arXiv subjects

Edoardo Carlesi

Publications and source records attributed to Edoardo Carlesi.

17 recordsLinked to original sources

arXiv2022

Estimation of the masses in the Local Group by Gradient Boosted Decision Trees

Our goal is to estimate the mass of the Local Group (LG) and the individual masses of its primary galaxies, the M31 and the Milky Way (MW). We do this by means of a supervised machine learning algorithm, the gradient boosted decision trees (GBDT) and using the observed distance and relative velocity of the two as input parameters. The GBDT is applied to a sample of 2148 mock LGs drawn from a set of 5 dark matter (DM)-only simulations, ran within the standard $Λ$CDM\ cosmological model. The selection of the mock LGs is guided by a LG model, which defines such objects. The role of the observational uncertainties of the input parameters is gauged by applying the model to an ensemble of mock LGs pairs whose observables are these input parameters perturbed by their corresponding observational errors. Finally the observational data of the actual LG is used to infer its relevant masses. Our main results are the sum and the individual masses of the MW and M31: $M_{tot} = 3.31 ^{+0.79}_{-0.67} $, $M_{MW}=1.15^{+0.25}_{-0.22}$ and $M_{M31}=2.01^{+0.65}_{-0.39} \ \ \times 10^{12}M_{\odot}$ (corresponding to the median and the 1st and 3rd quartiles). The ratio of the masses is $M_{M31}/M_{MW}=1.75^{+0.54}_{-0.28}$, where by convention the M31 is defined here to be the more massive of the two halos.

astro-ph.CO↗

arXiv2020

The Hestia project: simulations of the Local Group

We present the Hestia simulation suite: High-resolutions Environmental Simulations of The Immediate Area, a set of cosmological simulations of the Local Group. Initial conditions constrained by the observed peculiar velocity of nearby galaxies are employed to accurately simulate the local cosmography. Halo pairs that resemble the Local Group are found in low resolutions constrained, dark matter only simulations, and selected for higher resolution magneto hydrodynamic simulation using the Arepo code. Baryonic physics follows the Auriga model of galaxy formation. The simulations contain a high resolution region of 3-5 Mpc in radius from the Local Group midpoint embedded in the correct cosmographic landscape. Within this region a simulated Local Group consisting of a Milky Way and Andromeda like galaxy forms, whose description is in excellent agreement with observations. The simulated Local Group galaxies resemble the Milky Way and Andromeda in terms of their halo mass, mass ratio, stellar disc mass, morphology separation, relative velocity, rotation curves, bulge-disc morphology, satellite galaxy stellar mass function, satellite radial distribution and in some cases, the presence of a Magellanic cloud like object. Because these simulations properly model the Local Group in their cosmographic context, they provide a testing ground for questions where environment is thought to play an important role.

astro-ph.GA↗

arXiv2019

On the Mass Assembly History of the Local Group

In this work an ensemble of simulated Local Group analogues is used to constrain the properties of the mass assembly history of the Milky Way (MW) and Andromeda (M31) galaxies. These objects have been obtained using the constrained simulation technique, which ensures that simulated LGs live within a large scale environment akin to the observed one. Our results are compared against a standard $Λ$ Cold Dark Matter ($Λ$CDM) series of simulations which use the same cosmological parameters. This allows us to single out the effects of the constraints on the results. We find that (a) the median constrained merging histories for M31 and MW live above the standard ones at the 1-$σ$ level, (b) the median formation time takes place $\approx$ 0.5 Gyr earlier than unconstrained values, while the latest major merger happens on average 1.5 Gyr earlier and (c) the probability for both LG haloes to have experienced their last major merger in the first half of the history of the Universe is $\approx$ 50% higher for the constrained pairs. These results have been estimated to be significant at the 99% confidence level by means of a Kolmogorov-Simirnov test. These results suggest that the particular environment in which the Milky Way and Andromeda form plays a role in shaping their properties, and favours earlier formation and last major merger time values in agreement with other observational and theoretical considerations.

