arXiv subjects

Manuel E. Merchán

Publications and source records attributed to Manuel E. Merchán.

5 recordsLinked to original sources

arXiv2020

Detection and analysis of cluster-cluster filaments

In this work, we identify and analyse the properties of cluster-cluster filaments within a cosmological simulation assuming that they are structures connecting maxima of the density field defined by dark matter halos with masses $M \, \ge 10^{14}\, h^{-1} \mathrm{M_{\odot}}$. To extract these filaments we develop an identification algorithm based on two standard tools: the Minimal Spanning Tree (MST) and the Friends of Friends (FoF) algorithm. Focusing our analysis on the densest dark matter filaments, we found that the radial density profile, at scales around $1\, h^{-1} \mathrm{Mpc}$, approximately follow a power-law function with index -2. Without making any assumption about the velocity field, our algorithm finds that the saddle point arises as a natural characteristic of the filamentary structure. In addition, its location along the filament depends on the masses of the halos at the filament ends. We also found that the infall velocities follow a cross-pattern near the saddle point, being perpendicular to the filament spine when approaching from low-density regions, and parallel away from the saddle point towards the ends of the filament. Following theoretical prescriptions, we estimate the linear density from the transverse velocity dispersion, finding a good correspondence with the measured mass per unit length of our filaments. Our results can be applied to observational samples of filaments in order to link the saddle point location and the mass per unit length with measurements obtained from observations such as cluster masses and the velocity dispersion of galaxies.

astro-ph.CO↗

arXiv2019

Deviations from tidal torque theory: environment dependences on halo angular momentum growth

The tidal torque theory (TTT) relates the origin and evolution of angular momentum with the environment in which dark matter (DM) haloes form. The deviations introduced by late non-linearities are commonly thought as noise in the model. In this work, we analyze a cosmological simulation looking for systematics on these deviations, finding that the classification of DM haloes according to their angular momentum growth results in samples with different internal alignment, spin parameter distribution and assembly history. Based on this classification, we obtain that low mass haloes are embedded in denser environments if they have acquired angular momentum below the TTT expectations (L haloes), whereas at high masses enhanced clustering is typically associated with higher angular momentum growths (W haloes). Additionally, we find that the low mass signal has a weak dependence on the direction, whereas the high mass signal is entirely due to the structure perpendicular to the angular momentum. Finally, we study the anisotropy of the matter distribution around haloes as a function of their mass. We find that the angular momentum direction of W (L) haloes remains statistically perpendicular (parallel) to the surrounding structure across the mass range $11<\mathrm{log}(M/h^{-1}\mathrm{M}_{\odot})<14$, whereas haloes following TTT show a "spin flip" mass consistent with previously reported values ($\sim 5 \times 10^{12}$ $h^{-1}\mathrm{M}_\odot$). Hence, whether the spin flip mass of the deviated samples is highly shifted or straightly undefined, our results indicate that is remarkably connected to the haloes angular momentum growth.

astro-ph.CO↗

arXiv2012

Subhaloes gone Notts: Spin across subhaloes and finders

We present a study of a comparison of spin distributions of subhaloes found associated with a host halo. The subhaloes are found within two cosmological simulation families of Milky Way-like galaxies, namely the Aquarius and GHALO simulations. These two simulations use different gravity codes and cosmologies. We employ ten different substructure finders, which span a wide range of methodologies from simple overdensity in configuration space to full 6-d phase space analysis of particles.We subject the results to a common post-processing pipeline to analyse the results in a consistent manner, recovering the dimensionless spin parameter. We find that spin distribution is an excellent indicator of how well the removal of background particles (unbinding) has been carried out. We also find that the spin distribution decreases for substructure the nearer they are to the host halo's, and that the value of the spin parameter rises with enclosed mass towards the edge of the substructure. Finally subhaloes are less rotationally supported than field haloes, with the peak of the spin distribution having a lower spin parameter.

astro-ph.CO↗

arXiv2012

SubHaloes going Notts: The SubHalo-Finder Comparison Project

We present a detailed comparison of the substructure properties of a single Milky Way sized dark matter halo from the Aquarius suite at five different resolutions, as identified by a variety of different (sub-)halo finders for simulations of cosmic structure formation. These finders span a wide range of techniques and methodologies to extract and quantify substructures within a larger non-homogeneous background density (e.g. a host halo). This includes real-space, phase-space, velocity-space and time- space based finders, as well as finders employing a Voronoi tessellation, friends-of-friends techniques, or refined meshes as the starting point for locating substructure.A common post-processing pipeline was used to uniformly analyse the particle lists provided by each finder. We extract quantitative and comparable measures for the subhaloes, primarily focusing on mass and the peak of the rotation curve for this particular study. We find that all of the finders agree extremely well on the presence and location of substructure and even for properties relating to the inner part part of the subhalo (e.g. the maximum value of the rotation curve). For properties that rely on particles near the outer edge of the subhalo the agreement is at around the 20 per cent level. We find that basic properties (mass, maximum circular velocity) of a subhalo can be reliably recovered if the subhalo contains more than 100 particles although its presence can be reliably inferred for a lower particle number limit of 20. We finally note that the logarithmic slope of the subhalo cumulative number count is remarkably consistent and <1 for all the finders that reached high resolution. If correct, this would indicate that the larger and more massive, respectively, substructures are the most dynamically interesting and that higher levels of the (sub-)subhalo hierarchy become progressively less important.

astro-ph.CO↗

arXiv2001

Redshift-Space Distortions of Group and Galaxy Correlations

The two-point correlation function is computed for galaxies and groups of galaxies selected using 3-dimensional information from the Updated Zwicky Galaxy Catalog - (UZC). The redshift space distortion of the correlation function $ξ(σ,π)$ in the directions parallel and perpendicular to the line of sight, induced by pairwise group peculiar velocities is evaluated. Two methods are used to characterize the pairwise velocity field of groups and galaxies. The best fitting parameters are $γ=-1.89 \pm 0.17$ and $r_0=9.7 \pm 4.5$ $h^{-1}$ Mpc for groups, and $γ=-2.00 \pm 0.03$ and $r_0=5.29 \pm 0.21$ $h^{-1}$ Mpc for galaxies. We find $β_{gx}=0.51 \pm 0.15$ for galaxies, while for groups we obtain a noisy estimate $β< 1.5$.

astro-ph↗