decomposition, a common analytic approach mostly used in adaptive optics to recover aberrated radiation wavefronts at the telescopes pupil plane. With this novel way we expect to correctly infer the morphology of clusters and so possibly, their dynamical state. To verify the reliability of this new approach we use more than 300 synthetic clusters selected in THE THREE HUNDRED project at different redshifts ranging from 0 up to 1.03. Mock maps of the tSZ, quantified with the Compton parameter, $y$-maps, are modelled with Zernike polynomials inside $R_{500}$, the cluster reference radius. We verify that it is possible to discriminate the morphology of each cluster by estimating the contribution of the different polynomials to the fit of the map. The results of this new method are correlated with those of a previous analysis made on the same catalogue, using two parameters that combine either morphological or dynamical-state probes. We underline that instrumental angular resolution of the maps has an impact mainly when we extend this approach to high-redshift clusters.

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arXiv2020

The ThreeHundred: the structure and properties of cosmic filaments in the outskirts of galaxy clusters

Galaxy cluster outskirts are described by complex velocity fields induced by diffuse material collapsing towards filaments, gas and galaxies falling into clusters, and gas shock processes triggered by substructures. A simple scenario that describes the large-scale tidal fields of the cosmic web is not able to fully account for this variety, nor for the differences between gas and collisionless dark matter. We have studied the filamentary structure in zoom-in resimulations centred on 324 clusters from The ThreeHundred project, focusing on differences between dark and baryonic matter. This paper describes the properties of filaments around clusters out to five $R_{200}$, based on the diffuse filament medium where haloes had been removed. For this, we stack the remaining particles of all simulated volumes to calculate the average profiles of dark matter and gas filaments. We find that filaments increase their thickness closer to nodes and detect signatures of gas turbulence at a distance of $\sim 2 h^{-1}\rm{Mpc}$ from the cluster. These are absent in dark matter. Both gas and dark matter collapse towards filament spines at a rate of $\sim 200 h^{-1} \rm{km ~ s^{-1}} $. We see that gas preferentially enters the cluster as part of filaments, and leaves the cluster centre outside filaments. We further see evidence for an accretion shock just outside the cluster. For dark matter, this preference is less obvious. We argue that this difference is related to the turbulent environment. This indicates that filaments act as highways to fuel the inner regions of clusters with gas and galaxies.

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arXiv2020

Brightest Cluster Galaxies: the centre can(not?) hold

We explore the persistence of the alignment of brightest cluster galaxies (BCGs) with their local environment. We find that a significant fraction of BCGs do not coincide with the centroid of the X-ray gas distribution and/or show peculiar velocities (they are not at rest with respect to the cluster mean). Despite this, we find that BCGs are generally aligned with the cluster mass distribution even when they have significant offsets from the X-ray centre and significant peculiar velocities. The large offsets are not consistent with simple theoretical models. To account for these observations BCGs must undergo mergers preferentially along their major axis, the main infall direction. Such BCGs may be oscillating within the cluster potential after having been displaced by mergers or collisions, or the dark matter halo itself may not yet be relaxed.

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arXiv2020

An excess of small-scale gravitational lenses observed in galaxy clusters

Cold dark matter (CDM) constitutes most of the matter in the Universe. The interplay between dark and luminous matter in dense cosmic environments like galaxy clusters is studied theoretically using cosmological simulations. Observed gravitational lensing is used to test and characterize the properties of substructures - the small-scale distribution of dark matter - in clusters. An apt metric, the probability of strong lensing events produced by dark matter substructure, is devised and computed for 11 galaxy clusters. We report that observed cluster substructures are more efficient lenses than predicted by CDM simulations, by more than an order of magnitude. We suggest that hitherto undiagnosed systematic issues with simulations or incorrect assumptions about the properties of dark matter could explain our results.

