Day 1306

Tuesday.  Wednesday.

1709.03491

The Breakthrough Listen Search for Intelligent Life: 1.1-1.9 GHz observations of 692 nearby stars

Enriquez, et al

Report on a search for engineered signals from a sample of 692 nearby stars using the Green Bank Telescope (GBT), undertaken as part of the Breakthrough Listen Initiative search for extraterrestrial intelligence.  Observations were made over 1.1-1.9 GHz (L-band), with 3 sets of 5 minute observations of the 692 primary targets, interspersed with 5-minute observations of secondary targets.  By comparing the "on" and "off" observations, able to identify terrestrial interference and place limits on the presence of engineered signals from putative extraterrestrial civilizations inhabiting the environs of the target stars.  During the analysis, 11 events passed the thresholding algorithm, but detailed analysis of their properties indicates they are consistent with known examples of anthropogenic radio frequency interference.  Conclude that at the time of the observations none of the observed systems host high-duty-cycle radio transmitters emitting between 1.1 to 1.9 GHz with an EIRP of ~1e13W, which is readily achievable by our own civilization.  The results suggest that fewer than ~0.1% of the stellar systems within 50pc possess the type of transmitters searched in this survey.

1709.03499

Stochastic order redshift technique (SORT): a simple, efficient and robust method to improve cosmological redshift measurements

Tejos, Rodrigez-Puebla, Primack

The method is based on the presence of a reference sample for which a precise redshift number distribution (dN/dz) can be obtained for different pencil-beam-like sub-volumes within the original survey.  For each sub-volume impose: (i) that the redshift number distribution of the uncertain redshift measurements matches the reference dN/dz corrected by their selection functions; and (ii) the rank order in redshift of the original ensemble of uncertain measurements is preserved.  The latter step is motivated by the fact that random variables drawn from Gaussian probability density functions (PDFs) of different means and arbitrarily large standard deviations satisfy stochastic ordering.  Then repeat this simple algorithm for multiple arbitrary pencil-beam-like overlapping sub-volumes; in this manner, each uncertain measurement has multiple (non-independent) "recovered" redshifts which can be used to estimate a new redshift PDF.  Refer to this method as SORT.  Used a state-of-the-art N-body simulation to test the performance of SORT under simple assumptions and found that it can improve the quality of cosmological redshifts in an efficient and robust manner.  Particularly, SORT redshifts are able to recover the distinctive features of the 'cosmic web' and can provide unbiased measurement of the 2pt correlation function on scales > 4 Mpc/h.  Given its simplicity, envision that a method like SORT can be incorporated into more sophisticated algorithms aimed to exploit the full potential of large extragalactic photometric surveys.


1709.03542
The last 6 Gyr of dark matter assembly in massive galaxies from the Kilo Degree Survey
Tortora, et al

Study the DM assembly in the central regions of massive early-type galaxies up to z~0.65.  Use a sample of ~3800 massive log(M*/Msun)>11.2 galaxies with photometry and structural parameters from 156 sq deg of KiDS, and spectroscopic redshifts and velocity dispersions from SDSS.  Obtain central total-to-stellar mass ratios, Mdyn/M*, and DM fractions, by determining dynamical masses, Mdyn from Jeans modeling of SDSS aperture velocity dispersion and stellar masses, M*, from KiDS galaxy colors.  First show how the central DM fraction correlates with structural parameters, mass and density proxies, and demonstrate that most of the local correlations are still observed up to z~0.65; at fixed M*, local galaxies have larger DM fraction, on average, than their counterparts at larger redshift.  Also interpret these trends with a non universal IMF, finding a strong evolution with z, which contrast independent observations and is at odds with the effect of galaxy mergers.  For a fixed IMF, the galaxy assembly can be explained, realistically, by mass and size accretion, which can be physically achieved by a series of minor mergers.  Reproduce both the Re-M* and Mdyn/M* - M* evolution with stellar and dark mass changing at different rate.  This results suggests that the main progenitor galaxy is merging with less massive systems, characterized by a smaller Mdyn/M*, consistently with results from halo abundance matching.


1709.03599
Lens covariance effects on likelihood analyses of CMB power spectra
Motloch, Hu

Non-Gaussian correlations induced in CMB PS by gravitational lensing must be included n likelihood analyses for future CMB experiments.  Present a simple but accurate likelihood model which includes these correlations and use it for MCMC parameter estimation from simulated lensed CMB maps in the context of LCDM and extensions which include the sum of neutrino masses or the DE EoS w. If lensing-induced covariance is not taken into account for a CMB-S4 type experiment, the errors for one combination of parameters in each case would be underestimated by more than a factor of two and lower limits on w could be misestimated substantially.  The frequency of falsely ruling out the true model or finding tension with other data sets would also substantially increase.  The analysis also enables a separation of lens and unlicensed information from CMB PS, which provides for consistency tests of the model and, if combined with other such measurements, a nearly lens-sample-variance free test for systematics and new physics in the unlensed spectrum . This parameterization also leads to a simple effective likelihood that can be used to assist model building in case consistency tests of LCDM fail.