1711.06692
Influence of XUV Irradiation from Sgr A* on planetary habitability and occurrence of panspermia near the Galactic center
Chen, Forbes, Loeb
Find that, out to ~20 pc from Sgr A*, the XUV flux emitted during its quasar phase can remove several percent of a planet's H/He envelope by mass; in many cases, this removal results in bare rocky cores, many of which situated in the habitable zones (HZs) of G-type stars. The erosion of sub-neptune sized planets may be one of the most prevalent channels by which terrestrial super-Earths are created near the GalacticCenter. As such, the planet population demographics may be quite different close to Sgr A* than in the Galaxy's outskirts. The high stellar densities in this region (about seven orders of magnitude greater than the solar neighborhood) imply that the distance between neighboring rocky worlds is short (500-5000AU). The proximity between potentially habitable terrestrial planets may enable the onset of widespread interstellar panspermia near the nuclei of galaxies. More generally, predict these phenomena to be ubiquitous for planets in nuclear star clusters (NSCs) and ultra-compact dwarfs (UCDs).
1711.06801
Whole planet coupling between climate, mantle, and core: implications for the evolution of rocky planets
Foley, Driscoll
Earth's climate, mantle, and core interact over geologic timescales. Climate influences whether plate tectonics can take place on a planet, with cool climates being favorable for plate tectonics because they enhance stresses in the lithosphere, suppress plate boundary annealing, and promote hydration and weakening of the lithosphere. Plate tectonics plays a vital role in the long-term carbon cycle, which helps to maintain a temperate climate. Plate tectonics provides long-term cooling of the core, which is vital for generating a magnetic field, and the magnetic field is capable of shielding atmospheric volatiles from the solar wind. Coupling between climate, mantle, and core can potentially explain the divergent evolution of Earth and Venus. As Venus lies too close to the sun for liquid water to exist, there is no long-term carbon cycle and thus an extremely hot climate. Therefore plate tectonics cannot operate and a long-lived core dynamo cannot be sustained due to insufficient core cooling. On planets within the habitable zone where liquid water is possible, a wide range of evolutionary scenarios can take place depending on initial atmospheric composition, bulk volatile content, or the timing of when plate tectonics initiates, among other factors. Many of these evolutionary trajectories would render the planet uninhabitable. However, there is still significant uncertainty over the nature of the coupling between climate, mantle, and core. Future work is needed to constrain potential evolutionary scenarios and the likelihood of an Earth-like evolution.
1711.06863
Chasing the peak: optimal statistics for weak shear analysis
Smit, Kuijken
WL analyses are fundamentally limited by the intrinsic, non-Gaussian distribution of galaxy shapes. Explore alternate statistics for samples of ellipticity measurements that are unbiased, efficient, and robust. Take the non-linear mapping of gravitational shear and the effect of noise into account. Then discuss how the distribution of individual galaxy shapes in the observed field of view can be modeled by fitting Fourier modes to the shear pattern directly. Simulate samples of galaxy ellipticities, using both theoretical distributions and real data for ellipticities and noise; determine the possible bias Delta e, the efficiency eta and the robustness of the least absolute deviations, the biweight, and the convex hull peeling estimators, compared to the canonical weighted mean. Using these statistics for regression, show the applicability of direct Fourier mode fitting. These estimators can be unbiased in the absence of noise, and decrease noise bias by more than ~30%. The convex hull peeling estimator distribution is centered around the underlying shear, and its bias least affected by noise. The least absolute deviations estimator is found to be the most efficient estimator in almost all cases, except in the Gaussian case, where it's still competitive (0.83<eta<5.1) and therefore robust. These results hold when fitting Fourier modes, where amplitudes of variation in ellipticity are determined to the order of 1e-3. The peak of the ellipticity distribution is a direct tracer of the underlying shear and unaffected by noise; show that estimators that are sensitive to a central cusp perform more efficiently, potentially reducing uncertainties by more than 50% and significantly decreasing noise bias.
1711.07297
Models of gravitational lens candidates from Space Warps CFHTLS
Küng, Saha, et al
Report modeling follow-up of recently-discovered gravitational-lens candidates in CFHTLS. Lens modeling was done by a small group of specially-interested volunteers from the SpaceWarps citizen-science community who originally found the candidate lenses. Models are categorized according to 7 diagnostics indicating (a) the image morphology and how clear or indistinct it is, (b) whether the mass map and synthetic lensed image appear to be plausible, and (c) how the lens-model mass compares with the stellar mass and the abundance-matched halo mass. The lensing masses range from ~1e11 Msun to >1e13 Msun. Preliminary estimates of the stellar masses show a smaller spread in stellar mass (except for two lenses): a factor of a few below or above ~1e11 Msun. Therefore, expect the stellar-to-total mass fraction to decline sharply as lensing mass increases. The most massive system with a convincing model is J1434+522 (SW05). The two low-mass outliers are J0206-095 (SW19) and J2217+015 (SW42); if these two are indeed lenses, they probe an interesting regime of very low SF efficiency. Some improvements to the modeling software (SpaghettiLens), and discussion of strategies regarding scaling to future surveys with more and frequent discoveries, are included.
1711.07467
Complete super-sample lensing covariance n the response approach
Barreira, Krause, Schmidt
Derive the complete SSC of the matter and WL convergence power spectra using the PS response formalism to accurately describe the coupling of super-to-intra survey modes. The SSC term is completely characterized by the survey window function, the NL matter PS and the full first-order NL power spectrum response function, which describes the response to SS density and tidal field perturbations. Separate universe simulations can efficiently measure these responses in the NL regime of structure formation, which is necessary for lensing applications. Under the Limber and flat-sky approximations, show that the tidal contributions, which have not been included in cosmological analyses so far, represent a significant fraction (~20-25%) of the total SSC, even for an isotropic survey footprint on the sky. The SSC is the dominant off-diagonal contribution to the total lensing covariance for survey sky fractions f_sky <~0.3, making it important to include these tidal terms in cosmic shear analyses.
1711.07919
A quadruply lensed SN Ia: gaining a time-delay...losing a standard candle
Yahalomi, Schechter, Wambsganss
Investigate the flux ratio anomalies between macro-model predictions and the observed rightness of the SN iPDF16geu, as published in a recent paper by More+ 2017. This group suggested that these discrepancies are, qualitatively, likely due to microlensing. Analyze the plausibility of attributing this discrepancy to microlensing, and find that the discrepancy is too large to be due to microlensing alone. This is true whether one assumes knowledge of the luminosity of the SN or allows the luminosity to be a free parameter. Varying the dark/stellar ratio likewise doesn't help. In addition, other macro-models with quadruplicity from external shear or ellipticity do not significantly improve to model. Finally, microlensing also makes it difficult to accurately determine the standard candle brightness of the SN, as the likelihood plot for the intrinsic magnitude of the source (for a perfect macro-model) has a FWHM of 0.73 magnitudes. As such, the error for the standard candle brightness is quite large. This reduces the utility of the standard candle nature of type Ia SN.
No comments:
Post a Comment