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arXiv2020

Iron in X-COP: tracing enrichment in cluster outskirts with high accuracy abundance profiles

We present the first metal abundance profiles for a representative sample of massive clusters. Our measures extend to $R_{500}$ and are corrected for a systematic error plaguing previous outskirt estimates. Our profiles flatten out at large radii, admittedly not a new result, however the radial range and representative nature of our sample extends its import well beyond previous findings. We find no evidence of segregation between cool-core and non-cool-core systems beyond $\sim 0.3 R_{500}$, implying that, as was found for thermodynamic properties (Ghirardini et al, 2019), the physical state of the core does not affect global cluster properties. Our mean abundance within $R_{500}$ shows a very modest scatter, $< $15%, suggesting the enrichment process must be quite similar in all these massive systems. This is a new finding and has significant implications on feedback processes. Together with results from thermodynamic properties presented in a previous X-COP paper, it affords a coherent picture where feedback effects do not vary significantly from one system to another. By combing ICM with stellar measurements we have found the amount of Fe diffused in the ICM to be about ten times higher than that locked in stars. Although our estimates suggest, with some strength, that the measured iron mass in clusters is well in excess of the predicted one, systematic errors prevent us from making a definitive statement. Further advancements will only be possible when systematic uncertainties, principally those associated to stellar masses, both within and beyond $R_{500}$, can be reduced.

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arXiv2020

Evolution and Role of Mergers in the BCG-Cluster Alignment. A View from Cosmological Hydro-Simulations

Contradictory results have been reported on the time evolution of the alignment between clusters and their Brightest Cluster Galaxy (BCG). We study this topic by analyzing cosmological hydro-simulations of 24 massive clusters with $M_{200}|_{z=0} \gtrsim 10^{15}\, M_\odot$, plus 5 less massive with $1 \times 10^{14} \lesssim M_{200}|_{z=0} \lesssim 7 \times 10^{14}\, M_\odot$, which have already proven to produce realistic BCG masses. We compute the BCG alignment with both the distribution of cluster galaxies and the dark matter (DM) halo. At redshift $z=0$, the major axes of the simulated BCGs and their host cluster galaxy distributions are aligned on average within 20$^\circ$. The BCG alignment with the DM halo is even tighter. The alignment persists up to $z\lesssim2$ with no evident evolution. This result continues, although with a weaker signal, when considering the projected alignment. The cluster alignment with the surrounding distribution of matter ($3R_{200}$) is already in place at $z\sim4$ with a typical angle of $35^\circ$, before the BCG-Cluster alignment develops. The BCG turns out to be also aligned with the same matter distribution, albeit always to a lesser extent. These results taken together might imply that the BCG-Cluster alignment occurs in an outside-in fashion. Depending on their frequency and geometry, mergers can promote, destroy or weaken the alignments. Clusters that do not experience recent major mergers are typically more relaxed and aligned with their BCG. In turn, accretions closer to the cluster elongation axis tend to improve the alignment as opposed to accretions closer to the cluster minor axis.

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arXiv2020

The Three Hundred Project: the stellar and gas profiles

Using the catalogues of galaxy clusters from The Three Hundred project, modelled with both hydrodynamic simulations, (Gadget-X and Gadget-MUSIC), and semi-analytic models (SAMs), we study the scatter and self-similarity of the profiles and distributions of the baryonic components of the clusters: the stellar and gas mass, metallicity, the stellar age, gas temperature, and the (specific) star formation rate. Through comparisons with observational results, we find that the shape and the scatter of the gas density profiles matches well the observed trends including the reduced scatter at large radii which is a signature of self-similarity suggested in previous studies. One of our simulated sets, Gadget-X, reproduces well the shape of the observed temperature profile, while Gadget-MUSIC has a higher and flatter profile in the cluster centre and a lower and steeper profile at large radii. The gas metallicity profiles from both simulation sets, despite following the observed trend, have a relatively lower normalisation. The cumulative stellar density profiles from SAMs are in better agreement with the observed result than both hydrodynamic simulations which show relatively higher profiles. The scatter in these physical profiles, especially in the cluster centre region, shows a dependence on the cluster dynamical state and on the cool-core/non-cool-core dichotomy. The stellar age, metallicity and (s)SFR show very large scatter, which are then presented in 2D maps. We also do not find any clear radial dependence of these properties. However, the brightest central galaxies have distinguishable features compared to the properties of the satellite galaxies.

