Céline Combet

DARK MATTER ANNIHILATION and DECAY PROFILES for the RETICULUM II DWARF SPHEROIDAL GALAXY

The dwarf spheroidal galaxies (dSph) of the Milky Way are among the most attractive targets for indirect searches of dark matter. In this work, we reconstruct the dark matter annihilation (J-factor) and decay profiles for the newly discovered dSph Reticulum II. Using an optimized spherical Jeans analysis of kinematic data obtained from the Michigan/Magellan Fiber System (M2FS), we find Reticulum IIs J-factor to be among the largest of any Milky Way dSph. We have checked the robustness of this result against several ingredients of the analysis. Unless it suffers from tidal disruption or significant inflation of its velocity dispersion from binary stars, Reticulum II may provide a unique window on dark matter particle properties.

Transit Flow Models for Low- and High-Mass Protostars

In this work, the gas infall and the formation of outflows around low- and high-mass protostars are investigated. A radial self-similar approach to model the transit of the molecular gas around the central object is employed. We include gravitational and radiative fields to produce heated pressure-driven outflows with magnetocentrifugal acceleration and collimation. Outflow solutions with negligible or vanishing magnetic fields are reported. They indicate that thermodynamics is a sufficient engine to generate an outflow. The magnetized solutions show dynamically significant differences in the axial region, precisely where the radial velocity and collimation are the largest. They compare quantitatively well with observations. The influence of the opacity on the transit solutions is also studied. It is found that, when dust is not the dominant coolant, such as in the primordial universe, mass infall rates have substantial larger values in the equatorial region. This suggests that stars forming in a dust-free environment should be able to accrete much more mass and become more massive than present-day protostars. It is also suggested that molecular outflows may be dominated by the global transit of material around the protostar during the very early stages of star formation, especially in the case of massive or dust-free star formation.

Star Formation Histories

The present article addresses the problem of the formation of both low and high mass stars. We suggest how competing factors change the behaviours of proto‐stellar sources and outflows in both cases. We also describe a possible temporal sequence for flows around a protostar, that may help to give a physical justification to the empirical classification of pre‐main sequence sources.

CLUMPY v3: γ-ray and ν signals from dark matter at all scales

Abstract We present the third release of the CLUMPY code for calculating γ -ray and ν signals from annihilations or decays in dark matter structures. This version includes the mean extragalactic signal with several pre-defined options and keywords related to cosmological parameters, mass functions for the dark matter structures, and γ -ray absorption up to high redshift. For more flexibility and consistency, dark matter halo masses and concentrations are now defined with respect to a user-defined overdensity Δ . We have also made changes for the user’s benefit: distribution and versioning of the code via git , less dependencies and a simplified installation, better handling of options in run command lines, consistent naming of parameters, and a new Sphinx documentation at http://lpsc.in2p3.fr/clumpy/ . Program summary Program Title: CLUMPY Program Files doi: http://dx.doi.org/10.17632/4n33mbh9bc.1 Licensing provisions: GPLv2 Programming language: C/C++ External routines/libraries: GSL ( http://www.gnu.org/software/gsl ), cfitsio ( http://heasarc.gsfc.nasa.gov/fitsio/fitsio.html ), CERN ROOT ( http://root.cern.ch ; optional, for interactive figures and stochastic simulation of halo substructures), GreAT ( http://lpsc.in2p3.fr/great ; optional, for MCMC Jeans analyses) Nature of problem: Calculation of the γ -ray and ν signals from dark matter annihilation/decay at any redshift z . Solution method: New in this release: Numerical integration of moments (in redshift and mass) of the mass function, absorption, and intensity multiplier (related to the DM density along the line of sight). Restrictions: Secondary radiation from dark matter leptons, which depends on astrophysical ingredients (radiation fields in the Universe) is the last missing piece to provide a full description of the expected signal.

Dark matter annihilation and decay factors in the Milky Way's dwarf spheroidal galaxies

The Milky Way’s dwarf spheroidal (dSph) galaxies are among the best targets for the indirect detection of dark matter (DM) from annihilation (resp. decay) products. The expected gammaray flux depends on the so-called ‘J-factor’ (resp. ‘D-factor’), the integral of the squared DM density (resp. DM density) along the line-of-sight. Using a large number of simulated dSphs, we define an optimized Jeans analysis setup for the reconstruction of the DM density with stellarkinematic data. Employing this setup, we provide estimates of astrophysical Jand D-factors for twenty-two Galactic dSphs, including the newly discovered Reticulum II. We finally identify several criteria that may indicate a contamination of a kinematic dataset by interlopers, leading to unreliable astrophysical factors. We find that the kinematic sample of Segue I, one of the closest dSph, might be affected by this issue.

Virtual MHD Jets on Grids

As network performance has outpaced computational power and storage capacity, a new paradigm has evolved to enable the sharing of geographically distributed resources. This paradigm is known as Grid computing and aims to offer access to distributed resource irrespective of their physical location. Many national, European and international projects have been launched during the last years trying to explore the Grid and to change the way we are doing our everyday work. In Ireland, we have started the CosmoGrid project that is a collaborative project aimed to provide high performance super-computing environments. This will help to address complex problems such as magnetohydrodynamic outflows and jets in order to model and numerically simulate them. Indeed, the numerical modeling of plasma jets requires massive computations, due to the wide range of spatial-temporal scales involved. We present here the first jet simulations and their corresponding models that could help to understand results from laboratory experiments.

Effects of Magnetic Field and Opacity on Self-Similar YSO Flow Models

During star formation, both infall and outflows are present around protostellar cores. Here we show solutions of a self-similar model that study the two flows with only one set of equations. We focus here on the effects of magnetic field and dust on solutions. Unmagnetized solutions have also been found. This shows that magnetic field is not the main driving mechanism of the circulation process. We have found that a reduction of magnetic field produces denser, slower and narrower outflows. When the opacity is less dominated by dust, density increases in the equatorial region, allowing larger accretion rates to occur. The comprehension of massive star formation could be related to this latter effect.