1810.12321
Estimates for the impact of ultraviolet background fluctuations on galaxy clustering measurements
Sanderbeck, et al
Spatial fluctuations in ultraviolet backgrounds can subtly modulate the distribution of extragalactic sources, a potential signal and systematic for large-scale structure surveys. While this modulation has been shown to be significant for 3d Ly-alpha forest surveys, its relevance for other large-scale structure robes has not been explored, despite being the only astrophysical process that likely can affect clustering measurements on greater than megaparsec scales. Estimate that background fluctuations, modulating the amount of HI, have a fractional effect of (0.03-0.3)(k/1e-2 Mpc^{-1})^{-1} on the power spectrum of 21cm intensity maps at z=1-3. Find a somewhat smaller effect for H-alpha and Ly-alpha intensity mapping surveys of (0.001-0.1) (k/1e-2 Mpc^{-1})^{-1} and even smaller effect for a more traditional survey that correlates the positions of individual H-alpha or Ly-alpha emitters. Also provide an estimate for the effect of backgrounds on low-z galaxy surveys in general based on a simple model in which ionizing background fluctuations modulate the rate halo gas cools, which then sources star formation. Estimate a maximum fractional effect on the power of ~0.01(k/1e-2 Mpc^{-1})^{-1} at z=1. Compare the sizes of these imprints to cosmological parameter benchmarks for the next generation of z surveys: find that ionizing backgrounds could result in a bias on the squeezed triangle non-Gaussianity parameter f_NL that can be larger than city for PS measurements with a SPHEREx-like galaxy survey, and typical value of intensity bias. Marginalizing over a shape of the form k^{-1} P_L, where P_L is the linear matter power spectrum, removes much of this bias at the cost of ~40% larger statistical errors.
1810.13270
Statistical analysis of binary stars from the Gaia catalogue DR2
Zavada, Piska
A general statistical procedure for analysis of 2D and 3D finite patterns have been developed. A previous application to the data from Gaia-ESA catalogue DR1 has shown high sensitivity to the statistical occurrence of binary and ternary stars systems. In the present study, analyze the data from recently released catalogue DR2, where the use of parallaxes enables to determine the 3D position of the sources. Corresponding patterns represent an input for 3D analysis. The 2D analysis very clearly confirms the former results in the presence of binaries. At the same time, demonstrate that the new 3D analysis also provides a high rate of binaries in the region under study. Moreover, the 3d statistical analysis allows estimation of a high limit of separation of binaries in the same region: Delta_max ~0.1 pc.
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