astro-ph.GA↗

arXiv2019

The orientation of planes of dwarf galaxies in the quasi-linear Universe

To date at least 10 highly flattened planes of dwarf galaxies are claimed to have been discovered in the Local Universe. The origin of these planes of galaxies remains unknown. One suggestion is that they are related to the large-scale structure of the cosmic web. A recent study found that the normal of a number of these dwarf galaxy planes are very closely aligned with the eigenvector of the shear tensor corresponding to the direction of greatest collapse obtained by reconstructing the full velocity field in the linear regime. Here we extend that work by both considering an additional 5 planes beyond the 5 examined previously and by examining the alignment with respect to the quasi-linear field, a more sophisticated reconstruction, which is a better approximation on smaller (quasi-linear) scales. Our analysis recovers the previous result while not finding a significantly tight alignment with the additional 5 planes. However, the additional 5 planes normals also do not appear to be randomly oriented. We conclude that this could either be due to the normals of the new planes being poorly defined and described; the quasi-linear field at those locations being poorly constrained; or different formation mechanisms for the orientation of planes of dwarf galaxies.

astro-ph.GA↗

arXiv2018

Cosmic-Ray Anisotropy from Large Scale Structure and the effect of magnetic horizons

Motivated by the ~7 % dipole anisotropy in the distribution of ultra-high energy cosmic-rays (UHECRs) above 8 EeV, we explore the anisotropy induced by the large scale structure, using constrained simulations of the local Universe and taking into account the effect of magnetic fields. The value of the intergalactic magnetic field (IGMF) is critical as it determines the UHECR cosmic horizon. We calculate the UHECR sky maps for different values of the IGMF variance and show the effect of the UHECR horizon on the observed anisotropy. The footprint of the local ($\lesssim350$ Mpc) Universe on the UHECR background, a small angular scale enhancement in the Northern Hemisphere, is seen. At 11.5 EeV (the median value of the energy bin at which the dipole has been reported), the LSS-induced dipole amplitude is $A_1\sim10\%$, for IGMF in the range [0.3-3] nG for protons, helium and nitrogen, compatible with the rms value derived from the cosmic power spectrum. However at these energies the UHECRs are also influenced by the Galactic Magnetic Field (GMF) and we discuss its effect on the LSS-induced anisotropy.

astro-ph.HE↗

arXiv2018

The quasi-linear nearby Universe

The local Universe provides a unique opportunity for testing cosmology and theories of structure formation. To facilitate this opportunity we present a new method for the reconstruction of the quasi-linear matter density and velocity fields from galaxy peculiar velocities and apply it to the Cosmicflows-2 data. The method consists of constructing an ensemble of cosmological simulations, constrained by the standard cosmological model and the observational data. The quasi-linear density field is the geometric mean and variance of the fully non-linear density fields of the simulations. The main nearby clusters (Virgo, Centaurus, Coma), superclusters (Shapley, Perseus-Pisces) and voids (Dipole Repeller) are robustly reconstructed. Galaxies are born biased with respect to the underlying dark matter distribution. Using our quasi-linear framework we demonstrate that the luminosity-weighted density field derived from the 2M++ redshift compilations is non-linearly biased with respect to the matter density field. The bias diminishes in the linear regime.

astro-ph.CO↗

arXiv2017

The dynamics of the local group as a probe of Dark Energy and Modified Gravity

In this work we study the dynamics of the Local Group (LG) within the context of cosmological models beyond General Relativity (GR). Using observable kinematic quantities to identify candidate pairs we build up samples of simulated LG-like objects drawing from $f(R)$, symmetron, DGP and quintessence N-body simulations together with their $Λ$CDM counterparts featuring the same initial random phase realisations. The variables and intervals used to define LG-like objects are referred to as Local Group model; different models are used throughout this work and adapted to study their dynamical and kinematic properties. The aim is to determine how well the observed LG-dynamics can be reproduced within cosmological theories beyond GR, We compute kinematic properties of samples drawn from alternative theories and $Λ$CDM and compare them to actual observations of the LG mass, velocity and position. As a consequence of the additional pull, pairwise tangential and radial velocities are enhanced in modified gravity and coupled dark energy with respect to $Λ$CDM, inducing significant changes to the total angular momentum and energy of the LG. For example, in models such as $f(R)$ and the symmetron this increase can be as large as $60\%$, peaking well outside of the $95\%$ confidence region allowed by the data. This shows how simple considerations about the LG dynamics can lead to clear small-scale observational signatures for alternative scenarios, without the need of expensive high-resolution simulations.

