1905.06954
Prospects for observing the cosmic web in Lyman-{\alpha} emission
Wistok, et al
Mapping the intergalactic medium (IGM) in Lyman-$\alpha$ emission would yield unprecedented tomographic information on the large-scale distribution of baryons and potentially provide new constraints on the UV background and various feedback processes relevant for galaxy formation. Here, we examine the Lyman-$\alpha$ emission of the moderate-density IGM due to collisional excitations and recombinations in the presence of a UV background in the Sherwood simulation suite. We focus on large-scale-structure filaments in which Lyman-$\alpha$ radiative transfer effects are expected to be moderate. At low density the emission is primarily due to fluorescent re-emission of the ionising UV background due to recombinations, while collisional excitations dominate at higher densities. We discuss prospects of current and future observational facilities to detect this emission and focus on VLT/MUSE for a more detailed sensitivity analysis. We construct mock MUSE observations resembling the MUSE Hubble Deep Field South from our simulations and show that our predictions are consistent with recent analyses of diffuse Lyman-$\alpha$ emission using MUSE at redshifts $3 < z < 6$. We find that it should be most feasible to detect the Lyman-$\alpha$ emission from filaments in the IGM in overdense regions, somewhat surprisingly towards the high-redshift end ($z \gtrsim 4.5$) accessible by MUSE, and if narrowband widths close to the MUSE spectral resolution limit are used. This is due to the higher densities and lower temperatures in the IGM at higher redshift. High-redshift protoclusters therefore appear to be the ideal environment to observe filamentary structures in the IGM in Lyman-$\alpha$ emission.
Prospects for observing the cosmic web in Lyman-{\alpha} emission
Wistok, et al
Mapping the intergalactic medium (IGM) in Lyman-$\alpha$ emission would yield unprecedented tomographic information on the large-scale distribution of baryons and potentially provide new constraints on the UV background and various feedback processes relevant for galaxy formation. Here, we examine the Lyman-$\alpha$ emission of the moderate-density IGM due to collisional excitations and recombinations in the presence of a UV background in the Sherwood simulation suite. We focus on large-scale-structure filaments in which Lyman-$\alpha$ radiative transfer effects are expected to be moderate. At low density the emission is primarily due to fluorescent re-emission of the ionising UV background due to recombinations, while collisional excitations dominate at higher densities. We discuss prospects of current and future observational facilities to detect this emission and focus on VLT/MUSE for a more detailed sensitivity analysis. We construct mock MUSE observations resembling the MUSE Hubble Deep Field South from our simulations and show that our predictions are consistent with recent analyses of diffuse Lyman-$\alpha$ emission using MUSE at redshifts $3 < z < 6$. We find that it should be most feasible to detect the Lyman-$\alpha$ emission from filaments in the IGM in overdense regions, somewhat surprisingly towards the high-redshift end ($z \gtrsim 4.5$) accessible by MUSE, and if narrowband widths close to the MUSE spectral resolution limit are used. This is due to the higher densities and lower temperatures in the IGM at higher redshift. High-redshift protoclusters therefore appear to be the ideal environment to observe filamentary structures in the IGM in Lyman-$\alpha$ emission.
1905.07024
Probing galaxy assembly bias in BOSS galaxies using void probabilities
Walsh, Tinker
We measure the void probability function (VPF) of galaxies in the Baryon Oscillation Spectroscopic Survey (BOSS). The VPF provides complementary information to standard two-point statistics in that it is sensitive to galaxy bias in the most extreme underdensities in the cosmic web. Thus the VPF is ideal for testing whether halo occupation of galaxies depends on large-scale density, an effect known as galaxy assembly bias. We find that standard HOD model---one parameterized by halo mass only---fit only to the two-point function, accurately predicts the VPF. Additionally, for HOD models where density dependence is explicitly incorporated, the best-fit models fit to the combination of the correlation function and the VPF have zero density dependence. Thus galaxy assembly bias is not a strong source of systematic uncertainty when modeling the clustering of massive galaxies.
1905.07070
The detectability and characterization of the TRAPPIST-1 exoplanet atmospheres with JWST
Lustig-Yaeger, et al
The James Webb Space Telescope (JWST) will offer the first opportunity to characterize terrestrial exoplanets with sufficient precision to identify high mean molecular weight atmospheres, and TRAPPIST-1's seven known transiting Earth-sized planets are particularly favorable targets. To assist community preparations for JWST, we use simulations of plausible post-ocean-loss and habitable environments for the TRAPPIST-1 exoplanets, and test simulations of all bright object time series spectroscopy modes and all MIRI photometry filters to determine optimal observing strategies for atmospheric detection and characterization using both transmission and emission observations. We find that transmission spectroscopy with NIRSpec Prism is optimal for detecting terrestrial, CO2 containing atmospheres, potentially in fewer than 10 transits for all seven TRAPPIST-1 planets, if they lack high altitude aerosols. If the TRAPPIST-1 planets possess Venus-like H2SO4 aerosols, up to 12 times more transits may be required to detect atmospheres. We present optimal instruments and observing modes for the detection of individual molecular species in a given terrestrial atmosphere and an observational strategy for discriminating between evolutionary states. We find that water may be prohibitively difficult to detect in both Venus-like and habitable atmospheres due to its presence lower in the atmosphere where transmission spectra are less sensitive. Although the presence of biogenic O2 and O3 will be extremely challenging to detect, abiotically produced oxygen from past ocean loss may be detectable for all seven TRAPPIST-1 planets via O2-O2 collisionally-induced absorption at 1.06 and 1.27 microns, or via NIR O3 features for the outer three planets. Our results constitute a suite of hypotheses on the nature and detectability of highly-evolved terrestrial exoplanet atmospheres that may be tested with JWST.