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arXiv2019

Black hole mass of central galaxies and cluster mass correlation in cosmological hydro-dynamical simulations

Recently, relations connecting the SMBH mass of central galaxies and global properties of the hosting cluster, such as temperature and mass, were observed. We investigate the correlation between SMBH mass and cluster mass and temperature, their establishment and evolution. We compare their scatter to that of the classical $M_{\rm BH}-M_{\rm BCG}$ relation. We study how gas accretion and BH-BH mergers contribute to SMBH growth across cosmic time. We employed 135 groups and clusters with a mass range $1.4\times 10^{13}M_{\odot}-2.5\times 10^{15} M_{\odot}$ extracted from a set of 29 zoom-in cosmological hydro-dynamical simulations where the baryonic physics is treated with various sub-grid models, including feedback by AGN. In our simulations we find that $M_{\rm BH}$ correlates well with $M_{500}$ and $T_{500}$, with the scatter around these relations compatible within $2σ$ with the scatter around $M_{\rm BH}-M_{\rm BCG}$ at $z=0$. The $M_{\rm BH}-M_{500}$ relation evolves with time, becoming shallower at lower redshift as a direct consequence of hierarchical structure formation. On average, in our simulations the contribution of gas accretion to the total SMBH mass dominates for the majority of the cosmic time ($z>0.4$), while in the last 2 Gyr the BH-BH mergers become a larger contributor. During this last process, substructures hosting SMBHs are disrupted in the merger process with the BCG and the unbound stars enrich the diffuse stellar component rather than increase BCG mass. From the results obtained in our simulations with simple sub-grid models we conclude that the scatter around the $M_{\rm BH}-T_{500}$ relation is comparable to the scatter around the $M_{\rm BH}-M_{\rm BCG}$ relation and that, given the observational difficulties related to the estimation of the BCG mass, clusters temperature and mass can be a useful proxy for the SMBHs mass, especially at high redshift.

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arXiv2019

Deriving the Hubble constant using Planck and XMM-Newton observations of galaxy clusters

The possibility of determining the value of the Hubble constant using observations of galaxy clusters in X-ray and microwave wavelengths through the Sunyaev Zeldovich (SZ) effect has long been known. Previous measurements have been plagued by relatively large errors in the observational data and severe biases induced, for example, by cluster triaxiality and clumpiness. The advent of \textit{Planck} allows us to map the Compton parameter y, that is, the amplitude of the SZ effect, with unprecedented accuracy at intermediate cluster-centric radii, which in turn allows performing a detailed spatially resolved comparison with X-ray measurements. Given such higher quality observational data, we developed a Bayesian approach that combines informed priors on the physics of the intracluster medium obtained from hydrodynamical simulations of massive clusters with measurement uncertainties. We apply our method to a sample of 61 galaxy clusters with redshifts up to z < 0.5 observed with Planck and XMM-Newton observations and find H_0=67 \pm 3 km s^{-1} Mpc^{-1}.

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arXiv2019

The Three Hundred Project: Ram pressure and gas content of haloes and subhaloes in the phase-space plane

We use TheThreeHundred project, a suite of 324 resimulated massive galaxy clusters embedded in a broad range of environments, to investigate (i) how the gas content of surrounding haloes correlates with phase-space position at $z=0$, and (ii) to investigate the role that ram pressure plays in this correlation. By stacking all 324 normalised phase-space planes containing 169287 haloes and subhaloes, we show that the halo gas content is tightly correlated with phase-space position. At $\sim\,1.5-2\,\text{R}_{\text{200}}$ of the cluster dark matter halo, we find an extremely steep decline in the halo gas content of infalling haloes and subhaloes irrespective of cluster mass, possibly indicating the presence of an accretion shock. We also find that subhaloes are particularly gas-poor, even in the cluster outskirts, which could indicate active regions of ongoing pre-processing. By modelling the instantaneous ram pressure experienced by each halo and subhalo at $z=0$, we show that the ram pressure intensity is also well correlated with phase-space position, which is again irrespective of cluster mass. In fact, we show that regions in the phase-space plane with high differential velocity between a halo or subhalo and its local gas environment, are almost mutually exclusive with high halo gas content regions. This suggests a causal link between the gas content of objects and the instantaneous ram pressure they experience, where the dominant factor is the differential velocity.

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