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Bohringer H.,Max Planck Institute for Extraterrestrial Physics | Dolag K.,Max Planck Institute for Astrophysics | Dolag K.,Universitatssternwarte Munich | Chon G.,Max Planck Institute for Extraterrestrial Physics
Astronomy and Astrophysics | Year: 2012

Context: The largest uncertainty for cosmological studies using clusters of galaxies is introduced by our limited knowledge of the statistics of galaxy cluster structure and the related scaling relations between observables and cluster mass. A large effort has therefore been made to compile global galaxy cluster properties, in particular those obtained through X-ray observations, and to study their scaling relations. However, the scaling schemes used in the literature differ. Aims: The present paper aims to clarify this situation by providing a thorough review of the scaling laws within the standard model of large-scale structure growth and to discuss various steps in practical approximations. Methods: We derived the scaling laws for X-ray observables and cluster mass within the pure gravitational structure growth scenario. Using N-body simulations we tested the recent formation approximation used in earlier analytic approaches. It involves a redshiftdependent overdensity parameter. We find this approximation less precise than using a fiducial radius based on a fixed overdensity with respect to critical density. Results: Inspired by the comparison of the predicted scaling relations with observations, we propose a first-order modification of the scaling scheme to include the observed effects of hydrodynamics in structure formation. This modification involves a cluster-mass dependent gas-mass fraction. We also discuss the observational results of the reshift evolution of the most important scaling relations and find that a redshift dependence of the gas mass to total mass relation also has to be invoked within our modification scheme. Conclusions: We find that the current observational data are, within their uncertainties, consistent with the proposed modified scaling laws. © ESO 2012.

Montesano F.,Universitatssternwarte Munich | Montesano F.,Max Planck Institute for Extraterrestrial Physics | Sanchez A.G.,Max Planck Institute for Extraterrestrial Physics | Phleps S.,Max Planck Institute for Extraterrestrial Physics
Monthly Notices of the Royal Astronomical Society | Year: 2012

We obtain cosmological constraints from a measurement of the spherically averaged power spectrum of the distribution of about 90000 luminous red galaxies (LRGs) across 7646deg2 in the Northern Galactic Cap from the seventh data release (DR7) of the Sloan Digital Sky Survey. The errors and mode correlations are estimated thanks to the 160 LasDamas mock catalogues, created in order to simulate the same galaxies and to have the same selection as the data. We apply a model that can accurately describe the full shape of the power spectrum with the use of a small number of free parameters. Using the LRG power spectrum, in combination with the latest measurement of the temperature and polarization anisotropy in the cosmic microwave background (CMB), the luminosity-distance relation from the largest available Type 1a supernovae (SNIa) data set and a precise determination of the local Hubble parameter, we obtain cosmological constraints for five different parameter spaces. When all the four experiments are combined, the flat ΛCDM model is characterized by, Ωb= 0.045 ± 0.001, ns= 0.963 ± 0.011, σ8= 0.802 ± 0.021 and H0= 71.2 ± 1.4kms-1Mpc-1. When we consider curvature as a free parameter, we do not detect deviations from flatness: Ωk= (1.6 ± 5.4) × 10-3, when only CMB and the LRG power spectrum are used; the inclusion of the other two experiments does not improve this result substantially. We also test for possible deviations from the cosmological constant paradigm. Considering the dark energy equation of state parameter wDE as time independent, we measure, if the geometry is assumed to be flat, otherwise. When describing wDE through a simple linear function of the scale factor, our results do not evidence any time evolution. In the next few years new experiments will allow us to measure the clustering of galaxies with a precision much higher than achievable today. Models like the one used here will be a valuable tool in order to achieve the full potentials of the observations and obtain unbiased constraints on the cosmological parameters. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Dolag K.,Universitatssternwarte Munich | Dolag K.,Max Planck Institute for Astrophysics | Kachelriess M.,Norwegian University of Science and Technology | Ostapchenko S.,Norwegian University of Science and Technology | And 2 more authors.
Astrophysical Journal Letters | Year: 2011

