Day 727

Thursday.

1408.2720
The strongest gravitational lenses: IV. The order statistics of the largest Einstein radii with cluster mergers
Redlich, Waizmann, Bartelmann

Investigate the impact of galaxy-cluster mergers on the order statistics of the largest Einstein radii.  Show that the inclusion of mergers significantly shifts the extreme value distribution of the largest Einstein radius to higher values, typically increasing the expected value by ~10%.  A comparison with current data reveals that the largest observed Einstein radius agrees excellently well with the theoretical predictions of LCDM model at z>0.5.  At z<0.5, the results are somewhat more controversial.  Although cluster mergers also increase the expected values of the order statistics of the largest Einstein radii by ~10%, the theoretically expected values are notably lower (~3 sigma deviation for n=12) than the largest Einstein radii of a selected sample of SDSS clusters in the redshift range 0.1<z<0.55.  The uncertainties of the observed Einstein radii are still large, however, and thus the measurements need to be carefully revised in future works.  Therefore, given the premature state of current observational data, there is still no reliable statistical evidence for observed Einstein radii to exceed the theoretical expectations of the standard cosmological model.

1408.2907
Sailing under the Magellanic clouds: A DECam view of the Carina Dwarf
McMonigal, et al

Present deep optical photometry from the DECam imager on the 4m Blanco telescope of 12 deg^2 of the Carina dwarf spheroidal.

1408.4451
Black holes at the centers of nearby dwarf galaxies
Moran, et al

Identify 28 AGNs nearby (d<80 Mpc) low mass, low luminosity dwarf galaxies.  The accreting objects at the galaxy centers are expected to be intermediate-mass black holes (IMBHs) with M_BH<1e6 Msun.  The AGNS were selected using several optical emission-line diagnostics after careful modeling of the continuum present in the spectra.  Limited the survey to objects with spectral characteristics similar to those of Seyfert nuclei, excluding emission-line galaxies with ambiguous spectra that could be powered by stellar processes.  The his galaxies in the sample are thus the least massive objects in the very local universe certain to contain central BHs.  Given the focus on the nearest objects included in the SDSS, the survey is more sensitive to low-luminosity emission than previous optical searches for AGNs in low-mass galaxies.  The [O III] lambda 5007 luminosities of the Seyfert nuclei in the sample have a median value of L_5007=2e5 Lsun and extend down to 1e4 Lsun.  Using published data for broad-line IMBH candidates, have derived an [O III] bolometric correction of log (L_bol/L_5007) = 3.0pm0.3, which is significantly lower than values obtained for high-luminosity AGNs.  Applying this correction to the sample, obtain minimum black-hole mass estimates that fall mainly in the 1e3 Msun-1e4 Msun range, which is roughly where the predicted mass functions for different BH seed formation scenarios overlap the most.  In the stellar mass range that includes the bulk of the AGN host galaxies in the sample, derive a lower limit on the AGN fraction of a few percent, indicating that active nuclei in dwarf galaxies are not as rare as previously thought.

1408.4648
The redshift-space galaxy two-point correlation function and baryon acoustic oscillations
Jeong, Dai, Kamionkowski, Szalay

Describe the anisotropies that arise in the z-space galaxy 2PCF and elucidate the origin of features that arise in the dependence of the BAOs on the angle between the orientation of the galaxy pair and the line of sight.  Do so with a derivation of the configuration-space 2PCF using streaming model.  Find that, contrary to common belief, the locations of BAO peaks in the redshift-space 2PCF are anisotropic even in the linear theory.  Aniosotropies in BAO depend strongly on the method of extracting the peak, showing maximum 3% angular variation.  Also find that extracting the BAO peak of r^2 xi(r,mu) significantly reduces the anisotropy to sub-percent level angular variation.  When subtracting the tilt due to the broadband behavior of the 2PCF, the BAO bump is enhanced along the line of sight because of local infall velocities toward the BAO bump.  Precise measurement of the angular dependence of the z-space 2PCF will allow new geometrical tests of DE beyond the BAO.

1408.4742
Cosmic discordance: Are Planck CMB and CHFTLenS weak lensing measurements out of tune?
MacCrann, Zuntz, Bridle, Jain, Becker

Examine the level of agreement between low-z WL data and the CMB using CFHTLenS and Planck+WMAP polarization.  Perform an independent analysis of the CFHTLenS six bin tomography results of Heymans+ 2013.  Extend their systematics treatment and find the cosmological constraints to be relatively robust to the choice of NL modeling, extension to the AI model and inclusion of baryons.  Find that the 90% confidence contours of CFHTLenS and Planck+WP do not overlap even in the full 6D parameter space of LCDM, so the two datasets are discrepant.  Allowing a massive active neutrino or tensor modes does not significantly resolve the disagreement in the full n-dimensional parameter space.  Results differ from some i the literature because of the use of the full tomographic information in the WL data and marginalize over systematics.  Note that adding a sterile neutrino to LCDM does bring the 8D 64% contours to overlap, mainly due to the extra effective number of neutrino species, which is found to be 0.84pm0.35 (68%) greater than standard on combining the datasets.  Discuss why this is not a completely satisfactory resolution, leaving open the possibility of other new physics or observational systematics as contributing factors.  Provide updated cosmology fitting functions for the CFHTLenS constraints and discuss the differences from ones used in the literature.

1408.4758
Reconciling Planck cluster counts and cosmology: Chandra/XMM instrumental calibration and hydrostatic mass bias
Israel, Schellenberger, Nevalainen, Massey, Reiprich

Temperature of X-ray emitting gas T_X is often used to infer the total mass of galaxy clusters (under the assumption of hydrostatic equilibrium).  Unfortunately, XMM-Newton and Chandra observatories measure inconsistent temperatures for the same gas, due to uncertain instrumental calibration.  Translate the relative bias in T_X measurements of Schellenberger+ 2014 into a bias on inferred mass for a sample of clusters with homogeneous WL masses, to simultaneously examine the hydrostatic bias and instrument calibration.  Israel+2014 found consistent WL and Chandra hydrostatic X-ray masses for a sample of clusters at z~0.5 and masses of a few 1e14 Msun . Find their XMM-Newton masses to be lower by b^xcal=15-20% than their Chandra masses.  At the massive end (>5e14 Msun), the XMM-Newton masses are~35% lower than the WL masses.  Assuming that the true hydrostatic bias is 20%, as indicated by simulations, results for the massive end indicate that Chandra's calibration of the energy dependence of the effective area is more accurate than XMM-Newtons's.  However, the opposite appears to be true at the low mass end.  In addition, follow through how a bias in the T_X would affect the Planck cluster counts.  X-ray masses feature prominently in the apparent discrepancy between Planck measurement of the CMB and the number of clusters detected via the SZ effect.  The SZ masses were indirectly calibrated via XMM-Newton observations.  Assuming the Chandra calibration to be correct, and amplified residual calibration bias (up to ~30% in mass) could ease the tension in the cosmological interpretation, while keeping the bias due to departures from hydrostatic equilibrium b^hyd~0.2, as expected from simulations.