Day 663

Friday.

1405.5527
MITEoR: a scalable interferometer for precision 21 cm cosmology
Zheng, Tegmark, et al

MIT Epoch of Reionization: a pathfinder low-frequency radio interferometer whose goal is to test technologies that improve the calibration precision and reduce the cost of high-sensitivity 3d mapping.  MITEoR accomplishes this by using massive baseline redundancy, which enables both automated precision calibration and correlator cost reduction.  For an N antenna instrument, the cost scaling is reduced from N^2 to NlogN.  Demonstrate and quantify the power and robustness of redundancy for scalability and precision.  Find that the calibration parameters precisely describe the effect of the instrument upon the measurements, allowing to form a model that is consistent with chi^2 per DoF<1.2 for as much as 80% of the observations.  Use results to develop an optimal estimator of calibration parameters using Wiener filtering, and explore the question of how often and how finely in frequency visibilities must be reliably measured to solve for calibration coefficients.  The success of MITEoR with its 64 dual-polarization elements bodes well for the more ambitious Hydrogen Eopch of Reionization Array (HERA) project and other next-generation instruments, which would incorporate many identical or similar technologies using hundreds more antennas, each with dramatically larger collecting area.

1405.5833
Solar system objects as cosmic rays detectors
Privitera, Motloch

In a recent Letter, Jupiter is presented as an efficient detector for UHECRs, through measurement by an Earth-orbiting satellite of gamma rays from UHECRs showers produced in Jupiter's atmosphere  Show that this result is incorrect, due to erroneous assumptions on the angular distribution of shower particles.  Evaluated other Solar System objects as potential targets for UHECRs detections, and found that the proposed technique is either not viable or not competitive with traditional ground-based UHECRs detectors.

1405.5836
The morphology of galaxies with quiescent recent assembly history in Lambda-CDM universe
Pedrosa et al

Standard disc formation scenario: discs form as the gas cools and flows into the center of the DM halo, conserving the specific angular momentum.  Major mergers have been shown to be able to destroy or highly perturb the disc components.  More recently, the alignment of the material that is accreted to form the galaxy has been pointed out as a key ingredient to determine galaxy morphology.  However, in a hierarchical scenario galaxy formation is a complex process which combiners these processes, and others, in a non-linear way so that the origin of galaxy morphology remains to be fully understood.  Aim at exploring the differences in the formation histories of galaxies with a variety of morphology but quite recent merger histories to identify which mechanisms are playing a major role.  Analyze when minor mergers could be considered relevant to determine galaxy morphology.  Also study the specific angular momentum content of the disc and central spheroidal components, separately.  Use cosmological hydrodynamical simulations that include an effective, physically-motivated SN feedback which is able to regulate the SF in hales of different masses.  Analyze the morphology and formation history of a sample of 15 galaxies of a cosmological simulation.  Perform a spheroid-disc decomposition of the selected galaxies and their progenitor systems.  The angular momentum orientation of the merging systems as well as their relative masses are estimated to analyze the role played by orientation and by minor mergers in the determination of the morphology.  Find the discs to be formed by conserving the specific angular momentum in accordance with the classical disk formation model.  The specific angular momentum of the stellar central spheroid correlates with the DM halo angular momentum determining a power law. 

1405.5857
A joint analysis of Planck and BICEP2 B modes including dust polarization uncertainty
Mortonson, Seljak

Analyze BICEP2 and Planck data using a model that includes CMB lensing, gravity waves, and polarized dust.  Recently published Planck dust polarization maps have highlighted the difficulty of estimating the amount of dust polarization in low intensity regions, suggesting that the polarization fractions have considerable uncertainties and may be significantly higher than previous predictions.  In this paper, do not assume anything about the dust polarization, except for the power spectrum shape, which is taken to be C^{BB,dust}_ell \propto ell^{-2.3}.  The resulting joint BICEP2+Planck analysis favors solutions without gravity waves, and the upper limit on the tensor-to-scalar ratio is r<0.11, a slight improvement relative to the Planck analysis alone which gives r<0.13 (95% CL).  The estimated amplitude of the dust polarization PS is in rough agreement with expectations for this field based on HI column density.  Address the cross-correlation analysis of BICEP2 at 150 GHz with BICEP1 at 100 GHz as a test of FG contamination.  Find that the null hypothesis of dust and lensing with r=0 gives Delta chi^2<2 relative to the hypothesis of no dust, so the frequency analysis does not strongly favor either model over the other.  Also discuss how Planck dust polarization maps may improve constraints.  If the dust polarization is measured perfectly, the limit can reach r<0.05 (or the corresponding detection significance if the observed dust signal plus the expected lensing signal is below the BICEP2 observations), but this degrades quickly to almost no improvement if the dust calibration error is 20% larger or if the Planck dust maps are not processed through the BICEP2 pipeline, including sampling variance noise.