1108.0056
Black holes of intermediate masses in globular clusters: constraints on a spin of a black hole
Buliga, Globina, Gnedin, Natsvlishvili, Piotrovich, Shaht
* Blandford-Znajek mechanism?
* Bondi-Hoyle mechanism (accretion rate)?
Determine values of spin of central black holes of intermediate massesin globular clusters. Determine spin: use known relation between the kinetic power of the relativistic jet and observable radio-luminosity of the region near the central black hole (Blandford-Znajek). Determine magnetic field strength: near even horizon of BH; derived via magnetic coupling mechanism. Determine accretion rate using Bondi-Hoyle.
* still not really sure what the important point of this paper is. Do they mean to constrain the BH spin from observable radio luminosities? Or is this theoretical (probably)?
1108.0175
Parity violation of gravitons in the CMB bispectrum
Shiraishi, Nitta, Yokoyama
* Weyl cubic terms?
Investigate bispectrum in CMB induced by non-Gaussianities due to gravitons. (Arises from parity-conserving and -violating Weyl cubic terms with time-dependent coupling. Consider time-dependent coupling; even in exact de Sitter spacetime, prity violation still appears in 3pt function of primordial gravitational waves, and could become large. The parity-conserving and -violating terms appear in completely different configurations of multipoles. Parity conserving appears in Sum_1^3 l_n = even, while parity violate appears in the sum being odd. (that's a potentially useful segregation). Shape of non-Gaussianity is similar to the equilateral one. Amplitudes of these spectra at large scale are roughly estimated as |b_lll} ~ l^{-4} x 4 x 1e-15 for Lambda = 1e6 and r = 0.1, where Lambda is an energy scale which sets the magnitude of the Weyl cubic terms (higher derivative corrections) and r is the scalar-to-tensor ratio.
* so there is the parity-violating term in the CMB bispectra from non-Gaussian\
ity of primordial gravitational waves.
* why would it violate parity?
1001.2333
Shape measurement biases from underfitting and ellipticity gradients
Bernstein
Precision WL requires <0.1% accuracy. Investigate measurement biases that are common to methods that rely on fitting elliptical isophote galaxy models to observed data. (1) First bias: true galaxy shapes do not match the models being fit---"underfitting bias". This bias is due to the method's attemt to use information at high spatial frequencies that has been destroyed by the convolution with the PSF and/or sampling. Solution: measure shapes that is explicitly confined to observable regions of k-space. (2) Second bias: ellipticity varies with radius---"ellipticity gradient bias." Any shape-measurement method is prone to this. With the new shape-measurement method, this bias can be reduced by factors of x20 to x100. Resulting shear estimator has multiplicative errors <.1% for high S/N images, even for highly asymmetric galaxies. Without training or calibration, the new method obtains Q=3000 in the GREAT08 challenge of blind shear reconstruction on low-noise galaxies, several times better than any previous method.
* the key is to not use the shape information from the invalid (i.e., destroyed) high-frequency region.
0905.4801
Limitations of model fitting methods for lensing shear estimation
Voigt, Bridle
Demonstrate a fundamental limit to the accuracy achievable by model-fitting techniques for shape measurements, if models are too simple. Wrong radial profile will bias the shape measurement even if the original galaxy has elliptical isophotes. Giving flexibility in the radial profile yields good shape measurements. But, that's not the case when bulge and disk of different ellipticities are overlapped. The limiting accuracy is dependent on the galaxy shape, but the most significant biases are from simple spiral-like galaxies. Implications for a given cosmic shear will depend on the actual distribution of the galaxies in the survey, PSF, selection function. Impact on cosmic shear results from current and near future surveys are found to be negligible. Develop better method that are less sensitive to morphology; use priors on galaxy shapes learnt from deep surveys.
0906.5092
Limitations for shapelet-based weak-lensing measurements
Melchior, Boehnert, Lombardi, Bartelmann
Shape estimators obtained from circular and elliptical shapelet models under two realistic conditions: (1) limited number of models available (shapelets), and (2) intrinsic galactic shapes not limited to shapelet models (Sersic profile). Additional conplications (PSF, pixelation and pixel noise) included. Steep and highly elliptical galaxy shapes cannot be accurately modeled within the circular shapelet basis system--they are biased towards shallower and less elongated shapes. Elliptical basis functions partially compensates, but for steep profiles, the results still rely on accurate elipticity priors (they have priors?). The result is that the bias is typically low in shear estimates. Bias can depend on the true intrinsic galaxy morphology, but also on the size and shape of the PSF. Need better shape measurement methods.
1108.0205
Galactic foreground contributions to the WMAP5 maps
Macellari, Pierpaoli, Dickenson, Vaillancourt
Cross-correlate intensity and polarization of WMAP5 data with template maps for synchrotron, dust and free-free (Bremsstrahlung) emission. Derive frequency dependence and polarization fraction for all three components in 48 different sky regions. The anomalous emission associated with dust is clearly detected over the ntire sky at 23 GHz and 33 GHz WMAP bands; is the dominant foreground at low Galactic latitude between b=-40 to +10. Synchrotron spectral index obtained from the K and Kz WMAP bands from an all-sky analysis is -3.32\pm0.12 for intensity and -3.01\pm0.03 for the polarized intensity (are these the expected value?). Polarization fraction is constant in frequency, but increases with latitude from 5% near the Galactic plane, up to ~40% in some regions at high latitude (why? only for synchrotron sources?), typically 10 to 20%. Anomalous dust and free-free emission appear to be relatively unpolarized (makes sense). Dust polarization is 3%. Compared to simulations, 8 regions show detected polarization above 2.5 sigma; one anomalous regions as 32% polarization. Dust polarization consistent with spinning dust emission, but polarized dust emission from magnetic-dipole radiation cannot be ruled out. Free-free emission was found to be unpolarized with an upper limit of 3.5% at 95% confidence.
* interesting overview of CMB foregrounds from galactic dust, synchrotron and free-free emission.
1108.0362
Propagation of ultrahigh energy nuclei in the magnetic field of our Galaxy
Giacinti, Kachelriess, Semikoz, Sigl
* EeV = exa (1e18) eV. kilo (3), mega (6), giga (9), tera (12), peta (15), exa (18), zetta (21)
Simulate propagation of UHE (ultra-high energy) heavy nuclei (how heavy?), with E>60 EeV in the Galactic magnetic field (GMF), both regular and turbulent. With UHE heavy nuclei, there is no one-to-one correspondence between the arrival direction of the CR at earth, and the direction of the extragalactic sources. Sources can have several distorted images on the sky. Compute images of galaxy clusters and of the supergalactic plane; show challenges and possibilities of UHECR astronomy with heavy nuclei (what possibilities?). Magnetic lensing effects from GMF. An 60 EeV Fe ion will not be detectable at earth due to magnetic lensing effects.
* supergalactic plane: a major structure in the local universe formed by preferential distribution of nearby galaxy clusters (Virgo cluster, Great Attractor, Pieces-Perseus super cluster).
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