1507.05614
Statistical signatures of Panspermia in Exoplanet surveys
Lin, Loeb
A fundamental astrobiological question is whether life arose spontaneously on earth or was transported here from an extrasolar system. Propose a new strategy to answer this question based on the principle that life which arose via spreading will exhibit more clustering than life which arose spontaneously. Develop simple statistical models of panspermia to illustrate observable consequences of these excess correlations. Future searches for biosignatures in the atmospheres of exoplanets could test these predictions: panspermia predicts large regions in the MW where life saturates its environment interspersed with voids where life is very uncommon. In a favorable scenario, detection of as few as ~25 biologically active exoplanets could yield a 5 sigma detection of panspermia.
1507.05618
Antisymmetric galaxy cross-correlations as a cosmological probe
Dai, Kamionkowski, et al
The auto-correlation between two members of a galaxy population is symmetric under the interchange of the 2 galaxies being correlated. The cross-correlation between two different types of galaxies, separated by a vector r, is not necessarily the same as that for a pair separated by -r. Local anisotropies in the 2pt x-correlation function may thus indicate a specific direction which when mapped as a function of position trace out a vector field. This vector field can then be decomposed into longitudinal and transverse components, and those transverse components written as positive- and negative-helicity components. A locally asymmetric x-correlation of the longitudinal type arises naturally in halo clustering, even with Gaussian ICs, and could be enhanced with local-type non-Gaussianity. Early-Universe scenarios that introduce a vector field may also give rise to such effects. These antisymmetric cross-correlations also provide a new possibility to seek a preferred cosmic direction correlated with the hemispherical power asymmetry in the cosmic microwave background and to seek a preferred location associated with the CMB cold spot. New ways to seek cosmic parity breaking are also possible.
1507.05627
The universality of the viral halo mass function and models for non-universality of other halo definitions
Despali, Giocoli, Angulo, Tormen, Sheth, Baso, Moscardini
The abundance of galaxy clusters can constrain both the geometry and structure growth in the Universe. However, this probe could be significantly complicated by recent claims of non universality -- non-trivial dependencies with respect to the cosmological model and redshift. In this work, analyse the dependence of the mass function on the way haloes are identified and establish if this can cause departures from universality. In order to explore this dependance, use a set of different DM only cosmological simulations, with the latest cosmo parameters from Planck; this first suite of simulations is followed by a lower resolution set carried out with different cosmo parameters. Identify DM haloes using a Spherical Overdensity algorithm with varying overdensity thresholds (viral, 2000 rho_c, 1000 rho_c, 500 rho_c, 200 rho_c and 200 rho_b) at all redshifts. Notice that, when expressed in terms of the rescaled variable nu, the mass function for viral haloes can be considered universal as a function of redshift and cosmology, while this is clearly no the case for the other considered over densities. Provide fitting functions for the halo mass function parameters as a function of density, that allow to predict, with a few percent accuracy, the halo mass function for a wide range of halo definitions, redshifts and cosmo models. Then present how the departures from universality associated with other halo definitions can be derived by combining the universality of the viral definition with the expected shape of the density profile of haloes.
1507.05647
Mapping ad simulating systematics due to spatially-varying observing conditions in DES Science Verification data
Leistedt, Peiris, et al
Spatially-varying depth and characteristics of observing conditions, such as seeing, airmass, or sky background, are major sources of systematic uncertainties in modern galaxy survey analyses, in particular in deep multi-epoch surveys. Present a framework to extract and project these sources of systematics onto the sky, and apply it to DES to map the observing conditions of the SV data. The resulting distributions and maps of sources of systematics are used in several analysis of DES SV to perform detailed null tests with the data, and also to incorporate systematics in survey simulations. Illustrate the complementarity of these 2 approaches by comparing the SV data with the BCC-UFig, a synthetic sky catalogue generated by forward-modeling of the DES SV images. Analyse the BCC-UFig simulation to construct galaxy samples mimicking those used in SV galaxy clustering studies. Show that the spatially-varying survey depth imprinted in the observed galaxy densities and the redshift distributions of the SV data are successfully reproduced by the simulation and well-captured by the maps of observing conditions. The combined use of the maps, the SV data and the BCC-Fig simulation allows to quantify the impact of spatial systematics on N(z), the redshift distributions inferred using photo-z. Conclude that spatial systematics in the SV data are mainly due to seeing fluctuations and are under control in current clustering and WL analyses. The framework presented here is relevant to all multi-epoch surveys, and will be essential for exploiting future surveys such as LSST, which will require detailed null-tests and realistic end-to-end simulations to correctly interpret the deep-, high-cadence observations of the sky.
1507.05823
Gone without a bang: an archival HST survey for disappearing massive stars
Reynolds, Fraser, Gilmore
Find one candidate between 1994 and 2013 which is consistent with a 25-30 Msun yellow suppressant which has undergone an optically dark core-collapse.
1507.05909
Redshift distribuions of galaxies in the DES science verification shear catalog and implications for weak lensing
Bonnett, et al
Present photometric z estimates for galaxies used in WL analysis of DES SV data. Four model- or machine learning-based photo-z methods - ANNZ2, BPZ calibrated against BCC-fig simulations, SkyNet, and TPZ - are analyzed. For training, calibration, and testing of these methods, construct a catalogue of spectroscopically confirmed galaxies matched against DES SV data. The performance of the methods is evaluated against the matched spectroscopic catalogue, focusing on metrics relevant for WL analysis, with additional validation against COSMOS photo-zs. From the galaxies in the DES SV shear catalogue, which have mean redshift 0.72±0.01 over the range 0.3<z<1.3, construct 3 tomographic bins with means of z={0.45,0.67,1.00}. These bins each have systematic uncertainties delta z<~0.05 in the mean of the fiducial SkyNet photo-z n(z). Propagate the errors in the z distributions through to their impact on cosmological parameters estimated with cosmic shear, and find that they cause shifts in the value of sigma_8 of approx 3%. This shift is within the one sigma statistical errors on sigma8 for the DES SV shear catalog. Further study the potential impact of systematic differences on the critical surface density Sigma_crit, finding levels of bias safely less than the statistical power of DES SV data. Recommend a final Gaussian prior for the photo-z bias in the man of n(z) of width 0.05 for each of the 3 tomographic bins, and show that this is a sufficient bias model for the corresponding cosmology analysis.
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