Munch: Monday, November 13, 2006

                               


 

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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


FAQ

What is Munch?
       Munch Archive

A limit on the presence of Earth-mass planets around a Sun-like star

Authors: Eric Agol (University of Washington) Jason H. Steffen (Fermilab)
Comments: Accepted for publication in MNRAS. 16 pages, 9 figures
Report-no: FERMILAB-PUB-06-279-A-CD
We present a combined analysis of all publicly available, visible HST observations of transits of the planet HD 209458b. We derive the times of transit, planet radius, inclination, period, and ephemeris. The transit times are then used to constrain the existence of secondary planets in the system. We show that planets near an Earth mass can be ruled out in low-order mean-motion resonance, while planets less than an Earth mass are ruled out in interior, 2:1 resonance. We also present a combined analysis of the transit times and 68 high precision radial velocity measurements of the system. These results are compared to theoretical predictions for the constraints that can be placed on secondary planets.

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How Tomographic Cosmic Shear Maps Lead to Constraints on Dark Energy Properties

Authors: Hu Zhan, Lloyd Knox (UC Davis)
Comments: 10 pages, 3 figures, submitted to PRD
Using a number of numerical tests and analytic arguments we investigate how measurements of cosmic shear lead to constraints on dark energy. We find that, in contrast to the case with galaxy number density correlation functions, standard rulers in the matter power spectrum play no significant role. Sensitivity to distance ratios is provided by the ratios in the lensing kernel. An absolute distance scale can only be established by breaking a potential degeneracy between growth and distance which can be done if the growth-redshift relation and distance-redshift relations are parameterized with sufficiently few parameters. For the quality of dark energy determination, growth determination is primarily important because it improves the distance reconstructions. The information about dark energy in the growth-redshift relation is always of secondary importance though the amount it contributes is highly dependent on what priors are taken in the cosmological parameter space. We also explain the dependence of dark energy constraints from cosmic shear, relative distance measures (supernovae) and absolute distance measures (baryon acoustic oscillations) on assumptions about the mean curvature.

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Improved Measurements of the CMB Power Spectrum with ACBAR

Authors: C.L. Kuo (1,2), P.A.R. Ade (3), J.J. Bock (1,2), J.R. Bond (4), C.R. Contaldi (4,5), M.D. Daub (6), J.H. Goldstein (7), W.L. Holzapfel (6), A.E. Lange (1,2), M. Lueker (6), M. Newcomb (8), J.B. Peterson (9), C. Reichardt (1), J. Ruhl (7), M.C. Runyan (10), Z. Staniszweski (7), ((1) Caltech, (2) JPL, (3) Cardiff, (4) CITA, (5) Imperial, (6) Berkeley, (7) CWRU, (8) Yerkes, (9) CMU, (10) Chicago)
Comments: 19 pages, 9 figures, ApJ
We report improved measurements of temperature anisotropies in the cosmic microwave background (CMB) radiation made with the Arcminute Cosmology Bolometer Array Receiver (ACBAR). In this paper, we use a new analysis technique and include 30% more data from the 2001 and 2002 observing seasons than the first release to derive a new set of band-power measurements with significantly smaller uncertainties. The planet-based calibration used previously has been replaced by comparing the flux of RCW38 as measured by ACBAR and BOOMERANG to transfer the WMAP-based BOOMERANG calibration to ACBAR. The resulting power spectrum is consistent with the theoretical predictions for a spatially flat, dark energy dominated LCDM cosmology including the effects of gravitational lensing. Despite the exponential damping on small angular scales, the primary CMB fluctuations are detected with a signal-to-noise ratio of greater than 4 up to multipoles of l=2000. This increase in the precision of the fine-scale CMB power spectrum leads to only a modest decrease in the uncertainties on the parameters of the standard cosmological model. At high angular resolution, secondary anisotropies are predicted to be a significant contribution to the measured anisotropy. A joint analysis of the ACBAR results at 150 GHz and the CBI results at 30 GHz in the multipole range 2000 < l < 3000 shows that the power, reported by CBI in excess of the predicted primary anisotropy, has a frequency spectrum consistent with the thermal Sunyaev-Zel'dovich effect and inconsistent with primary CMB. The results reported here are derived from a subset of the total ACBAR data set; the final ACBAR power spectrum at 150 GHz will include 3.7 times more effective integration time and 6.5 times more sky coverage than is used here.

