1809.06424
The effect of assembly bias on redshift space distortions
Padilla, Contreras, Zehavi, Baugh, Norberg
Study potential systematic effects of assembly bias on cosmological parameter constraints from redshift space distortion measurements. Use a semi-analytic galaxy formation model applied to the Millennium N-body WMAP-7 simulation to study the effects of halo assembly bias on the redshift space distortions of the galaxy correlation function. Look at the pairwise velocities of galaxies living in haloes with concentrations and ages in the upper and lower quintiles, and find that the velocity differences between these are consistent with those reported for real-space clustering analyses, i.e. samples with higher clustering also exhibit stronger infall pairwise motions. This can also be seen in the monopole and quadrupole of the redshift-space correlation function. Find that regardless of the method of measurement, the changes in the beta parameter due to different secondary halo parameters fully tracks the change in the bias parameter. Hence, assembly bias does not introduce detectable systematics in the inferred logarithmic growth factor.
1809.06634
On the degeneracy between baryon feedback and massive neutrinos as probed by matter clustering and weak lensing
Parimbelli, Viel, Sefusatti
Massive neutrinos, due to their free streaming, produce a suppression in the matter PS at intermediate and small scales which could be probed by galaxy clustering and/or weak lensing observables. This effect happens at scales that are also influenced by baryon feedback, i.e., galactic winds or AGN feedback, which in realistic hydrodynamic sims has also been show to produce a suppression of power. Leaving aside for the moment the complex issue of galaxy bias, focus here on matter clustering and tomographic WL, investigate the possible degeneracy between baryon feedback and neutrinos showing that it is not likely to degrade significantly the measurement of neutrino mass in future surveys. To do so, generate mock data sets and fit them using MCMC technique and explore degeneracies between feedback parameters and neutrino mass. Model baryon feedback through fitting functions, while massive neutrinos are accounted for, also in the non-linear regime, using Halofit calibrated against accurate N-body neutrino simulations. In the error budget, include the uncertainty in the modeling of nonlinearities. For both matter clustering and WL, always recover the input neutrino mass within ~0.25 sigma CL. Finally, also take into account the intrinsic alignment effect in the WL mock data. Even in this case, able to recover the right parameters: in particular, find a significant degeneracy pattern between M_nu and the IA parameter A_IA.
1809.06960
Strange messenger: a new history of hydrogen on Earth, as told by Xenon
Zahnle, Gacesa, Catling
Atmospheric Xe is strongly mass fractionated, the result of a process that apparently continued through the Archean and perhaps beyond. Previous models that explain Xe fractionation by hydrodynamic H escape cannot gracefully explain how Xe escaped and Ar and Kr did not, nor allow Xe to escape in the Archean. Here show that Xe is the only noble gas that can escape as an ion in a photo-ionized H wind, possible in the absence of a geomagnetic field or along polar magnetic field lines that open into interplanetary space. To quantify the hypothesis, construct new 1D models of hydrodynamic diffusion-limited H escape from highly-irradiated CO_2-H_2-H atmospheres. The models reveal 3 minimum requirements for Xe escape: solar EUV irradiation needs to exceed 10x that of the modern Sun; the total H mixing ratio in the atmosphere needs to exceed 1% (equiv. to 0.5% CH_4); and transport amongst the ions in the lower ionosphere needs to lift the Xe ions to the base of the outflowing H corona. The long duration of Xe escape implies that, if a constant process, Earth lost the H from at least one ocean of water, roughly evenly split between the Hadean and the Archean. However, to account for both Xe's fractionation and also its depletion with respect to Kr and primordial 244Pu, Xe escape must have been limited to small apertures or short episodes, which suggests that Xe escape was restricted to polar windows by a geomagnetic fields, or dominated by outbursts of high solar activity, or limited to transient episodes of abundant H, or a combination of these. Xe escape stopped when the H (or methane) mixing ratio became too small, or EUV radiation from the aging Sub became too weak, or charge exchange between Xe^+ and O_2 rendered Xe neutral.
1809.07255
Shape of dark matter haloes in the Illustris Simulation: effects of baryons
Chua, Pillepich, Vogelsberger, Hernquist
Study the effect of baryonic processes on the shapes of DM haloes from Illustris, a suite of hydro (Illustris) and DM-only (Illustris-Dark) cosmo sims performed with the moving-mesh code (arepo). DM halo shapes are determined using an interactive method based on the inertia tensor for a wide range of z=0 masses (M_200=[1e11, 3e14] Msun). Convergence tests shows that the local DM shape profiles are converged only for r>9 epsilon, epsilon being the Plummer-equivalent softening length, larger than expected. Haloes from non-radiative sims (i.e. neglecting radiative processes, SF, and feedback) exhibit no alteration in shapes from their DM-only counterparts: thus moving-mesh hydrodynamics alone is insufficient to cause differences in DM shapes. With the full galaxy-physics implementation, condensation of baryons results in significantly rounder and more oblate haloes, with the median minor-to-major axis ratio <c/a>~0.7, almost invariant throughout the halo and across halo masses. This somewhat improves the agreement between simulation predictions and observational estimates of the MW halo shape. Consistently, the velocity anisotropy of DM is also reduced in Illustris, across halo masses and radii. Within the inner halo (r-0.15 R_200), both s and q (intermediate-to-major axis ratio) exhibit non-monotonicity with galaxy mass, peaking at m*~1e[10.5-11] Msun, which is found due to the strong dependence of inner halo shape with galaxy formation efficiency. Baryons in Illustris affect the correlation of halo shape with halo properties, leading to a positive correlation of sphericity of MW-mass haloes with halo formation time and concentration, the latter being mildly more pronounced than in Illustris-Dark.
1809.07341
Survey of Gravitationally-lensed Objects in HST Imaging (SuGOHI). II. Environments and line-of-sight structure of strong gravitational lens galaxies to z~0.8
Wong, et al
Investigate the local and line-of-sight overdensities of strong GLs using wide-area multi band imaging from the HSC Subaru Strategic Program. Present 41 new definite or probable lens candidates discovered in DR2 of the survey. Using a combined sample of 87 galaxy-scale lenses out to a lens redshift of z_L~0.8, compare galaxy number counts in lines of sight toward known and newly-discovered lenses in the survey to those of a control sample consisting of random line-of-sight. Also compare the local overdensity of lens galaxies to a sample of "twin" galaxies that have a similar redshift and velocity dispersion to test whether lenses lie in different environments from similar non-lens galaxies. Find that lens fields contain higher number counts of galaxies compared to the control fields, but this effect arises from the local environment of the lens. Once galaxies in the lens plane are removed, the lens lines of sight are consistent with the control sample. The local environments of the lenses are overdense compared to the control sample, and are slightly overdense compared to those of the twin sample, although the significance is marginal. There is no significant evidence of the evolution of the local overdensity of lens eivnormnents with redshift.
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