astro-ph.CO↗

arXiv2016

Constraining the mass of the Local Group

The mass of the Local Group (LG) is a crucial parameter for galaxy formation theories. However, its observational determination is challenging - its mass budget is dominated by dark matter which cannot be directly observed. To meet this end the posterior distributions of the LG and its massive constituents have been constructed by means of constrained and random cosmological simulations. Two priors are assumed - the LCDM model that is used to set up the simulations and a LG model,which encodes the observational knowledge of the LG and is used to select LG-like objects from the simulations. The constrained simulations are designed to reproduce the local cosmography as it is imprinted onto the Cosmicflows-2 database of velocities. Several prescriptions are used to define the LG model, focusing in particular on different recent estimates of the tangential velocity of M31. It is found that (a) different $v_{tan}$ choices affect the peak mass values up to a factor of 2, and change mass ratios of $M_{M31}$ to $M_{MW}$ by up to 20%; (b) constrained simulations yield more sharply peaked posterior distributions compared with the random ones; (c) LG mass estimates are found to be smaller than those found using the timing argument; (d) preferred MW masses lie in the range of $(0.6 - 0.8)\times10^{12} M_{\odot}$ whereas (e) $M_{M31}$ is found to vary between $(1.0 - 2.0)\times10^{12} M_{\odot}$, with a strong dependence on the $v_{tan}$ values used.

astro-ph.GA↗

arXiv2016

The tangential velocity of M31: CLUES from constrained simulations

Determining the precise value of the tangential component of the velocity of M31 is a non trivial astrophysical issue, that relies on complicated modeling. This has recently lead to con- flicting estimates, obtained by several groups that used different methodologies and assump- tions. This letter addresses the issue by computing a Bayesian posterior distribution function of this quantity, in order to measure the compatibility of those estimates with LambdaCDM. This is achieved using an ensemble of local group (LG) look-alikes collected from a set of Con- strained Simulations (CSs) of the local Universe, and a standard unconstrained LambdaCDM. The latter allows us to build a control sample of LG-like pairs and to single out the influence of the environment in our results. We find that neither estimate is at odds with LambdaCDM; how- ever, whereas CSs favour higher values of vtan , the reverse is true for estimates based on LG samples gathered from unconstrained simulations, overlooking the environmental element

astro-ph.GA↗

arXiv2016

Constrained Local UniversE Simulations: A Local Group Factory

Near field cosmology is practiced by studying the Local Group (LG) and its neighbourhood. The present paper describes a framework for simulating the near field on the computer. Assuming the LCDM model as a prior and applying the Bayesian tools of the Wiener filter (WF) and constrained realizations of Gaussian fields to the Cosmicflows-2 (CF2) survey of peculiar velocities, constrained simulations of our cosmic environment are performed. The aim of these simulations is to reproduce the LG and its local environment. Our main result is that the LG is likely a robust outcome of the LCDM scenario when subjected to the constraint derived from CF2 data, emerging in an environment akin to the observed one. Three levels of criteria are used to define the simulated LGs. At the base level, pairs of halos must obey specific isolation, mass and separation criteria. At the second level the orbital angular momentum and energy are constrained and on the third one the phase of the orbit is constrained. Out of the 300 constrained simulations 146 LGs obey the first set of criteria, 51 the second and 6 the third. The robustness of our LG factory enables the construction of a large ensemble of simulated LGs. Suitable candidates for high resolution hydrodynamical simulations of the LG can be drawn from this ensemble, which can be used to perform comprehensive studies of the formation of the LG

