Metal enrichment of the intracluster medium: A three-dimensional picture of chemical and dynamical properties

We develop a model for the metal enrichment of the intracluster medium (ICM) that combines a cosmological non-radiative hydrodynamical N-body/SPH (smoothed particle hydrodynamic) simulation of a cluster of galaxies, and a semi-analytic model of galaxy formation. The novel feature of our hybrid model is that the chemical properties of the diffuse gas in the underlying simulation are dynamically and consistently generated from stars in the galaxies. We follow the production of several chemical elements, provided by low- and intermediate-mass stars, core collapse and Type Ia supernovae. We analyse the spatial distribution of metals in the ICM, investigate the way in which the chemical enrichment proceeds and use iron emissivity as a tracer of gas motions. The similar abundance patterns developed by O and Fe indicate that both types of supernovae pollute the ICM in a similar fashion. Their radial abundance profiles are enhanced in the inner in the last Gyr because of the convergence of enriched gas clumps to the cluster centre; this increment cannot be explained by the metal ejection of cluster galaxies which is quite low at the present epoch. Our results support a scenario in which part of the central intracluster gas comes from gas clumps that, in the redshift range of z∼ 0.2 to 0.5, have been enriched to solar values and are at large distances from the cluster centre (from ∼1 to 6 h-1 Mpc) moving at very high velocities (from ∼1300 to 2500 km s-1). The turbulent gas motions within the cluster, originated in the inhomogeneous gas infall during the cluster assembly, are manifested in emission-weighted velocity maps as gradients that can be as large as over distances of a few hundred kpc. Gradients of this magnitude are also seen in velocity distributions along sightlines through the cluster centre. Doppler shifting and broadening suffered by the Fe K α 6.7-keV emission line along such sightlines could be used to probe these gas large-scale motions when they are produced within an area characterized by high iron line emissivity.Facultad de Ciencias Astronómicas y Geofísica

Thousands of milky ways: Galaxy satellites and building blocks

A semi-analytic model of galaxy formation with and without active galactic nuclei feedback is used to study the nature of possible building blocks (BBs) of z = 0 galaxies, including those of Milky-Way types. We find that BBs can show an important range of properties arising from environmental variables such as host halo mass, and whether a galaxy is a satellite within its host halo; the stellar formation histories are comparatively faster and the chemical enrichment is more efficient in BBs than in surviving satellites, in accordance with recent metallicity measurements for the Milky Way. These results can be used in combination with observational constraints to continue probing the ability of the cold dark-matter scenario to reproduce the history of galaxy demography in the Universe.Instituto de Astrofísica de La Plat

On the effect of chaotic orbits on dynamical friction

Chaotic orbits suffer significant changes as a result of small perturbations. One can thus wonder whether the dynamical friction suffered by a satellite on a regular orbit, and interacting with the stars of a galaxy, will be different if the bulk of the stars of the galaxy are in regular or chaotic orbits. In order to check that idea, we investigated the orbital decay (caused by dynamical friction) of a rigid satellite moving within a larger stellar system (a galaxy) whose potential is nonintegrable. We performed numerical experiments using two kinds of triaxial galaxy models: (1) the triaxial generalization of Dehnen´s spherical mass model (Dehnen; Merritt & Fridman); (2) a modified Satoh model (Satoh; Carpintero, Muzzio, & Wachlin). The percentages of chaotic orbits present in these models were increased by perturbing them. In the first case, a central compact object (black hole) was introduced; in the second case, the perturbation was produced by allowing the galaxy to move on a circular orbit in a logarithmic potential. The equations of motion were integrated with a non-self-consistent code. Our results show that the presence of chaotic orbits does not affect significantly the orbital decay of the satellite.Instituto de Astrofísica de La Plat

On the dynamical origin of the ICM metallicity evolution

We present a study on the origin of the metallicity evolution of the intra-cluster medium (ICM) by applying a semi-analytic model of galaxy formation to N-body/smoothed particle hydrodynamic (SPH) non-radiative numerical simulations of clusters of galaxies. The semi-analytic model includes gas cooling, star formation, supernovae feedback and metal enrichment, and is linked to the diffuse gas of the underlying simulations so that the chemical properties of gas particles are dynamically and consistently generated from stars in the galaxies. This hybrid model lets us have information on the spatial distribution of metals in the ICM. The results obtained for a set of clusters with virial masses of ∼1.5 × 1015 h−1 M contribute to the theoretical interpretation of recent observational X-ray data, which indicate a decrease of the average iron content of the intra-cluster gas with increasing redshift. We find that this evolution arises mainly as a result of a progressive increase of the iron abundance within ∼0.15 Rvir. The clusters have been considerably enriched by z ∼ 1 with very low contribution from recent star formation. Low entropy gas that has been enriched at high redshift sinks to the cluster centre contributing to the evolution of the metallicity profiles.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Ram pressure profiles in galaxy groups and clusters

