Munch: Monday, October 9, 2006

                               


 

    usual time and place:  12:30, 6th floor conference room

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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Munch Archive
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Star Formation in a Cosmological Simulation of Reionization

Authors: A. Gayler Harford, Nickolay Y. Gnedin
Comments: Submitted to ApJ. Comments are welcome
We study the luminosity functions of high-redshift galaxies in detailed hydrodynamic simulations of cosmic reionization, which are designed to reproduce the evolution of the Lyman-alpha forest between z=5 and z=6. We find that the luminosity functions and total stellar mass densities are in agreement with observations when plausible assumptions about reddenning at z=6 are made. Our simulations support the conclusion that stars alone reionized the universe.

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A Note on Cosmic (p,q,r) Strings

Authors: Mark G. Jackson
Comments: 4 pages
Report-no: FERMILAB-PUB-06-365-A
The spectrum of $(p,q)$ bound states of F- and D-strings has a distinctive square-root tension formula that is hoped to be a hallmark of fundamental cosmic strings. We point out that the BPS bound for vortices in ${\cal N}=2$ supersymmetric Abelian-Higgs models also takes the square-root form. In contrast to string theory, the most general supersymmetric field theoretic model allows for $(p,q,r)$ strings, with three classes of strings rather than two. Unfortunately, we find that there do not exist BPS solutions except in the trivial case. The issue of whether there exist non-BPS solutions which may closely resemble the square-root form is left as an open question.

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Separating the Weak Lensing and Kinetic SZ Effects from CMB Temperature Maps

Authors: Mario A. Riquelme, David N. Spergel
Comments: 13 pages, 1 figure
A new generation of CMB experiments will soon make sensitive high resolution maps of the microwave sky. At angular scales less than $\sim$10 arcminutes, most CMB anisotropies are generated at z $< 1000$, rather than at the surface of last scattering. Therefore, these maps potentially contain an enormous amount of information about the evolution of structure. Whereas spectral information can distinguish the thermal Sunyaev-Zeldovich (tSZ) effect from other anisotropies, the spectral form of anisotropies generated by the gravitational lensing and the kinetic Sunyaev-Zeldovich (kSZ) effects are identical. While spectrally identical, the statistical properties of these effects are different. We introduce a new real-space statistic, $<\theta (\hat{n})^3 \theta (\hat{m})>_c$, and show that it is identically zero for weakly lensed primary anisotropies and, therefore, allows a direct measurement of the kSZ effect. Measuring this statistic can offer a new tool for studing the reionization epoch. Models with the same optical depth, but different reionization histories, can differ by more than a factor of 3 in the amplitude of the kSZ-generated non-Gaussian signal.

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Ellipsoidal Universe Can Solve The CMB Quadrupole Problem

Authors: L. Campanelli, P. Cea, L. Tedesco
Comments: 4 pages, 2 figures, minor changes, reference added, to appear in Phys. Rev. Lett
The recent three-year WMAP data have confirmed the anomaly concerning the low quadrupole amplitude compared to the best-fit \Lambda CDM prediction. We show that, allowing the large-scale spatial geometry of our universe to be plane-symmetric with eccentricity at decoupling or order 10^{-2}, the quadrupole amplitude can be drastically reduced without affecting higher multipoles of the angular power spectrum of the temperature anisotropy.

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Searching for the first galaxies through gravitational lenses

Authors: D. Schaerer (1,2), R. Pello (2), J. Richard (2), E. Egami (3), A. Hempel (1), J.F. Le Borgne (2), J.-P. Kneib (4,5), M. Wise (6), F. Boone (7), F. Combes (7) ((1) Geneva Observatory, Sauverny, Switzerland, (2) Observatoire Midi-Pyrenees, Toulouse, France, (3) Steward Observatory, Tucson, USA, (4) OAMP, Marseille, France, (5) Caltech Astronomy, Pasadena, USA, (6) Astronomical Institute Anton Pannekoek, Amsterdam, The Netherlands, (7) Observatoire de Paris, Paris, France)
Comments: Comments: 4 pages, 4 colour figures, can also be downloaded via this http URL
Journal-ref: The Messenger 125 (2006), 20-23
Observing the first galaxies formed during the reionisation epoch, i.e. approximately within the first billion years after the Big Bang, remains one of the challenges of contemporary astrophysics. Several efforts are being undertaken to search for such remote objects. Combining the near-IR imaging power of the VLT and the natural effect of strong gravitational lensing our pilot program has allowed us to identify several galaxy candidates at redshift 6 <~ z <~ 10. The properties of these objects and the resulting constraints on the star formation rate density at high redshift are discussed. Finally we present the status of follow-up observations (ISAAC spectroscopy, HST and Spitzer imaging) and discuss future developments.

