Y. Ascasibar

Haloes gone MAD: The Halo-Finder Comparison Project

We present a detailed comparison of fundamental dark matter halo properties retrieved by a substantial number of different halo finders. These codes span a wide range of techniques including friends-of-friends, spherical-overdensity and phase-space-based algorithms. We

On the physical origin of dark matter density profiles

The radial mass distribution of dark matter haloes is investigated within the framework of the spherical infall model. We present a new formulation of spherical collapse including non-radial motions, and compare the analytical profiles with a set of high-resolution N-body simulations ranging from galactic to cluster scales. We argue that the dark matter density profile is entirely determined by the initial conditions, which are described by only two parameters: the height of the primordial peak and the smoothing scale. These are physically meaningful quantities in our model, related to the mass and formation time of the halo. Angular momentum is dominated by velocity dispersion, and it is responsible for the shape of the density profile near the centre. The phase-space density of our simulated haloes is well described by a power-law profile, ρ/σ 3 = 10 1.46±0.04 (ρ c /υ 3 vir) (r/r vir ) -1.90±0.05 . Setting the eccentricity of particle orbits according to the numerical results, our model is able to reproduce the mass distribution of individual haloes within 20 per cent accuracy.

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 in the presence and location of substructure and even for properties relating to the inner 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 the basic properties (mass and 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.

The radial structure of galaxy groups and clusters

ABSTRACT Simple self-consistent models of galaxy groups and clusters are tested against the re-sults of high-resolutionadiabatic gasdynamicalsimulations. We investigate two modelsbased on the existence of a ’universal’ dark matter density profile and two versionsof the beta-model. The mass distribution of relaxed clusters can be fitted by phe-nomenological formulae proposed in the literature. Haloes that have experienced arecent merging event are systematically less concentrated and show steeper profilesthan relaxed objects near the centre. The hot X-ray emitting gas is found to be inapproximate hydrostatic equilibrium with the dark matter potential, and it is welldescribed by a polytropic equation of state. Analytic formulae for the gas densityand temperature can be derived from these premises. Though able to reproduce theX-ray surface brightness, the beta-model is shown to provide a poor description ofour numerical clusters. We find strong evidence of a ’universal’ temperature profilethat decreases by a factor of 2 − 3 from the centre to the virial radius. We claimthat the spherically-averaged profiles of all physical properties of galaxy groups andclusters can be fitted with only two free parameters. Numerical resolution and entropyconservation play a key role in the shapes of the simulated profiles at small radii.Key words: galaxies: clusters: general — cosmology: theory — methods: N-bodysimulations

Shape of the oxygen abundance profiles in CALIFA face-on spiral galaxies

We measured the gas abundance profiles in a sample of 122 face-on spiral galaxies observed by the CALIFA survey and included all spaxels whose line emission was consistent with star formation. This type of analysis allowed us to improve the statistics with respect to previous studies, and to properly estimate the oxygen distribution across the entire disc to a distance of up to 3-4 disc effective radii (r

Secondary infall and dark matter haloes

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LOCALIZED STARBURSTS IN DWARF GALAXIES PRODUCED BY THE IMPACT OF LOW-METALLICITY COSMIC GAS CLOUDS

). We confirm the results obtained from classical HII region analysis. In addition to the general negative gradient, an outer flattening can be observed in the oxygen abundance radial profile. An inner drop is also found in some cases. There is a common abundance gradient between 0.5 and 2.0 r

Extremely Metal-Poor Galaxies: The Hi Content

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Subhaloes gone Notts: spin across subhaloes and finders

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Numerical simulations of the cosmic star formation history

\alpha_{O/H} = -\,0.075\,\rm{dex}/r_e