astro-ph.CO↗

arXiv2015

Cosmicflows Constrained Local UniversE Simulations

This paper combines observational datasets and cosmological simulations to generate realistic numerical replicas of the nearby Universe. These latter are excellent laboratories for studies of the non-linear process of structure formation in our neighborhood. With measurements of radial peculiar velocities in the Local Universe (cosmicflows-2) and a newly developed technique, we produce Constrained Local UniversE Simulations (CLUES). To assess the quality of these constrained simulations, we compare them with random simulations as well as with local observations. The cosmic variance, defined as the mean one-sigma scatter of cell-to-cell comparison between two fields, is significantly smaller for the constrained simulations than for the random simulations. Within the inner part of the box where most of the constraints are, the scatter is smaller by a factor 2 to 3 on a 5 Mpc/h scale with respect to that found for random simulations. This one-sigma scatter obtained when comparing the simulated and the observation-reconstructed velocity fields is only 104 +/- 4 km/s i.e. the linear theory threshold. These two results demonstrate that these simulations are in agreement with each other and with the observations of our neighborhood. For the first time, simulations constrained with observational radial peculiar velocities resemble the Local Universe up to a distance of 150 Mpc/h on a scale of a few tens of megaparsecs. When focusing on the inner part of the box, the resemblance with our cosmic neighborhood extends to a few megaparsecs (< 5 Mpc/h). The simulations provide a proper Large Scale environment for studies of the formation of nearby objects.

astro-ph.CO↗

arXiv2015

Hidden from view: Coupled Dark Sector Physics and Small Scales

We study cluster mass dark matter haloes, their progenitors and surroundings in an coupled Dark Matter-Dark Energy model and compare it to quintessence and $Λ$CDM models with adiabatic zoom simulations. When comparing cosmologies with different expansions histories, growth functions & power spectra, care must be taken to identify unambiguous signatures of alternative cosmologies. Shared cosmological parameters, such as $σ_8$, need not be the same for optimal fits to observational data. We choose to set our parameters to $Λ$CDM $z=0$ values. We find that in coupled models, where DM decays into DE, haloes appear remarkably similar to $Λ$CDM haloes despite DM experiencing an additional frictional force. Density profiles are not systematically different and the subhalo populations have similar mass, spin, and spatial distributions, although (sub)haloes are less concentrated on average in coupled cosmologies. However, given the scatter in related observables ($V_{\rm max},R_{V_{\rm max}}$), this difference is unlikely to distinguish between coupled and uncoupled DM. Observations of satellites of MW and M31 indicate a significant subpopulation reside in a plane. Coupled models do produce planar arrangements of satellites of higher statistical significance than $Λ$CDM models, however, in all models these planes are dynamically unstable. In general, the nonlinear dynamics within and near large haloes masks the effects of a coupled dark sector. The sole environmental signature we find is that small haloes residing in the outskirts are more deficient in baryons than their $Λ$CDM counterparts. The lack of a pronounced signal for a coupled dark sector strongly suggests that such a phenomena would be effectively hidden from view.

astro-ph.CO↗

arXiv2014

On the observability of coupled dark energy with cosmic voids

Taking N-body simulations with volumes and particle densities tuned to match the SDSS DR7 spectroscopic main sample, we assess the ability of current void catalogs (e.g., Sutter et al. 2012b) to distinguish a model of coupled dark matter-dark energy from ΛCDM cosmology using properties of cosmic voids. Identifying voids with the VIDE toolkit, we find no statistically significant differences in the ellipticities, but find that coupling produces a population of significantly larger voids, possibly explaining the recent result of Tavasoli et al. (2013). In addition, we use the universal density profile of Hamaus et al. (2014) to quantify the relationship between coupling and density profile shape, finding that the coupling produces broader, shallower, undercompensated profiles for large voids by thinning the walls between adjacent medium-scale voids. We find that these differences are potentially measurable with existing void catalogs once effects from survey geometries and peculiar velocities are taken into account.

astro-ph.CO↗

arXiv2014

Hydrodynamical simulations of coupled and uncoupled quintessence models II: Galaxy clusters

