Monday. Tuesday.
1707.04253
The resilience of life to astrophysical events
Sloan, Batista, Loeb
Much attention has been given in the literature to the effects of astrophysical events on human and land-based life. However, little has been discussed on the resilience of life itself. Instead explore the statistics of events that completely sterilize an Earth-like planet with planet radii in the range 0.5-1.5 R_Earth and temperatures of ~300K, eradicating all forms of life. Consider the relative likelihood of complete global sterilization events from three astrophysical sources -- SNe, gamma-ray bursts, large asteroid impacts, and passing-by stars. To assess such probabilities consider what cataclysmic event could lead to the annihilation of not just human life, but also extremophiles, through the boiling of all water in Earth's oceans. Surprisingly find that the although human life is somewhat fragile to nearby events, the resilience of Ecdysozoa such as Milnesium tardigradum renders global sterilization an unlikely event.
1707.04256
Small-scale challenges to the $\Lambda$CDM Paradigm
Bullock, Boylan-Kolchin
The DE plus cold dark matter (LCDM) cosmological model has been a demonstrably successful framework for predicting and explains the large-scale structure of Universe and its evolution with time. Yet on length scales smaller than ~1 Mpc and mass scales smaller than ~1e11 Msun, the theory faces a number of challenges. For example, the observed cores of many DM dominated galaxies are both less dense and less cuspy than naively predicted in LCDM. The number of small galaxies and dwarf satellites in the Local Group is also far below the predicted count of low-mass DM haloes and subheads within similar volumes. These issues underlie the most well-documented problems with LCDM: Cusp/Core, Missing Satellites, and Too-Big-to-Fail. The key questions is whether a better understanding of baryon physics, DM physics, or both will be required to meet these challenges. Other anomalies, including the observed planar and orbital configurations of Local Group satellites and the tight baryonic/dark matter scaling relations obeyed by the galaxy population, have been less thoroughly explored in the context of LCDM theory. Future surveys to discover faint, distant dwarf galaxies and to precisely measure their masses and density structure hold promising avenues for testing possible solutions to the small-scale challenges going forward. Observational programs to constrain or discover and characterize the number of truly dark low-mass halos are among the most important, and achievable, goals in this field over the next decade. These efforts will either further verify the LCDM paradigm or demand a substantial revision in the understanding of the nature of dark matter.
1707.04267
Predicting structures in the zone of avoidance
Source, et al
The Zone of Avoidance (ZOA), whose emptiness is an artifact of our Galaxy dust, has been challenging observers as well as theoretisch for many years. Multiple attempts have been made on the observational side to maps this region in order to better understand the local flows. On the theoretical side, however, this region is often simply statistically populated with structures but no real attempt has been made to confront theoretical and observed matter distributions. This paper takes a step forward using constrained realizations of the local Universe shown to be perfect substitutes of local Universe-like simulations for smooth high density peak studies. Far from generating completely 'random' structures in the ZOA, the reconstruction technique arranges matter according to the surrounding environment of this region. More precisely, the mean distributions of structures in a series of constrained and random realizations differ: while densities annihilate each other when averaging over 200 random realizations, structures persist when summing 200 constrained realizations. The probability distribution function of ZOA grid cells to be highly overdense is a Gaussian with a 15% mean in the random case, while that of the constrained case exhibits large tails. This implies that areas with the largest probabilities host most likely a structure. Comparisons between these predictions and observations, like this of the Puppis 3 cluster, show a remarkable agreement and allow us to assert the presence of the recently highlighted by observations, Vela supercluster at about 180 Mpc/h, right behind the thickest dust layers of our Galaxy.
1707.04334
Impications of a wavelength dependent PSF for weak lensing measurements
Eriksen, Hoekstra
The convolution of galaxy images by PSF is the dominant source of bias for WL studies, and an accurate estimate of the PSF is required to obtain unbiased shape measurements. The PSF estimate for a galaxy depends on its SED, because the instrumental PSF is generally a function of the wavelength. In this paper, explore various approaches to determine the resulting 'effective' PSF using broad-band data. Considering the Euclid mission as a reference, find that standard SED template fitting methods result in biases that depend on source redshift, although this may be remedied if the algorithms can be optimized for this purpose. Using a machine-learning algorithm, show that, at least in principle, the required accuracy can be achieved with the current survey parameters. It is also possible to account for the correlations between photometric redshift and PSF estimates that arise from the use of the same photometry. Explore the impact of errors in photometric calibrations, errors in the assumed wavelength dependence of the PSF model and limitations of the adopted template libraries. The results indicate that the required accuracy for Euclid can be achieved using the data that are planed to determine photometric redshifts.
