Astrophysical Ingredients Research Articles

CLUMPY v3: [formula omitted]-ray and [formula omitted] signals from dark matter at all scales

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 summaryProgram Title:CLUMPYProgram Files doi:http://dx.doi.org/10.17632/4n33mbh9bc.1Licensing provisions: GPLv2Programming 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.

Cosmic-ray propagation with DRAGON2: I. numerical solver and astrophysical ingredients

We present version 2 of the DRAGON code designed for computing realistic predictions of the CR densities in the Galaxy. The code numerically solves the interstellar CR transport equation (including inhomogeneous and anisotropic diffusion, either in space and momentum, advective transport and energy losses), under realistic conditions. The new version includes an updated numerical solver and several models for the astrophysical ingredients involved in the transport equation. Improvements in the accuracy of the numerical solution are proved against analytical solutions and in reference diffusion scenarios. The novel features implemented in the code allow to simulate the diverse scenarios proposed to reproduce the most recent measurements of local and diffuse CR fluxes, going beyond the limitations of the homogeneous galactic transport paradigm. To this end, several applications using DRAGON2 are presented as well. This new version facilitates the users to include their own physical models by means of a modular C++ structure.

Dark matter astrophysical uncertainties and the neutrino floor

The search for weakly interacting massive particles (WIMPs) by direct detection faces an encroaching background due to coherent neutrino-nucleus scattering. For a given WIMP mass the cross section at which neutrinos constitute a dominant background is dependent on the uncertainty on the flux of each neutrino source from either the Sun, supernovae or atmospheric cosmic ray collisions. However there are also considerable uncertainties with regard to the astrophysical ingredients to the predicted WIMP signal. Uncertainties in the velocity of the Sun with respect to the Milky Way dark matter halo, the local density of WIMPs, and the shape of the local WIMP speed distribution all have an effect on the expected event rate in direct detection experiments and hence will change the region of the WIMP parameter space for which neutrinos are a significant background. In this work we extend the WIMP+neutrino analysis to account for the uncertainty in the astrophysics dependence of the WIMP signal. We show the effect of uncertainties on projected discovery limits with an emphasis on low WIMP masses (less than 10 GeV) when Solar neutrino backgrounds are most important. We find that accounting for astrophysical uncertainties changes the shape of the neutrino floor as a function of WIMP mass but also causes it to appear at cross sections up to an order of magnitude larger, extremely close to existing experimental limits - indicating that neutrino backgrounds will become an issue sooner than previously thought. We also explore how neutrinos hinder the estimation of WIMP parameters and how astrophysical uncertainties impact the discrimination of WIMPs and neutrinos with the use of their respective time dependencies.

Luminosity function and radial distribution of Milky Way satellites in a ΛCDM Universe

We study the luminosity function (LF) and the radial distribution of satellite galaxies within Milky Way (MW) sized haloes as predicted in cold dark matter based models of galaxy formation, making use of numerical N-body techniques as well as three different semi-analytic models (SAMs) galaxy formation codes. We extract merger trees from very high-resolution dissipationless simulations of four Galaxy-sized DM haloes, and use these as common input for the SAMs. We present a detailed comparison of our predictions with the observational data recently obtained on the MW satellite LF. We find that SAMs with rather standard astrophysical ingredients are able to reproduce the observed LF over six orders of magnitude in luminosity, down to magnitudes as faint as MV =−2. We also perform a comparison with the actual observed number of satellites as a function of luminosity, by applying the selection criteria of the SDSS survey to our simulations instead of correcting the observations for incompleteness. Using this approach, we again find good agreement for both the luminosity and radial distributions of MW satellites. We investigate which physical processes in our models are responsible for shaping the predicted satellite LF, and find that tidal destruction, suppression of gas infall by a photoionizing background, and supernova feedback all make important contributions. We conclude that the number and luminosity of MW satellites can be naturally accounted for within the (Λ)cold dark matter paradigm, and this should no longer be considered a problem.