High-energy photons from blazars can initiate electromagnetic pair cascades interacting with the extragalactic photon background. The charged component of such cascades is deflected and delayed by extragalactic magnetic fields (EGMFs), thereby reducing the observed point-like flux and potentially leading to multi-degree images in the GeV energy range. We calculate the fluence of 1ES 0229+200 as seen by Fe r m i-LAT for different EGMF profiles using a Monte Carlo simulation for the cascade development. The non-observation of 1ES 0229+200 by Fermi-LAT suggests that the EGMF fills at least 60% of space with fields stronger than O(10-16 to 10-15) G for lifetimes of TeV activity of O(102 to 104) yr. Thus, the (non-)observation of GeV extensions around TeV blazars probes the EGMF in voids and puts strong constraints on the origin of EGMFs: either EGMFs were generated in a space filling manner (e.g., primordially) or EGMFs produced locally (e.g., by galaxies) have to be efficiently transported to fill a significant volume fraction as, e.g., by galactic outflows. © 2011. The American Astronomical Society.

Najarro F.,CSIC - National Institute of Aerospace Technology | Hanson M.M.,University of Cincinnati | Puls J.,Universitatssternwarte Munich
Astronomy and Astrophysics | Year: 2011

Context. Mass-loss, occurring through radiation driven supersonic winds, is a key issue throughout the evolution of massive stars. Two outstanding problems are currently challenging the theory of radiation-driven winds: wind clumping and the weak-wind problem. Aims. We seek to obtain accurate mass-loss rates of OB stars at different evolutionary stages to constrain the impact of both problems in our current understanding of massive star winds. Methods. We perform a multi-wavelength quantitative analysis of a sample of ten Galactic OB-stars by means of the atmospheric code cmfgen, with special emphasis on the L-band window. A detailed investigation is carried out on the potential of Br α and Pfγ as mass-loss and clumping diagnostics. Results. For objects with dense winds, Brα samples the intermediate wind while Pfγ maps the inner one. In combination with other indicators (UV, Hα, Br γ) these lines enable us to constrain the wind clumping structure and to obtain "true" mass-loss rates. For objects with weak winds, Brα emerges as a reliable diagnostic tool to constrain Ṁ. The emission component at the line Doppler-core superimposed on the rather shallow Stark absorption wings reacts very sensitively to mass loss already at very low Ṁ values. On the other hand, the line wings display similar sensitivity to mass loss as Hα, the classical optical mass loss diagnostics. Conclusions. Our investigation reveals the great diagnostic potential of L-band spectroscopy to derive clumping properties and mass-loss rates of hot star winds. We are confident that Brα will become the primary diagnostic tool to measure very low mass-loss rates with unprecedented accuracy. © 2011 ESO.

Massey P.,Lowell Observatory | Neugent K.F.,Lowell Observatory | Hillier D.J.,University of Pittsburgh | Puls J.,Universitatssternwarte Munich
Astrophysical Journal | Year: 2013

The model atmosphere programs FASTWIND and CMFGEN are both elegantly designed to perform non-LTE analyses of the spectra of hot massive stars, and include sphericity and mass-loss. The two codes differ primarily in their approach toward line blanketing, with CMFGEN treating all of the lines in the co-moving frame and FASTWIND taking an approximate approach which speeds up execution times considerably. Although both have been extensively used to model the spectra of O-type stars, no studies have used the codes to independently model the same spectra of the same stars and compare the derived physical properties. We perform this task on 10 O-type stars in the Magellanic Clouds. For the late-type O supergiants, both CMFGEN and FASTWIND have trouble fitting some of the He I lines, and we discuss causes and cures. We find that there is no difference in the average effective temperatures found by the two codes for the stars in our sample, although the dispersion is large, due primarily to the various difficulties each code has with He I. The surface gravities determined using FASTWIND are systematically lower by 0.12 dex compared to CMFGEN, a result we attribute to the better treatment of electron scattering by CMFGEN. This has implications for the interpretation of the origin of the so-called mass discrepancy, as the masses derived by FASTWIND are on average lower than inferred from stellar evolutionary models, while those found by CMFGEN are in better agreement. © 2013. The American Astronomical Society. All rights reserved.

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