2010.05934
Spectroscopic classification of a complete sample of astrometrically-selected quasar candidates using Gaia DR2
Heintz, et al
Here we explore the efficiency and fidelity of a purely astrometric selection of quasars as point sources with zero proper motions in the {\it Gaia} data release 2 (DR2). We have built a complete candidate sample including 104 Gaia-DR2 point sources brighter than $G<20$ mag within one degree of the north Galactic pole (NGP), all with proper motions consistent with zero within 2$\sigma$ uncertainty. In addition to pre-existing spectra, we have secured long-slit spectroscopy of all the remaining candidates and find that all 104 stationary point sources in the field can be classified as either quasars (63) or stars (41). The selection efficiency of the zero-proper-motion criterion at high Galactic latitudes is thus $\approx 60\%$. Based on this complete quasar sample we examine the basic properties of the underlying quasar population within the imposed limiting magnitude. We find that the surface density of quasars is 20 deg$^{-2}$, the redshift distribution peaks at $z\sim1.5$, and that only eight systems ($13^{+5}_{-3}\%$) show significant dust reddening. We then explore the selection efficiency of commonly used optical, near- and mid-infrared quasar identification techniques and find that they are all complete at the $85-90\%$ level compared to the astrometric selection. Finally, we discuss how the astrometric selection can be improved to an efficiency of $\approx70\%$ by including an additional cut requiring parallaxes of the candidates to be consistent with zero within 2$\sigma$. The selection efficiency will further increase with the release of future, more sensitive astrometric measurement from the Gaia mission. This type of selection, purely based on the astrometry of the quasar candidates, is unbiased in terms of colours and emission mechanisms of the quasars and thus provides the most complete census of the quasar population within the limiting magnitude of Gaia.
2010.05962
Remarkable migration of the solar system from they innermost Galactic disk; a wander, a wobble, and a climate catastrophe on the Earth
Tsujimoto, Baba
Recent knowledge of Galactic dynamics suggests that stars radially move on the disk when they encounter transient spiral arms that are naturally generated during the process of disk formation. We argue that a large movement of the solar system from the innermost disk over its lifetime is inferred from a comparison of the solar composition with those of solar twins within the Galactic chemical evolution framework. The implied metal-rich environment at the Sun's birthplace and formation time is supported by measured silicon isotopic ratios in presolar silicon carbide grains. We perform numerical simulations of the dynamical evolution of disk stars in a Milky Way-like galaxy to identify the lifetime trajectory of the solar system. We find that a solar system born in the proximity of the Galactic bulge could travel to the current locus by the effect of radial migration induced by several major encounters with spiral arms. The frequent feature we identify is the repeated passages of stars inside the same spiral arm owing to the wobble of stars traveling in and out of the spiral arms. We predict that such episodes are evidenced in the Earth's geological history as snowball Earth and that their occurrence times are within our prediction. In particular, the stellar motion that vertically oscillates during passages through spiral arms occasionally leads to a split into two discrete passage episodes with an interval of several tens of Myr, implying two relevant snowball Earth events that occurred in rapid succession (~7.2 and 6.5 hundred Myr ago).
2010.06064
The End of Galaxy Surveys
Rhodes, Huff, Masters, Nierenberg
For nearly a century, imaging and spectroscopic surveys of galaxies have given us information about the contents of the universe. We attempt to define the logical endpoint of such surveys by defining not the next galaxy survey, but the final galaxy survey at NIR wavelengths; this would be the galaxy survey that exhausts the information content useful for addressing extant questions. Such a survey would require incredible advances in a number of technologies and the survey details will depend on the as yet poorly constrained properties of the earliest galaxies. Using an exposure time calculator, we define nominal surveys for extracting the useful information for three science cases: dark energy cosmology, galaxy evolution, and supernovae. We define scaling relations that trade off sky background, telescope aperture, and focal plane size to allow for a survey of a given depth over a given area. For optimistic assumptions, a 280m telescope with a marginally resolved focal plane of 20 deg$^2$ operating at L2 could potentially exhaust the cosmological information content of galaxies in a 10 year survey. For galaxy evolution (making use of gravitational lensing to magnify the earliest galaxies) and SN, the same telescope would suffice. We discuss the technological advances needed to complete the last galaxy survey. While the final galaxy survey remains well outside of our technical reach today, we present scaling relations that show how we can progress toward the goal of exhausting the information content encoded in the shapes, positions, and colors of galaxies.
2010.07376
Probing dark energy with tomographic weak-lensing aperture mass statistics
Matrinet, et al
We forecast and optimize the cosmological power of various weak-lensing aperture mass ($M_{\rm ap}$) map statistics for future cosmic shear surveys, including peaks, voids, and the full distribution of pixels (1D $M_{\rm ap}$). These alternative methods probe the non-Gaussian regime of the matter distribution, adding complementary cosmological information to the classical two-point estimators. Based on the SLICS and cosmo-SLICS $N$-body simulations, we build Euclid-like mocks to explore the $S_8 - \Omega_{\rm m} - w_0$ parameter space. We develop a new tomographic formalism which exploits the cross-information between redshift slices (cross-$M_{\rm ap}$) in addition to the information from individual slices (auto-$M_{\rm ap}$) probed in the standard approach. Our auto-$M_{\rm ap}$ forecast precision is in good agreement with the recent literature on weak-lensing peak statistics, and is improved by $\sim 50$% when including cross-$M_{\rm ap}$. It is further boosted by the use of 1D $M_{\rm ap}$ that outperforms all other estimators, including the shear two-point correlation function ($\gamma$-2PCF). When considering all tomographic terms, our uncertainty range on the structure growth parameter $S_8$ is enhanced by $\sim 45$% (almost twice better) when combining 1D $M_{\rm ap}$ and the $\gamma$-2PCF compared to the $\gamma$-2PCF alone. We additionally measure the first combined forecasts on the dark energy equation of state $w_0$, finding a factor of three reduction of the statistical error compared to the $\gamma$-2PCF alone. This demonstrates that the complementary cosmological information explored by non-Gaussian $M_{\rm ap}$ map statistics not only offers the potential to improve the constraints on the recent $\sigma_8$ - $\Omega_{\rm m}$ tension, but also constitutes an avenue to understand the accelerated expansion of our Universe.
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