Day 839

Tuesday.

1502.06001
Detection and localization of single-source gravitational waves with pulsar timing arrays
Zhu, et al

PTAs can be used to search for very low frequency (1e-9 to 1e-7 Hz) GWs.  Present a general method for the detection and localization of single-source GWs using PTAs.  Demonstrate the effectiveness of this new method for 3 types of signals: monochromatic waves as expected from individual SMBH binaries in circular orbits, GWs from eccentric binaries and GW bursts.  Also test its implementation in realistic data sets that include effects such as uneven sampling and heterogeneous data spans and measurement precision.  It is shown that the method, which works in the frequency domain, performs as well as published time-domain methods.  Find it equivalent to the P_e-statistic proposed in Ellis+2012 for monochromatic waves.  Also discuss the construction of null streams --- data streams that have null response to GWs and the prospect of using tunnel streams as a consistency check in the case of detected GW signals.  Finally, present sensitivities to individual SMBH binaries in eccentric orbits.  Find that a monochromatic search that is designed for circular binaries can efficiently detect eccentric binaries with both high and low eccentricities, while a harmonic summing technique provides greater sensitivities only for binaries with moderate eccentricities.


1502.06016
PAPER-64 constraints on reionization: the 21cm power spectrum at z=8.4
Ali, Parsons, ... Pober, Liu, Aguirre, et al

Report new limits on 21 cm emission from cosmic reionization based on a 135-day observing campaign with a 64-element deployment of the D.C.Backer Precision Array for probing the epoch of reionization (PAPER) in South Africa.  This work extends the Parsons+2014 with more collection area, a longer observing periods, improved redundancy-based calibration, optimal fringe-rate filtering, and improved power-spectral analysis using optical quadratic estimators.  The result is a new 2sigma upper limit on Delta^2(k) of (22.4 mK)^2 in the range 0.15<k<0.5 h/Mpc at z=8.4.  This represent a three-fold improvement over the previous best upper limit.  This upper limit supports and extends previous evidence against extremely cold reionization scenarios.  Conclude with a discussion of implications for future 21cm reionization experiments, including the newly funded Hydrogen Epoch of Reionization Array (HERA).


1502.06020
Cosmology and astrophysics from relaxed galaxy clusters I: sample selection
Mantz, Allen, Morris, Schmidt, von der Linden, Urban

First in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters.  Present a new, automated method for identifying relaxed clusters based on their morphologies in X-ray imaging data.  While broadly similar to others in the literature, the morphological quantities that are measured are specifically designed to provide a fair basis for comparison across a range of data quality and cluster redshifts, to be robust against missing data due to point-source masks and gaps between detectors, and to avoid strong assumptions about the cosmological background and cluster masses.  Based on 3 morphological indicators - Symmetry, Peakiness and Alignment - develop the SPA criterion for relaxation.  This analysis was applied to a large sample of cluster observations from the Chandra and ROSAT archives.  Of the 361 clusters which received the SPA treatment, 57 (16%) were subsequently found to be relaxed according to this criterion.  Compare measurements to similar estimators in the literature, as well as projected ellipticity and other image measures, and comment on trends in the relaxed cluster fraction with z, temperature, and survey selection method.  Code implementing the morphological analysis will be made available on the web.


1502.06456
The Atacama cosmology telescope: measuring radio galaxy bias through cross-correlation with lensing
Allison, ... Sherwin, ... Devlin, ... Hlozek, Jarvis, ... et al

Correlate the positions of radio galaxies in the FIRST survey with the CMB lensing convergence estimated from ACT over 470 sq deg to determine the bias of these galaxies.  Remove optically cross-matched sources below z=0.2 to preferentially select AGN.  Measure the angular cross-power spectrum C^{kappa g}_ell at 4.4 sigma significance in the multipole range 100<l<3000, corresponding to physical scales between 2-60Mpc at an effective z=1.5.  Modeling the AGN population with a z-dependent bias, the cross-spectrum is well fit by the Planck best-fit LCDM cosmological model.  Fixing the cosmology, fit for the overall bias model normalization, finding b(z_eff)=3.5pm0.8 for the full galaxy sample, and b(z_eff)=4.0pm1.1(3.0pm1.1) for source brighter (fainter) than 2.5 mJy.  This measurement characterizes the typical halo mass of radio-loud AGN: find log(M_halo/M_sun)=13.6pm0.3.