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DUNE: The Dark Universe Explorer

Authors: A. Refregier, O. Boulade, Y. Mellier, B. Milliard, R. Pain, J. Michaud, F. Safa, A. Amara, P. Astier, E. Barrelet, E. Bertin, S. Boulade, C. Cara, A. Claret, L. Georges, R. Grange, J. Guy, C. Koeck, L. Kroely, C. Magneville, N. Palanque-Delabrouille, N. Regnault, G. Smadja, C. Schimd, Z. Sun
Comments: 12 latex pages, including 7 figures and 2 tables. Procs. of SPIE symposium "Astronomical Telescopes and Instrumentation", Orlando, may 2006
Understanding the nature of Dark Matter and Dark Energy is one of the most pressing issues in cosmology and fundamental physics. The purpose of the DUNE (Dark UNiverse Explorer) mission is to study these two cosmological components with high precision, using a space-based weak lensing survey as its primary science driver. Weak lensing provides a measure of the distribution of dark matter in the universe and of the impact of dark energy on the growth of structures. DUNE will also include a complementary supernovae survey to measure the expansion history of the universe, thus giving independent additional constraints on dark energy. The baseline concept consists of a 1.2m telescope with a 0.5 square degree optical CCD camera. It is designed to be fast with reduced risks and costs, and to take advantage of the synergy between ground-based and space observations. Stringent requirements for weak lensing systematics were shown to be achievable with the baseline concept. This will allow DUNE to place strong constraints on cosmological parameters, including the equation of state parameter of the dark energy and its evolution from redshift 0 to 1. DUNE is the subject of an ongoing study led by the French Space Agency (CNES), and is being proposed for ESA's Cosmic Vision programme.

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The dark matter halos of massive, relaxed galaxy clusters observed with Chandra

Authors: R.W. Schmidt (1), S.W. Allen (2) ((1) ARI/Zentrum f. Astronomie Heidelberg, (2) KIPAC/Stanford)
Comments: 14 pages, 4 figures, 5 tables. Submitted to MNRAS
We use the Chandra X-ray Observatory to study the dark matter halos of 34 massive, dynamically relaxed galaxy clusters, spanning the redshift range 0.06<z<0.7. The observed dark matter and total mass (dark-plus-luminous matter) profiles can be approximated by the Navarro Frenk & White (hereafter NFW) model for cold dark matter (CDM) halos; for ~80 per cent of the clusters, the NFW model provides a statistically acceptable fit. In contrast, the singular isothermal sphere model can, in almost every case, be completely ruled out. We observe a well-defined mass-concentration relation for the clusters with a normalization and intrinsic scatter in good agreement with the predictions from simulations. The slope of the mass-concentration relation, c\propto M_vir^a/(1+z)^b with a=-0.41\pm0.11 at 95 per cent confidence, is steeper than the value a~-0.1 predicted by CDM simulations for lower mass halos. With the slope a included as a free fit parameter, the redshift evolution of the concentration parameter, b=0.54\pm0.47 at 95 per cent confidence, is also slower than, but marginally consistent with, the same simulations (b~1). Fixing a~-0.1 leads to an apparent evolution that is significantly slower, b=0.20\pm0.45, although the goodness of fit in this case is significantly worse. Using a generalized NFW model, we find the inner dark matter density slope, alpha, to be consistent with unity at 95 per cent confidence for the majority of clusters. Combining the results for all clusters for which the generalized NFW model provides a good description of the data, we measure alpha=0.88\pm0.29 at 95 per cent confidence, in agreement with CDM model predictions.

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Probing the nature of dark matter with Cosmic X-rays: Constraints from "Dark blobs" and grating spectra of galaxy clusters

Authors: Signe Riemer-Sorensen, Kristian Pedersen, Steen H. Hansen, Haakon Dahle
Comments: 4 pages, 4 figures
Gravitational lensing observations of galaxy clusters have identified dark matter ``blobs'' with remarkably low baryonic content. We use such a system to probe the particle nature of dark matter with X-ray observations. We also study high resolution X-ray grating spectra of a cluster of galaxies. From these grating spectra we improve the conservative constraints on a particular dark matter candidate, the sterile neutrino, by more than one order of magnitude. Based on these conservative constraints obtained from Cosmic X-ray observations alone, the low mass (m_s < 10keV) and low mixing angle (sin^2(2\theta) 10^{-6}) sterile neutrino is still a viable dark matter candidate.

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