Munch: Monday, November 6, 2006

                               


 

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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


FAQ

What is Munch?
       Munch Archive

Testing MOND with Local Group spiral galaxies

Authors: Edvige Corbelli, Paolo Salucci
Comments: 6 pages, 4 figures. To be published in MNRAS
The rotation curves and the relative mass distributions of the two nearby Local Group spiral galaxies, M31 and M33, show discrepancies with Modified Newtonian dynamic (MOND) predictions. In M33 the discrepancy lies in the kinematics of the outermost regions. It can be alleviated by adopting tilted ring models compatible with the 21-cm datacube but different from the one that best fits the data. In M31 MOND fails to fit the falling part of the rotation curve at intermediate radii, before the curve flattens out in the outermost regions. Newtonian dynamics in a framework of a stellar disc embedded in a dark halo can explain the complex rotation curve profiles of these two galaxies, while MOND has some difficulties. However, given the present uncertainties in the kinematics of these nearby galaxies, we cannot address the success or failure of MOND theory in a definite way. More sensitive and extended observations around the critical regions, suggested by MOND fits discussed in this paper, may lead to a definite conclusion.

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Can Astrophysical Gamma Ray Sources Mimic Dark Matter Annihilation in Galactic Satellites?

Authors: Edward A. Baltz, James E. Taylor, Lawrence L. Wai
Comments: 4 pages, 5 figures
Report-no: SLAC-PUB-12173
The nature of the cosmic dark matter is unknown. The most compelling hypothesis is that dark matter consists of weakly interacting massive particles (WIMPs) in the 100 GeV mass range. Such particles would annihilate in the galactic halo, producing high-energy gamma rays which might be detectable in gamma ray telescopes such as the GLAST satellite. We investigate the ability of GLAST to distinguish between the WIMP annihilation spectrum and the spectrum of known astrophysical source classes. Focusing on the emission from the galactic satellite halos predicted by the cold dark matter model, we find that the WIMP gamma-ray spectrum is unique; the separation from known source classes can be done in a convincing way. We discuss the follow-up of possible WIMP sources with Imaging Atmospheric Cerenkov Telescopes. Finally we discuss the impact that Large Hadron Collider data might have on the study of galactic dark matter.

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Sahar S. Allam, Douglas L. Tucker, Huan Lin, H. Thomas Diehl, James Annis, Joshua A. Frieman, E. Buckley-Geer 
TYPE: Scientific Paper in Journal based on Public SDSS Data
CATEGORY: SDSS-I
STATUS: To be submitteds to ApJ Letters in one week
PDF
Abstract:We report on the serendipitous discovery of the brightest Lyman Break 
Galaxy (LBG) currently known, a galaxy at z=2.73 that is being 
strongly lensed by the z=0.38 Luminous Red Galaxy (LRG) SDSS 
J002240.91+143110.4.  The arc of this gravitational lens system, 
which we have dubbed the ``8 o'clock arc'' due to its time of 
discovery, was initially identified in the imaging data of the 
Sloan Digital Sky Survey Data Release 4 (SDSS DR4); followup 
observations on the Astrophysical Research Consortium (ARC) 3.5m 
telescope at Apache Point Observatory confirmed the lensing nature 
of this system and led to the identification of the arc's spectrum as 
that of an LBG.  The arc has a spectrum and a redshift remarkably 
similar to those of the previous record-holder for brightest LBG 
(MS 1512-cB58, a.k.a ``cB58''), but, with an estimated total 
magnitude of (g,r,i) = (20.0,19.2,19.0) and surface brightness of 
(mu_g,mu_r, mu_i) = (23.3, 22.5, 22.3) mag/arcsec^2, 
the 8 o'clock arc is thrice as bright.  The 8 o'clock arc, which 
consists of three lensed images of the LBG, is 162deg (9.6 arcsec) 
long and has a length-to-width ratio of 6:1.  A fourth image of the 
LBG --- a counter-image --- can also be identified in the ARC 3.5m 
g-band images.  A simple lens model for the system assuming 
a singular isothermal ellipsoid potential yields an Einstein radius 
of theta_Ein=2.91 arcsec +/- 0.14 arcsec, a total mass for the 
lensing LRG (within the 10.6+/-0.5/h kpc enclosed by the lensed 
images) of 1.04*10^{12}/h M_sun, and a magnification factor for 
the LBG of 12.3(+15/-3.6).  The LBG itself is intrinsically quite 
luminous (approx. 6xL*) and shows indications of massive recent 
star formation, perhaps as high as 160/h M_sun/yr.

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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