1201.5374
How to detect gravitational waves through the cross-correlation of the galaxy distribution with the CMB polarization
Alizadeh, Hirata
CMB Thompson scatters off of reionization free electrons, inducing a correlation between the distribution of galaxies and the polarization pattern of the CMB, the magnitude of which is proportional to the quadrupole moment of radiation at the time of scattering. Since the quadrupole moment generated by gravitational waves (GWs) gives rise to a different polarization pattern than that produced by scalar modes, one can put constraints on the strength of GWs on large scales by cross-correlating the small scale galaxy distribution and CMB polarization. Use this method together with Fisher analysis to predict how well future surveys can measure the tensor-to-scalar ratio r. Find that with a future CMB experiment with detector noise Delta_P = 2 mu K-arcmin and a beam width theta_FWHM=2' and a future galaxy survey with limiting magnitude I < 25.6 one can measure the tensor-to-scalar ratio with an error sigma_r~0.09. To measure r~0.01, however, one needs 0.5muK-radian and theta_FWHM=1'. Also investigate a few systematic effects, non of which turn out to add any bias to the estimators, but increase the error bars by adding to the cosmic variance. The incomplete sky coverage has the most dramatic effect on the constraints for r on large sky cuts, with a reduction in signal-to-noise smaller than one would expect from the naive estimate (S/N)^2 propto f_sky. Specifically, find a degradation factor of f_deg=0.32 for a sky cut of |b| > 10 deg (f_sky=0.83) and f_deg = 0.05 for a sky cut of |b|>20 deg (f_sky=0.66). Nonetheless, given that the method has different systematics than the more conventional method of observing the large scale B modes directly, it may be used as an important check in the case of a detection.
1201.5375
A new window on primordial non-Gaussianity
Pajer, Zaldarriaga
Very little known about primordial curvature perturbations on scales smaller than about a Mpc. Measurements of the mu-type distortion of the CMB spectrum provide the unique opportunity to probe these scales over the unexplored range from 50 to 1e4 Mpc^-1. This is a very clean probe, in that it relies only on well-understood linear evolution. Point out that correlations between mu-distortion and temperature anisotropies can be used to test Gaussianity at these very small scales. In particular the mu-T cross correlation is proportional to the very squeezed limit of the primordial bispectrum and hence measures fNL^loc{ss}, while mu-mu is proportional to the primordial trispectrum and measures tauNL. Present a Fisher matrix forecast of the observational constraints.
* what is the mu-type distortion of the CMB spectrum? mu stands for chemical potential. talking about mu-distortion caused by Silk damping as the signal.
1201.5376
The chemical signature of relic star cluster in the Sextans Dwarf spheroidal galaxy-implications for near-field cosmology
Karlsson, Bland-Hawthorn, Freemen, Silk
Found a possibly dissolved star cluster of extremely poor metallicity of [Fe/H]=-2.7. In the future with large surveys, might be able to put firm constraints on the dwarf-galaxy origin of MW's stellar halo. Also argue that the average star cluster mass in the majority of the newly discovered ultra-faint dwarf galaxies was notably lower than it is in the Galaxy today and possibly lower than in the more luminous, classical dwarf spheroidal galaxies. Moreover, the slope of the cumulative metallicity function in dwarf spheroidals falls below that of the ultra-faints, which increases with increasing metallicity as predicted from the stochastic chemical evolution model. These two findings, together with a possible difference in the ratio suggest that the ultra-faint dwarf galaxy population, or a significant fraction thereof, and the dsph population, were formed in different environments and would thus be distinct in origin.
1201.5377
UV properties of galactic globular clusters with GALEX I. the color-magnitude diagrams
Schiavon, et al
Present GALEX data for 44 galactic globular clusters. Color-magnitude diagrams presented. Blue and intermediate-blue horizontal branch is the dominant feature of the UV color-magnitude diagrams of old Galactic globular clusters. Sample large enough to display the variaty of horizontal branch shapes found in old stellar populations. Other stellar types that are obviously detected are blue stragglers and post core-He burning stars. The main features of UV color-magnitude diagrams of Galactic globular clusters are briefly discussed. Establish the locus of post-core He burning stars n the UV color-magnitude diagram and present a catalog of candidate AGB-manque, post early-AGB, and post-AGB stars within the cluster sample.
No comments:
Post a Comment