We study the $z=0$ properties of clusters (and large groups) of galaxies within the context of interacting and non-interacting quintessence cosmological models, using a series of adiabatic SPH simulations. Initially, we examine the average properties of groups and clusters, quantifying their differences in LCDM, uncoupled Dark Energy (\ude) and coupled Dark Energy (\cde) cosmologies. In particular, we focus upon radial profiles of the gas density, temperature and pressure, and we also investigate how the standard hydrodynamic equilibrium hypothesis holds in quintessence cosmologies. While we are able to confirm previous results about the distribution of baryons, we also find that the main discrepancy (with differences up to $20\%$) can be seen in cluster pressure profiles. We then switch attention to individual structures, mapping each halo in quintessence cosmology to its \LCDM\ counterpart. We are able to identify a series of small correlations between the coupling in the dark sector and halo spin, triaxiality and virialization ratio. When looking at spin and virialization of dark matter haloes, we find a weak ($5\%$) but systematic deviation in fifth force scenarios from \LCDM.

astro-ph.CO↗

arXiv2014

Hydrodynamical simulations of coupled and uncoupled quintessence models I: Halo properties and the cosmic web

We present the results of a series of adiabatic hydrodynamical simulations of several quintessence models (both with a free and an interacting scalar field) in comparison to a standard \LCDM\ cosmology. For each we use $2\times1024^3$ particles in a $250$\hMpc\ periodic box assuming WMAP7 cosmology. In this work we focus on the properties of haloes in the cosmic web at $z=0$. The web is classified into \emph{voids}, \emph{sheets}, \emph{filaments} and \emph{knots} depending on the eigenvalues of the velocity shear tensor, which are an excellent proxy for the underlying overdensity distribution. We find that the properties of objects classified according to their surrounding environment shows a substantial dependence on the underlying cosmology; for example, while $V_{\rm max}$ shows average deviations of $\approx5$ per cent across the different models when considering the full halo sample, comparing objects classified according to their environment, the size of the deviation can be as large as $20$ per cent. We also find that halo spin parameters are positively correlated to the coupling, whereas halo concentrations show the opposite behaviour. Furthermore, when studying the concentration-mass relation in different environments, we find that in all cosmologies underdense regions have a larger normalization and a shallower slope. While this behaviour is found to characterize all the models, differences in the best-fit relations are enhanced in (coupled) dark energy, thus providing a clearer prediction for this class of models.

astro-ph.CO↗

arXiv2013

Vector dark energy and high-z massive clusters

The detection of extremely massive clusters at $z>1$ such as SPT-CL J0546-5345, SPT-CL J2106-5844, and XMMU J2235.3-2557 has been considered by some authors as a challenge to the standard \LCDM$\;$cosmology. In fact,assuming Gaussian initial conditions, the theoretical expectation of detecting such objects is as low as $\leq 1%$. In this \textit{Letter} we discuss the probability of the existence of such objects in the light of the Vector Dark Energy (VDE) paradigm, showing by means of a series of $N$-body simulations that chances of detection are substantially enhanced in this non-standard framework.

astro-ph.CO↗

arXiv2013

N-body simulations with a cosmic vector for dark energy

We present the results of a series of cosmological $N$-body simulations of a Vector Dark Energy (VDE) model, performed using a suitably modified version of the publicly available \texttt{GADGET}-2 code. The setups of our simulations were calibrated pursuing a twofold aim: 1) to analyze the large scale distribution of massive objects and 2) to determine the properties of halo structure in this different ramework.We observe that structure formation is enhanced in VDE, since the mass function at high redshift is boosted up to a factor of ten with respect to \LCDM, possibly alleviating tensions with the observations of massive clusters at high redshifts and early reionization epoch. Significant differences can also be found for the value of the growth factor, that in VDE shows a completely different behaviour, and in the distribution of voids, which in this cosmology are on average smaller and less abundant. We further studied the structure of dark matter haloes more massive than $5\times10^{13}$\hMsun, finding that no substantial difference emerges when comparing spin parameter, shape, triaxiality and profiles of structures evolved under different cosmological pictures. Nevertheless, minor differences can be found in the concentration-mass relation and the two point correlation function; both showing different amplitudes and steeper slopes.Using an additional series of simulations of a \LCDM\ scenario with the same $Ω_M$ and $σ_8$ used in the VDE cosmology, we have been able to establish whether the modifications induced in the new cosmological picture were due to the particular nature of the dynamical dark energy or a straightforward consequence of the cosmological parameters.

astro-ph.CO↗