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Dynamics of Linear Perturbations in f(R) Gravity

Authors: Rachel Bean, David Bernat, Levon Pogosian, Alessandra Silvestri, Mark Trodden
Comments: 15 pages, 4 figures
We consider predictions for structure formation from modifications to general relativity in which the Einstein-Hilbert action is replaced by a general function of the Ricci scalar. We work without fixing a gauge, as well as in explicit popular coordinate choices, and present the framework in a comprehensive and practical form that can be directly compared to standard perturbation analyses, appropriate for the modification of existing cosmological codes.
By considering the full evolution equations, we resolve perceived instabilities previously suggested, and instead find a suppression of perturbations. This result presents significant challenges for agreement with current cosmological structure formation observations.
The findings apply to a broad range of forms of f(R) for which the modification becomes important at low curvatures, disfavoring them in comparison with the LCDM scenario. As such, these results provide a powerful method to rule out a wide class of modified gravity models aimed at providing an alternative explanation to the dark energy problem.

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Statistical analysis of galaxy surveys - III: The non-linear clustering of red and blue galaxies in the 2dFGRS

Authors: Darren J. Croton, Peder Norberg, Enrique Gaztanaga, Carlton M. Baugh
Comments: 10 pages, 4 figures, submitted to MNRAS
We present measurements of the higher-order clustering of red and blue galaxies as a function of scale and luminosity made from the two-degree field galaxy redshift survey (2dFGRS). We use a counts-in-cells analysis to estimate the volume averaged correlation functions, xi_p, as a function of scale up to order p=5, and also the reduced void probability function. Hierarchical amplitudes are constructed using the estimates of the correlation functions: S_p=(xi_p/xi_2)^(p-1). We find that: 1) Red galaxies display stronger clustering than blue galaxies at all orders measured. 2) Red galaxies show values of S_p that are strongly dependent on luminosity, whereas blue galaxies show no segregation in S_p within the errors; this is remarkable given the segregation in the variance. 3) The linear relative bias shows the opposite trend to the hierarchical amplitudes, with little segregation for the red sequence and some segregation for the blue. 4) Faint red galaxies deviate significantly from the "universal" negative binomial reduced void probabilities followed by all other galaxy populations. Our results show that the characteristic colour of a galaxy population reveals a unique signature in its spatial distribution, and we discuss how this can provide new constraints for models of galaxy formation. Such constraints will hopefully further elucidate the physics responsible for shaping the cosmological evolution of galaxies.

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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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Modeling Chandra X-ray observations of Galaxy Clusters using Cosmological Simulations

Authors: Daisuke Nagai (1), Andrey V. Kravtsov (2), Alexey Vikhlinin (3,4) ((1) Caltech, (2) KICP, U.Chicago, (3) SAO, Harvard, (4) IKI, Moscow)
Comments: 6 pages, 4 figures. To appear in the Proceedings of "Heating vs. Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching (Germany)
X-ray observations of galaxy clusters potentially provide powerful cosmological probes if systematics due to our incomplete knowledge of the intracluster medium (ICM) physics are understood and controlled. In this paper, we study the effects of galaxy formation on the properties of the ICM and X-ray observable-mass relations using high-resolution self-consistent cosmological simulations of galaxy clusters and comparing their results with recent Chandra X-ray observations. We show that despite complexities of their formation and uncertainties in their modeling, clusters of galaxies both in observations and numerical simulations are remarkably regular outside of their cores, which holds great promise for their use as cosmological probes.

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