1806.00014
Approximating photo-$z$ PDFs for large surveys
Malz, Marshall, DeRose, Graham, Schmidt, Wechsler
Monder galaxy surveys produce redshift PDFs in addition to traditional photo-z point estimates. However, the storage of photo-z PDFs may present a challenge with increasingly large catalogs, as we face a trade-off between the accuracy of subsequent science measurements and the limitation of finite storage resources. This paper presents qp, a Python package for manipulating parameterizations of 1D PDFs, as suitable for photo-z PDF compression. Use qp to investigate the performance of 3 simple PDF storage formats (quantiles, samples, and step functions) as a function of the number of stored parameters on 2 realistic mock datasets, representative of upcoming surveys with different data qualities. Propose some best practices for choosing a photo-z PDF approximation scheme and demonstrate the approach on a science case using performance metrics on both ensembles of individual photo-z PDFs and an estimator of the overall z distribution function. Show that both the properties of the set of PDFs that is to be approximated and the chosen fidelity metric(s) affect the optimal parameterization. Additionally, find that quantiles and samples outperform step functions, and it is encouraged to further consider these formats for PDF approximation.
1806.00017
Jacobi Mapping Approach for a precise cosmological weak lensing formalism
Grimm, Yoo
Cosmological WL has been a highly successful and rapidly developing research field since the first detection of cosmic shear in 2000. However, it has recently been pointed out in Yoo+ that the standard WL formalism yields gauge-dependent results and, hence, does not meet the level of accuracy demanded by the next generation of WL surveys. Here, show that the Jacobi mapping formalism provides a solid alternative to the standard formalism, as it accurately describes all the relativistic effects contributing to the WL observables. Calculate gauge-invariant expressions for the distortion in the luminosity distance, the cosmic shear components and the lensing rotation to linear order including scalar, vector and tensor perturbations. In particular, the Jacobi mapping formalism proves that the rotation is fully vanishing to linear order. Furthermore, the cosmic shear components contain an additional term in tensor modes which is absent in the results obtained with the standard formalism. The work provides further support and confirmation of the gauge-invariant lensing formalism needed in the era of precision cosmology.
1806.00018
Is extraterrestrial life suppressed on subsurface ocean worlds due to the paucity of bioessential elements?
Lingam, Loeb
The availability of bioessential elements for "life as we know it", such as P or possibly Mo, is expected to restrict the biological productivity of extraterrestrial biospheres. Here, focus on worlds with subsurface oceans and model the sources and sinks of bioessential elements. Find that the sinks of P are likely to dominate over its sources provided that these oceans are either neutral or alkaline and possess hydrothermal activity. Hence, conclude that the P in sub-surface oceans could be depleted over Myr timescales, thereby leading to oligotrophic or non-existent global biospheres and low chances of life being detected. Along these lines, any potential biosphere in the clouds of Venus may be limited by the availability of Mo. Also point out the possibility that stellar spectroscopy can be used to place potential constraints on the availablitiy of bioessential elements on planets and moons.
1806.00041
The abundance of satellite galaxies in the inner region of $\Lambda$CDM Milky Way sized haloes
Li, Gao, Wang
The concordance LCDM cosmology predicts tens of satellite galaxies distributed in the inner region (<40 kpc) of the MW, yet only 7 were discovered at present day, including 3 discovered recently by DES. Use 5 ultra-high resolution simulations of MW sized DM haloes from the Aquarius project, combined with GalForm semi-analytical galaxy formation model, to investigate properties of the model satellite galaxy population inside 40 kpc of MW sized haloes. On average, in each halo this model predicts about 20 inner satellite galaxies, among them 5 are comparable to the classic satellites in the luminosity, these are in stark contrast to the corresponding numbers in observations. Further investigate the survivability of these model inner satellites in the presence of a central stellar disk with a set of ideal simulations. These are done by re-evolvoing a quarter (30) of the whole Aquarius inner satellite galaxies (121) by including a static disk potential in addition to the MW halo. The finding is that, while the additional disk can completely disrupt some satellites with very close percenters [?], 60% of them could still survive to the present day. This results in 14 satellite galaxies within the 40 kpc of each Aquarius when taking into account of the MW disk, still a factor of 2 more abundant than the observed number. Therefore, unless half a doezen satellite galaxies could be discovered within 40 kpc of the MW by future surveys, the deficiency in the inner satellite galaxy population may post a serious challenge to the standard LCDM theory.
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