Day 572

Thursday.  First JC of the year.

1401.1146
Is the universe simpler than LCDM?
Walker, Loeb

In the standard LCDM, vacuum energy and CDM explains the formation and evolution of cosmic structure against the backdrop of Hubble flow.  Apparent discrepancies with observations on small galactic scales, which LCDM attribute to complexity in the baryon physics of galaxy formation.  Yet galaxies exhibit structural scaling relations that evoke simplicity, presenting a clear target for formation models.  Use published data to examine the relationship between dynamical components of such relations.  Tracers of gravitational potentials dominated by DM show a correlation between orbital size R and velocity V that can be expressed most simply as a characteristic acceleration, a_DM~1 km^2/s^2/pc ~ 3e-9 cm/s^2 ~ 0.2c (G rho_v)^1/2.  It remains to be seen whether LCDM predicts such behavior.

1401.1151
An improved model of charge transfer inefficiency and correlation algorithm for the Hubble Space Telescope
Massey, Schrabback, Cordes, Marggraf, Israel, Miller, Hall, Cropper, Prod'homme, Niemi

CCDs can be damaged by high energy radiation.  Degraded images appear blurred because of CTI, which trails bright objects as the image is read out.  Possible to correct most of the trailing during post-processing, by moving flux back to where it belongs.  Compare several popular algorithms, quantifying the effect of their physical assumptions and tradeoffs between speed and accuracy. Combine their best elements to construct a more accurate model of damaged CCDs in HST's ACS/WFC, and update it using data up to early 2013.  Algorithm now corrects 98% of CTI trailing in science exposures, a substantial improvement over previous work.  Further progress will be fundamentally limited by the presence of read noise.  Read noise is added after charge transfer so it does not get trailed - but it is incorrectly untrained during post-processing.

1401.1768
The clustering of galaxies in the SDSS-III rayon oscillation spectroscopic survey: galaxy clustering measurements in the low redshift sample of data release 11
Tojeiro, Ross, … et al

Present the distance measurement to z=0.32 using the DR11.  313,780 galaxies of LOWZ sample over 7341 sq deg to compute D_V=1264pm24 (r_d/r_d,fid) - a sub 2% measurement - using the BAO feature measured in the galaxy 2pt correlation function and PS.  Compare results to those obtained in DR10.  Study observational systematics in the LOWZ sample and quantify potential effects due to photometric offsets between the northern and southern Galactic caps.  Find the sample to be robust to all systematic effects found to impact on the targeting of higher-redshift BOSS galaxies, and that the observed NS tensions can be explained by either limitations in photometric calibration or bay sample variance, and have no impact on the final results.  The measurement, combined with the BAO scape at z=0.57, is used in Anderson+2013 to constrain cosmological parameters.
1312.4948
A new light on 21 cm intensity fluctuations from the dark ages
Ali-Haïmoud, Meerburg, Yuan

Fluctuations of the 21 cm brightness temperature before the formation of the first stars hold the promise of becoming a high-precision cosmological probe in the future.  The growth of over densities is very well described by perturbation theory at that epoch and the signal can in principle be predicted to arbitrary accuracy for given cosmological parameters.  Recently, it has been pointed out that an important physical effect has been neglected: baryons that CDM have supersonic relative velocities after recombination.  This relative velocity suppresses the growth of matter fluctuations on scales k~10^1-3 Mpc^-1.  In addition, the amplitude of the small-scale PS is modulated on the large scales over which the relative velocity varies, corresponding to k~0.005-1 Mpc^-1.  In this paper, the effect of the relative velocity on 21cm brightness temperature fluctuations from z>=30 is computed.  Show that the 21 cm PS is affected on most scales.  On small scales, the signal is typically suppressed several tens of percent, except for extremely small scales (k>~2000 Mpc^-1) for which the fluctuations are boosted by resonant excitation of acoustic waves.  On large scales, 21 cm fluctuations are enhanced due to the NL dependence of the brightness temperature on the underlying gas density and temperature.  The enhancement of the 21 cm power spectrum is of a few percent at k~0.1 Mpc^-1 and up to tens of percent at k<~0.005 Mpc^-1, for standard LCDM cosmology.  In principle this effect allows to probe the small-scale matter PS not only through a measurement of small angular scales but also through its effect on large angular scales.

1312.4961
Cosmo++: an object-oriented C++ library for cosmology
Aslanyan

Full implementation of C++ object-oriented programming techniques of a numerical library for cosmology.  Unified interface for using most of the frequently used numerical method in cosmology.  Most features implemented in Cosmo++ itself; part of the functionality is implemented by linking to other publicly available libraries.  The most important features of the library are CMB anisotropy PS and transfer function calculations, likelihood calculations, parameter space sampling tools, sky map simulations, and mask apodization.  Cosmo++ also includes a few mathematical tools that are frequently used in numerical research in cosmology and beyond.  A few simple examples are included to help the user understand the key features.  The library has been fully tested; describe some f the important tests in this paper.  Cosmo++ publicly available at github.com/aslanyan/cosmopp.