1707.04488
On the insufficiency of arbitrarily precise covariance matrices
Sellentin, Heavens
Investigate whether a Gaussian likelihood, as routinely assumed in the analysis of cosmological data, is supported by simulated survey data. Define test statistics, based on a novel method that first destroys Gaussian correlations in a dataset, and then measures the non-Gaussian correlations that remain. This procedure flags pairs of datapoints which depend on each other in a non-Gaussian fashion, and thereby identifies where the assumption of a Gaussian likelihood breaks down. Using this diagnostic, find that non-Gaussian correlations in the CHFTLenS cosmic shear correlation functions are significant. With a simple exclusion of the most contaminated datapoints, the posterior for s8 is shifted without broadening, but find no significant reduction in the tension with s8 derived from Planck CMB data. However, also show that the one-point distributions of the correlation statistic are noticeably skewed, such that sound WL data sets are intrinsically likely to lead to a systematically low lensing amplitude being inferred. The detected non-Gaussianities get larger with increasing angular scale such that for future wide-angle surveys such as Euclid or LSST, with their very small statistical errors, the large-scale modes are expected to be increasingly affected. The shifts in posteriors may then not be negligible and recommend that these diagnostic tests by run as part of future analyses.
1707.04590
On the power spectrum of dark matter substructure in strong gravitational lenses
Rivero, Cyr-Racine, Dvorkin
Studying the smallest self-bound dark matter structure n the Universe can yield important clues about the fundamental particle nature of dark matter. Galaxy-sacle strong gravitational lensing provides a unique way to detect and characterize DM substructures at cosmological distances from the MW. Within the CDM paradigm, the number of low-mass sub haloes within lens galaxies is expected to be large, implying that their contribution to the lensing convergence field is approximately Gaussian and could thus be described by their power spectrum. Develop here a general formalism to compute from first principles the subscturture convergence power spectrum for different populations of DM sub halos. As an example, apply the framework to 2 distinct sub halo populations: a truncated NFW sub halo population motivated by standard CDM, and a truncated cored sub halo population motivated by self-interacting dark matter (SIDM). Study in detail how the subhead abundance, mass function, internal density profile, and concentration affect the amplitude and shape of substructure power spectrum. Determine that the power spectrum is mostly sensitive to a specific combination of the sub halo abundance and moments of the mass function, as well as to the average tidal truncation scale of the largest sub halos included in the analysis. Interestingly, show that the asymptotic slope of the subscturture power spectrum at large wavenumber reflects the internal density profile of the sub halos. In particular, the SIDM power spectrum exhibits a characteristic steepening at large wavenumber absent in the CDM power spectrum, opening the possibility of using this observable, if at all measurable, to discern between these 2 scenarios.
1707.04594
Implications of tides for life on exoplanets
Lingam, Loeb
As evident from the nearby examples of Proxima Centauri and TRAPPIST-1, Earth-sized planets in the habitable zone of low-mass stars are common. Here, focus on such planetary systems and argue that their (oceanic) tides could be more prominent due to stronger tidal forces. Identify the conditions under which tides may exert a significant positive influence on biotic processes - abiogenesis, biological rhythms and stimulating photosynthesis. Conclude the analysis by identifying large-scale algal blooms as potential temporal biosignatures in reflectance light curves that can arise indirectly as a consequence of strong tidal forces.
1707.04606
The discovery of a gravitationally lensed supernova Ia at redshift 2.22
Rubin, et al
Present the discovery and measurements of a gravitationally lensed supernova (SN) behind the galaxy cluster MOO J1014+0038. Based on multi-band HST and VLT photometry and spectroscopy, find a 99% probability that the SN is a SN Ia, and a 1% chance of a CC SN. The typing algorithm combines the shape and color of the light curve with the expected rates of each SN type in the host galaxy. With a redshift of 2.2216, this is the highest redshift SN Ia discovered with a spectroscopic host-galaxy redshift. A further distinguishing feature is that the lensing cluster, at z=1.23, is the most distant to date to have an amplified SN. The SN lies in the middle of the color and light-curve shape distributions found at lower z, disfavoring strong evolution to z=2.22. Estimate an amplification of 2.8+0.6-0.5 (1.10±0.23 mag) --- compatible with the value estimated from WL-derived mass and the mass-concentration relation from LCDM simulations --- making it the most amplified SN Ia discovered behind a galaxy cluster.
1707.04924
The dependence of halo mass on galaxy size at fixed stellar mass using weak lensing
Charlton, et al
Stellar mass has been show to correlate with halo mass, with non-negligible scatter. The stellar mass-size and luminosity-size relationships of galaxies also show significant scatter in galaxy size at fixed stellar mass. It is possible that, at fixed stellar mass and galaxy color, the halo mass is correlated with galaxy size. Galaxy-galaxy lensing allows us to measure the mean masses of dark matter haloes for stacked samples of galaxies. Extend the analysis of the galaxies in the CFHTLenS catalogue by fitting single Sersic surface brightness profiles to the lens galaxies in order to recover half-light radius values, allowing determination of halo masses for lenses according to their size. Comparing the halo masses and sizes to baselines for that stellar mass yields a differential measurement of the halo mass-galaxy size relationship at fixed stellar mass, defined as Mh(M*)~r_eff^eta(M*). Find that on average, the lens galaxies have an eta=0.42±0.12, i.e. larger galaxies live in more massive DM haloes. The eta is strongest for high mass LRGs. Investigation of this relationship in hydro sims suggests that, at a fixed M*, satellite galaxies have a larger eta and greater scatter in the Mh and r_eff relationship compared to central galaxies.
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