Using a hybrid method that combines non-radiative hydrodynamical simulations with a semianalytic model of galaxy formation, we determine the ram pressure experienced by galaxies in haloes with virial masses 12.5 ≤ log (M200/ h−1 M⊙) < 15.35 as a function of the halocentric distance, for redshifts 0 ≤ z ≤ 3. The ram pressure is calculated with a self-consistent method that uses the simulation gas particles to obtain the properties of the intergalactic medium. The ram pressure profiles obtained can be well described by beta profile models, with parameters that depend on redshift and halo virial mass in a simple fashion. The fitting formulae provided here will prove useful to include ram pressure effects into semi-analytic models based on methods that lack gas physics, such as dark-matter-only simulations or the Press–Schechter formalism.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica

On the dynamical origin of the ICM metallicity evolution

We present a study on the origin of the metallicity evolution of the intra-cluster medium (ICM) by applying a semi-analytic model of galaxy formation to N-body/smoothed particle hydrodynamic (SPH) non-radiative numerical simulations of clusters of galaxies. The semi-analytic model includes gas cooling, star formation, supernovae feedback and metal enrichment, and is linked to the diffuse gas of the underlying simulations so that the chemical properties of gas particles are dynamically and consistently generated from stars in the galaxies. This hybrid model lets us have information on the spatial distribution of metals in the ICM. The results obtained for a set of clusters with virial masses of ∼1.5 × 1015 h−1 M contribute to the theoretical interpretation of recent observational X-ray data, which indicate a decrease of the average iron content of the intra-cluster gas with increasing redshift. We find that this evolution arises mainly as a result of a progressive increase of the iron abundance within ∼0.15 Rvir. The clusters have been considerably enriched by z ∼ 1 with very low contribution from recent star formation. Low entropy gas that has been enriched at high redshift sinks to the cluster centre contributing to the evolution of the metallicity profiles.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Non-thermal processes in the cluster of galaxies Abell 3376

We model the high-energy emission that results from the interaction of relativistic particles with photons and matter in the cluster of galaxies Abell 3376. The presence of relativistic particles is inferred from the recently found radio relics in this cluster, being one of the most prominent examples of double opposite, giant ring-like radio structures. Assuming that diffusive shock acceleration takes place in the cluster regions where radio relics are observed, we calculate the spectral energy distribution resulting from the most relevant non-thermal processes, which are synchrotron radiation, inverse-Compton scattering, relativistic Bremsstrahlung and inelastic proton-proton collisions. In the context of our model, the major radiative component at high energies is inverse-Compton scattering, which could reach luminosities L ∼ 9 × 1041 erg s-1 in the energy range between ∼1 MeV and 10 TeV. Hadronic interactions would yield a minor contribution to the overall non-thermal emission, but would dominate at ultrahigh energies. The cluster Abell 3376 might be detectable at gamma-rays by HESS, GLAST satellite and future planned Cherenkov arrays.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La PlataInstituto Argentino de Radioastronomí

Ram pressure profiles in galaxy groups and clusters

Using a hybrid method that combines non-radiative hydrodynamical simulations with a semianalytic model of galaxy formation, we determine the ram pressure experienced by galaxies in haloes with virial masses 12.5 ≤ log (M200/ h−1 M⊙) < 15.35 as a function of the halocentric distance, for redshifts 0 ≤ z ≤ 3. The ram pressure is calculated with a self-consistent method that uses the simulation gas particles to obtain the properties of the intergalactic medium. The ram pressure profiles obtained can be well described by beta profile models, with parameters that depend on redshift and halo virial mass in a simple fashion. The fitting formulae provided here will prove useful to include ram pressure effects into semi-analytic models based on methods that lack gas physics, such as dark-matter-only simulations or the Press–Schechter formalism.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica

Non-thermal processes in the cluster of galaxies Abell 3376

We model the high-energy emission that results from the interaction of relativistic particles with photons and matter in the cluster of galaxies Abell 3376. The presence of relativistic particles is inferred from the recently found radio relics in this cluster, being one of the most prominent examples of double opposite, giant ring-like radio structures. Assuming that diffusive shock acceleration takes place in the cluster regions where radio relics are observed, we calculate the spectral energy distribution resulting from the most relevant non-thermal processes, which are synchrotron radiation, inverse-Compton scattering, relativistic Bremsstrahlung and inelastic proton-proton collisions. In the context of our model, the major radiative component at high energies is inverse-Compton scattering, which could reach luminosities L ∼ 9 × 1041 erg s-1 in the energy range between ∼1 MeV and 10 TeV. Hadronic interactions would yield a minor contribution to the overall non-thermal emission, but would dominate at ultrahigh energies. The cluster Abell 3376 might be detectable at gamma-rays by HESS, GLAST satellite and future planned Cherenkov arrays.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La PlataInstituto Argentino de Radioastronomí

Discontinuity in multipolar expansions

We show that softening does not avoid discontinuities in some multipolar expansions, but they do not affect the results of numerical integrations of the N-body problem.Asociación Argentina de Astronomí