1312.4963
Constraining the Lyman alpha escape fraction with far-infrared observations of Lyman alpha emitters
Wardlow et al

Consider a wide range of FIR SEDs to determine upper limits on the FIR luminosities and FIR-derived SFRs of the LAEs.  These SFRs are then combined with those inferred from the Lya and UV emission to determine lower limits on the LAEs Lya escape fraction.  For the Sd SED template, the inferred LAEs f_esc are >~ 30% (1sigma) at z=2.8, 3.1 and 4.5, which are all significantly higher than the global f_esc at these redshifts.  Thus, if the LAEs f_esc follows the global evolution, then they have warmer FIR SEDs than the Sd galaxy template.  The average and M82 SEDs produce lower limits on the LAE F_esc of ~10 to 20% (1sigma), all of which are slightly higher than the global evolution of f_esc but consistent with it at the 2-3 sigma level.

1312.4975
THe color distribution of galaxies at redshift five
Rogers, .. Grogin,… et al

Present the results of a study investigating the rest-frame UV spectral slopes of z~5 Lyman-break galaxies (LBGs).  Find a clear CMR at z~5, such that the rest-frame UV slopes (beta) of brighter galaxies are notably redder than their fainter counterparts.  Determination of the z~5 CMR is well described by a linear relationship, with no clear evidence for a change in CMR slope at faint magnitudes (Muv>-18.9).  Using the results of detailed simulations, able to recover the intrinsic (i.e., free from noise) variation of galaxy colors around the CMR at z~5.  Find significant (12 sigma) evidence for intrinsic color variation in the sample as a whole.  Results also demonstrate that the width of the intrinsic UV slope distribution of z~5 galaxies increases from Delta(beta)=0.1 at Muv=-18 to Delta(beta)=0.4 at Muv=-21.  Suggest that the increasing width of the intrinsic galaxy color distribution and the CMR itself are both plausibly explained by a luminosity independent lower limit of beta=-2.1, combined with an increase in the fraction of red galaxies with increasing UV luminosity.

1312.4996
SDSS-III baryon oscillation spectroscopic survey: analysis of potential systematics in fitting of braying acoustic feature
Magaña, Ho, Xu, Sánchez, O'Connell, Eisenstein, Cuesta, Percival, Ross, et al
BAO to percent level accuracy is challenging, demands an understanding of many potential systematic to an accuracy well below 1%, in order to ensure that they do not combine significantly when compared to the statistical error.  DR11 reaches 1% statistical error, and this prompts an extensive search for all possible sub-percent level systematic errors, previously safe to ignore.  Analyze potential systematics in BAO fitting methodology using mocks and data from DR10 and 11.  Demonstrate the robustness of the fiducial multipole fitting methodology to be at 0.1-0.2% level with a wide range of tests in mock galaxy catalogs pre- and post-reconstruction.  Also find the DR10 and 11 data from BOSS to be robust against changes in methodology at similar level.  This systematic error budget is incorporated  into the error budget of BOSS DR10 and 11.  Of the wide range of changes investigated, find that when fitting pre-reconstructed data or mocks, the following changes have the largest effect on the best fit values of distance measurements both parallel and perpendicular to the LoS: (a) changes in NL correlation function template, (b) measurements both parallel and perpendicular to the LoS, (c) changes to the NL damping model parameters.  The priors applied do not matter in the estimates of the fitted errors as long as restricted to physically meaningful fitting regions.

1312.5154
Using correlations between CMB lensing and large-scale structure to measure primordial non-Gaussianity
Giannantonio, Percival

Use cross-correlation between galaxy surveys and CMB lensing signal to measure galaxy bias on very large scales, where local-type primordial non-G predicts a k^2 divergence.  Use CMB lensing map recently published by Planck, and measure its external correlations with a suite of six galaxy catalogues spanning a broad redshift range.  Consistently combine correlation functions to extend the recent analysis by Giannantonio+2013, where the density-desnity and the density-CMB temperature correlations were used.  Intrinsic noise of Planck lensing map affects the largest scales more severely; constraints on the galaxy bias are similar to the constraints from density-DMB temperature correlations.  Including lensing constraints only improves constraints marginally; obtain f_NL=12pm21 (1 sigma) from the combined data set.  However, the lensing measurements serve as an excellent test of systematic errors; now have 3 methods to measure the large-scale, scale-dependent bias from a galaxy survey: auto-correlation, and X-correlation with both CMB temperature and lensing.  As the publicly available Planck lensing maps have had their largest-scale modes at large multipoles (l<10) removed, which are the most sensitive to the scale-dependent bias, consider mock CMB lensing data covering all multipoles.  Find that, while the effect of f_NL indeed increases significantly on the largest scales, so do the contributions of both cosmic variance and they intrinsic lensing noise, so that the improvement is small.