Thursday, 24. November 2011

SED fitting with MCMC: methodology and application to large galaxy surveys

Authors: Viviana Acquaviva, Eric Gawiser, Lucia Guaita

http://arxiv.org/abs/1111.4243v2

Abstract: We present GalMC (Acquaviva et al. 2011), our publicly available Markov Chain Monte Carlo algorithm for SED fitting, show the results obtained for a stacked sample of Lyman Alpha Emitting galaxies at z ~ 3, and discuss the dependence of the inferred SED parameters on the assumptions made in modeling the stellar populations. We also introduce SpeedyMC, a version of GalMC based on interpolation of pre-computed template libraries. While the flexibility and number of SED fitting parameters is reduced with respect to GalMC, the average running time decreases by a factor of 20,000, enabling SED fitting of each galaxy in about one second on a 2.2GHz MacBook Pro laptop, and making SpeedyMC the ideal instrument to analyze data from large photometric galaxy surveys.

Comments: An alternative to SEDfit?

Reconstruction of Gravitational Lensing Using WMAP 7-Year Data

Authors: Chang Feng, Brian Keating, Hans P. Paar, Oliver Zahn

http://arxiv.org/abs/1111.2371v1

Abstract: Gravitational lensing by large scale structure introduces non-Gaussianity into the Cosmic Microwave Background and imprints a new observable, which can be used as a cosmological probe. We apply a four-point estimator to the Wilkinson Microwave Anisotropy Probe (WMAP) 7-year coadded temperature maps alone to reconstruct the gravitational lensing signal. The Gaussian bias is simulated and subtracted, and the higher order bias is investigated. We measure a gravitational lensing signal with a statistical amplitude of $\mathcal {C}$ = $1.27\pm 0.98$ using all the correlations of the W- and V-band Differencing Assemblies (DAs). We therefore conclude that WMAP 7-year data alone, can not detect lensing.

Comments: The authors have applied an optimal quadratic estimator (W. Hu, Phys. Rev. D64,083005 (2001) and W. Hu, Astrophys. J. Lett. 557, 79 (2001)) to WMAP-7 temperature maps alone for the first time. They find evidence of lensing only at 1.30sigma.

Non-thermal Emissions from Cool Cores Heated by Cosmic-Rays in Galaxy Clusters

Authors: Yutaka Fujita, Yutaka Ohira

http://arxiv.org/abs/1111.4208

Abstract: We study non-thermal emissions from cool cores in galaxy clusters. We adopted a recent model, in which cosmic-rays (CRs) prevail in the cores and stably heat them through CR streaming. The non-thermal emissions come from the interaction between CR protons and intracluster medium (ICM). Comparison between the theoretical predictions and radio observations shows that the overall CR spectra must be steep, and most of the CRs in the cores are low-energy CRs. Assuming that the CRs are injected through AGN activities, we study the nature of the shocks that are responsible for the CR acceleration. The steep CR spectra are likely to reflect the fact that the shocks travel in hot ICM with fairly small Much numbers. We also study the dependence on the CR streaming velocity. The results indicate that synchrotron emissions from secondary electrons should be observed as radio mini-halos in the cores. In particular, low-frequency observations (e.g. LOFAR) are promising. On the other hand, the steepness of the spectra makes it difficult to detect non-thermal X-ray and gamma-ray emissions from the cores. The low-energy CRs may be heating optical filaments observed in the cores.

Comments: Cosmic Rays from AGN propagate via Alfven waves (at low Mach numbers) through the intracluster medium and heat it. The paper is well structured, the only problem is the collection of plots in the end, which makes reading a bit annoying.

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