1412.3110
Vast planes of satellites in a high resolution simulation of the Local Group: comparison to Andromeda
GIllet, et al
Search for vast planes of satellites (VPoS) in a high res sim of the LG, which improves significantly the resolution of former similar studies. Use a simple method for detecting planar configurations of satellites, and validate it on the known plane of M31. Implement a range of prescriptions for modeling the satellite populations, roughly reproducing the variety of recipes used in the literature, and investigate the occurrence and properties of planar structures in these populations. The structure of the simulated satellite systems is strongly non-random and contains planes of satellites, predominantly co-rotating, with, in some cases, sizes comparable to the plane observed in M31. However, the latter is slightly richer in satellites, slightly thinner and has stronger co-rotation, which makes it stand out as overall more exceptional than the simulated planes, when compared to a random population. Although the simulated planes that are found are generally dominated by one real structure, forming its backbone, they are also partly fortuitous and are thus not kinematically coherent structures as a whole. Provided that the simulated and observed planes of satellites are indeed of the same nature, the results suggest that the VPoS of M31 is not a coherent disc and that one third to 1/2 of its satellites must have larger proper motions perpendicular to the plane.
1412.3171
Intergalactic magnetic field spectra from diffuse gamma rays
Chen, et al
Non-vanishing parity-odd correlators of gamma ray arrival directions observed by Fermi-LAT indicate the existence of a helical intergalactic B-field. Successfully test this hypothesis using more stringent cuts of the data, Monte Carlo simulations with Fermi-LAT time exposure information, separate analyses for the northern and southern galactic hemispheres, and confirm predictions made in Tashiro&Vachaspati (2014). With some further technical assumptions, show how to reconstruct the magnetic helicity spectrum from the parity-odd correlations.
1412.3304
Sample of distant rich galaxy clusters in the ROSAT all sky survey
Buddendiek, Schrabback, ... et al
Finding a sample of the most massive clusters with z>0.6 can provide an interesting consistency check of the LCDM model. Present results from the search for clusters with 0.6<z<1.0 where the initial candidates were selected by cross-correlating the RASS faint and bright source catalogs with red galaxies from SDSS DR8. Survey thus covers 10k sq deg, much larger than previous studies. Deeper follow-up observations in 3 bands using the William Herschel Telescope and the LBT were performed to confirm the candidates, resulting in a sample of 44 clusters for which richness and red sequence redshifts are presented, as well as spectroscopic z for a subset. At least two of the cluster in the sample are comparable in richness to RCS2-J232727.7-020437, one of the richest systems discovered to date. Also obtained new observations with CARMA for a subsample of 21 clusters. For 11 of those, detect the SZ signature. The SZ signal allows to estimate M200 and check for tension with the cosmological standard model. Find no tension between cluster masses and the LCDM model.
1412.3451
galpy: a python library for galactic dynamics
Bovy
Describe the design, implementation, and usage of galpy a Python package for galactic-dynamics calculations. At its core, galpy consists of a general framework for representing galactic potentials both in Python an in C (for accelerated computations); galpy functions, objects, and methods can generally take arbitrary combinations of these as arguments. Numerical orbit integration is supported with a variety of Runge-Kutta-type and symplectic integrators. For planar orbits, integration on the phase-space volume is also possible. galpy supports the calculation of action-angle coordinates and orbital frequencies for a given phase-space point for general spherical potentials, using state-of-the-art numerical approximations for axisymmetric potentials, and making use of a recent general approximation for any static potential. A number of different distribution functions (DFs) are also included in the current release; currently these consist of 2d axisymmetric and non-axisymmetric disk DFs, a 3d disk DF, and a DF framework for tidal streams. Provide several examples to illustrate the use of the code. Present a simple model for the MW's gravitational potential consistent with the latest observations. Also numerically calculate the Oort functions for different tracer populations of stars and compare it to a new analytical approximation. Additionally, characterize the response of a kinematically-warm disk to an elliptical m=2 perturbation in detail. Overall, galpy consists of about 54k lines, including 23k lines of code in the model, 11k lines of test code, and about 20k lines of documentation. The test suite covers 99.6% of the code. galpy is available at github.com/jobovy/galpy with extensive documentation at galpy.readthedocs.org.
1412.3464
Lensing time delays as a substructure constraint: a case study with the cluster SDSS~J1004+4112
Mohammed, Saha, Liesenborgs
Gravitational lensing time delays are well known to depend on cosmo params, but they also depend on the details of the mass distribution of the lens. It is usual to model the mass distribution and use time-delay observations to infer cosmological parameters, but it is naturally also possible to take the cosmological parameters as given and use time delays as constraints on the mass distribution. This paper develops a method to isolate what exactly those constraints are, using a principal-components analysis of ensembles of free-form mass models. Find that time delays provide tighter constraints on the distribution of matter in the very high dense regions of the lensing clusters. Apply it to the cluster lens SDSS J1004+4112, whose rich lensing data includes two time delays. Find, assuming a concordance cosmology, that the time delays constrain the central region of the cluster to be rounder and less lopsided than would be allowed by lensed images alone. This detailed information about the distribution of the matter is very useful for studying the dense regions of the galaxy cluster which are very difficult to study with direct measurements. A further time-delay measurement, which is expected, will make this system more interesting.
1412.3683
Cosmological constraints from weak lensing peak statistics with CFHT Stripe-82 survey
Liu, ... Kneib, Leauthaud, Van Waerbeke, ... et al
Derive constraints on cosmo params using WL peak statistics measured on the ~130 sq deg of DS82. This analysis, based on a fast GPU code, demonstrates the feasibility of using peak statistics in cosmo studies. For the measurements, consider peak with S/N ratio in the range [3,6]. For a flat LCDM model with only Omega_m,sigma_8 as free parameters, constrained the parameters of the following relation sigma_8(Omega_m/0.27)^alpha = 0.82 pm 0.03 and alpha=0.43pm0.02. The alpha value found is considerably smaller than the one measured in 2pt and 3pt cosmic shear correlation analyses, showing a significant complementarity of peak statistics to standard WL cosmo studies. The derived constraints on Omega_m,sigma_8 are fully consistent with the ones form either WMAP9 or Planck. From the WL peak abundances alone, obtain marginalized mean values of Omega_m=0.38pm0.25 and sigma_8=0.81pm0.26. Finally, also explored the potential of using WL peak statistics to constrain the mass-concentration relation of DM haloes simultaneously with cosmo parameters.
1412.3703
Constraining the growth of perturbations with lensing of supernovae
Amendola, et al
A recently proposed technique allows one to constrain both the BG and perturbation cosmo params through the distribution function of supernova Ia apparent magnitudes. Extend this technique to alternative cosmo scenarios, in which the growth of structure does not follow the LCDM prescription. Apply the method first to the SN data provided with the JLA catalog combined with z distortion data and with low-z cluster data and show that although the SN alone are not very constraining, they help in reducing the confidence regions. Then apply method to future data from LSST and from a survey that approximates the Euclid satellite mission. In this case, show that the combined data are nicely complementary and can constrain the normalization sigma_8 and the growth rate index game to within 0.5% and 7%, respectively. In particular, the LSST SN catalog is forecast to give the constraint gamma(sigma_8/0.83)^6.7=0.55pm0.1. Also report on constraints relative to a step-wise parameterization of the growth rate of structures. These results show that SN lensing serves as a good cross-check on the measurement of perturbation parameters from more standard techniques.
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