Stellar Activity with BRITE: the “Aurigae” field

Die Serie Communications in Asteroseismology (CoAst) stellt eine international gefragte Plattform für wissenschaftliche Publikationen der neuesten Forschungsergebnisse auf dem Gebiet der Asteroseismologie dar. Forschungsgegenstand der Asteroseismologie sind veränderliche und pulsierende Sterne. Neben den halbjährlich erscheinenden regulären Ausgaben mit Beiträgen aus der laufenden Forschung werden auch Sonderausgaben für Konferenzberichte bzw. Programmhandbücher herausgegeben. Diese Sonderausgabe von CoAst widmet sich der technischen Planung sowie dem wissenschaftlichen Hintergrund des ersten Österreichischen Satellitenpaares: UniBrite/BriteAustria. In den Konferenzbeiträgen zum First BRIght Target Explorer Workshop werden Fragen zum optimalen Satellitendesign, der Flugbahn, den Bodenstationen sowie Startmöglichkeiten erörtert. In weiterer Folge werden verschiede Klassen variabler Sterne als mögliche Zielobjekte und Beobachtungsstrategien für die photometrischen Beobachtungen besprochen. Contents: W. Weiss: BRITE-Constellation: Astrophysical Concept; O. Koudelka: BRITE-Austria/TUG Sat1: Project Overview; C. Grant and R. Zee: From MOST to BRITE: With a Stopover at CanX-2; M. Unterberger: BRITE-Austria/TUG Sat1: System Design and Simulation Results; R. Kuschnig: BRITE-Constellation: Science Operations Concept; A. Kaiser, S. Mochnacki and W. W. Weiss: BRITE-Constellation: Simulation of Photometric Performance; C. Lhotka and B. Funk: BRITE Orbits - Visiblity and Feature Plots; A. Kaiser and R. Kuschnig: BRITE-Constellation: Observation Planning; O. Koudelka: BRITE-Austria/TUG Sat1: Ground Station Technology; B. Josseck: BRITE-Austria/TUG Sat1: Launch Opportunities; D. Huber and P. Reegen: A MOST open-field data reduction sofware and its applications to BRITE; A. Kaiser, K. Zwintz and W. W. Weiss: BRITE-Constellation: Input Catalogue; M. Breger: The BRITE satellite and Delta Scuti Stars: The Magnificent Seven; T. Lüftinger and W. W. Weiss: CP Stars - probing stellar surface structure with BRITE Constellation; M. Gruberbauer, R. Neuteufel and W. W. Weiss: Observing Ƴ Doradus Stars with BRITE - an Outlook; K. Zwintz: β Pictoris: Planets and Pulsations; K. G. Strassmeier: Stellar Activity with BRITE: the "Aurigae" field; T. Kallinger: Exploring solar-type pulsation with BRITE; J. Daszyńska-Daszkiewicz: Identifying pulsation modes from two-passband photometry; E. A. Dorfi and A. Stökl: Theoretical Aspects of Massive Stars; G. Handler: β Cephei and Slowly Pulsating B stars as targets for BRITE-Constellation; R. Dvorak and Á. Bazsó: The search for extrasolar planets with BRITE; E. Paunzen: Cluster and Association Members; T. Lebzelter and J. Hron: BRITE stars on the AGB

Cosmological Evolution of Dwarf Galaxies: The Influence of Star Formation and the Multiphase Interstellar Medium

A model is developed to explain the cosmological evolution of dwarf galaxies. The population of small galaxies is found to evolve rapidly for z < 1, which provides a natural explanation for the evolution observed in the galaxy luminosity function. A tail is found in the redshift distribution of the faint blue excess that can extend to a redshift of 2. The star formation history is followed in detail for these objects. Constraints on the metallicity are identified for which stars are formed with much higher efficiency in a multiphase interstellar medium than in massive galaxies. Blue dwarf galaxies at the current epoch are identified with this starburst mode. The collapse of 1 and 2 σ perturbations of the initial density fluctuation spectrum is followed using the extended standard hierarchical clustering formalism. The collapse of these perturbations is normally associated with the formation of dwarf galaxies. These objects have shallow gravitational potential wells, and their evolution strongly depends upon the cooling time of the gas. The latter is determined by the ionization and chemical equilibrium of the gas in the presence of the intergalactic and local stellar radiation fields. The latter generally dominates and creates a feedback mechanism that regulates the evolutionary timescale. To improve upon previous models, essential new astrophysical ingredients are incorporated, such as a more detailed description of the physical processes regulating the multiphase structure of the interstellar medium in dwarf galaxies and the effects of evolution in the galaxy's metallicity on the formation of stars in molecular clouds. It is found that for a low star formation rate of 0.1 M☉ yr-1, the cooling time of interstellar gas is longer than the local Hubble time until z ~ 1. At this epoch, a two-phase medium makes the dwarf interstellar medium less fragile against supernova explosions, and the volume filling factor of the hot phase (107 K) becomes of order unity. The resulting X-ray luminosity is consistent with observations of nearby dwarf galaxies if exchange processes between the hot and cold phases of the interstellar medium (i.e., evaporation and ablation of clouds due the supernova blast wave) are included. The tenuous halo gas has a temperature in excess of the escape velocity and exhibits very high ionization stages. The dark matter halo potential (M/L ~ 102) influences the loss rate of metals and the star formation history. It is found that if the metallicity is between 0.01 and 0.1 Z☉ then a period of rapid star formation, ~1-3 M☉ yr-1, can be excited for z ~ 1. The physical reason for this starburst mode in our model is that the free-fall time exceeds the ambipolar diffusion timescale for clouds. Consequently, molecular clouds are not magnetically supported and star formation can proceed much more efficiently compared with more massive and metal-rich galaxies. Our results are consistent with the redshift distribution of dwarf galaxies observed in the Hubble Deep Field. In particular, a rapidly evolving dwarf population can account for the excess number counts of faint galaxies: the blue excess. Predictions are made for the color evolution of the old stellar population in these systems, observable with the Near-Infrared Camera and Multiobject Spectrometer (NICMOS) on the Hubble Space Telescope in the near future.

Population Synthesis Models

Increasingly complex population synthesis models have been developed during the last few years. Among the different authors working in the field, these groups have been particularly active: Arimoto &amp; Yoshii (1987), Guiderdoni &amp; Rocca-Volmerange (1987), Buzzoni (1989), Fritze-v. Alvensleben &amp; Gerhard (1994), Bressan, Chiosi, &amp; Fagotto (1994), Bruzual &amp; Chariot (1993, 1995). The basic astrophysical ingredients used in these models are the stellar evolutionary tracks and the stellar spectral libraries (either empirical or theoretical). The computational algorithms are different in each set of models, but, one way or the other, these models depend on the same adjustable parametric functions: (1) the stellar initial mass function (IMF); (2) the star formation rate (SFR); and (3) the rate of chemical enrichment (in some models Z = Z⊙ = constant). Most of the recent codes use the isochrone synthesis algorithm, which allows to compute the evolution of a simple stellar population (SSP), and from it, by a convolution integral, the properties of more complex composite stellar populations (CSP).