The detectability and characterization of the TRAPPIST-1 exoplanet atmospheres with JWST
Lustig-Yaeger, et al
The James Webb Space Telescope (JWST) will offer the first opportunity to characterize terrestrial exoplanets with sufficient precision to identify high mean molecular weight atmospheres, and TRAPPIST-1's seven known transiting Earth-sized planets are particularly favorable targets. To assist community preparations for JWST, we use simulations of plausible post-ocean-loss and habitable environments for the TRAPPIST-1 exoplanets, and test simulations of all bright object time series spectroscopy modes and all MIRI photometry filters to determine optimal observing strategies for atmospheric detection and characterization using both transmission and emission observations. We find that transmission spectroscopy with NIRSpec Prism is optimal for detecting terrestrial, CO2 containing atmospheres, potentially in fewer than 10 transits for all seven TRAPPIST-1 planets, if they lack high altitude aerosols. If the TRAPPIST-1 planets possess Venus-like H2SO4 aerosols, up to 12 times more transits may be required to detect atmospheres. We present optimal instruments and observing modes for the detection of individual molecular species in a given terrestrial atmosphere and an observational strategy for discriminating between evolutionary states. We find that water may be prohibitively difficult to detect in both Venus-like and habitable atmospheres due to its presence lower in the atmosphere where transmission spectra are less sensitive. Although the presence of biogenic O2 and O3 will be extremely challenging to detect, abiotically produced oxygen from past ocean loss may be detectable for all seven TRAPPIST-1 planets via O2-O2 collisionally-induced absorption at 1.06 and 1.27 microns, or via NIR O3 features for the outer three planets. Our results constitute a suite of hypotheses on the nature and detectability of highly-evolved terrestrial exoplanet atmospheres that may be tested with JWST.
1905.07343
Does the evolution of complex life depend on the stellar spectral energy distribution?
Haqq-Misra
This paper presents the proportional evolutionary time hypothesis, which posits that the mean time required for the evolution of complex life is a function of stellar mass. The "biological available window" is defined as the region of a stellar spectrum between 200 to 1200 nm that generates free energy for life. Over the $\sim$4 Gyr history of Earth, the total energy incident at the top of the atmosphere and within the biological available window is $\sim$10$^{34}$ J. The hypothesis assumes that the rate of evolution from the origin of life to complex life is proportional to this total energy, which would suggest that planets orbiting other stars should not show signs of complex life if the total energy incident on the planet is below this energy threshold. The proportional evolutionary time hypothesis predicts that late K- and M-dwarf stars (M < 0.7 M$_{\odot}$) are too young to host any complex life at the present age of the universe. F-, G-, and early K-dwarf stars (M > 0.7 M$_{\odot}$) represent the best targets for the next generation of space telescopes to search for spectroscopic biosignatures indicative of complex life.
1905.07410
Cosmic inference: constraining parameters with observations and highly limited number of simulations
Takhtaganov, et al
Cosmological probes pose an inverse problem where the measurement result is obtained through observations, and the objective is to infer values of model parameters which characterize the underlying physical system -- our Universe. Modern cosmological probes increasingly rely on measurements of the small-scale structure, and the only way to accurately model physical behavior on those scales, roughly 65 Mpc/h or smaller, is via expensive numerical simulations. In this paper, we provide a detailed description of a novel statistical framework for obtaining accurate parameter constraints by combining observations with a very limited number of cosmological simulations. The proposed framework utilizes multi-output Gaussian process emulators that are adaptively constructed using Bayesian optimization methods. We compare several approaches for constructing multi-output emulators that enable us to take possible inter-output correlations into account while maintaining the efficiency needed for inference. Using Lyman alpha forest flux power spectrum, we demonstrate that our adaptive approach requires considerably fewer --- by a factor of a few in Lyman alpha P(k) case considered here --- simulations compared to the emulation based on Latin hypercube sampling, and that the method is more robust in reconstructing parameters and their Bayesian credible intervals.
1905.07557
Testing halo assembly bias using galaxy clusters
Sunayama, More
We critically examine the methodology behind the claimed observational detection of halo assembly bias using optically selected galaxy clusters by Miyatake et al. (2016) and More et al. (2016). We mimic the optical cluster detection algorithm and apply it to two different mock catalogs generated from the Millennium simulation galaxy catalog, one in which halo assembly bias signal is present, while the other in which the assembly bias signal has been expressly erased. We split each of these cluster samples into two using the average cluster-centric distance of the member galaxies to measure the difference in the clustering strength of the subsamples with respect to each other. We observe that the subsamples split by cluster-centric radii show differences in clustering strength, even in the catalog where the true assembly bias signal was erased. We show that this is a result of contamination of the member galaxy sample from interlopers along the line-of-sight. This undoubtedly shows that the particular methodology adopted in the previous studies cannot be used to claim a detection of the assembly bias signal. We figure out the tell-tale signatures of such contamination, and show that the observational data also shows similar signatures. Furthermore, we also show that projection effects in optical galaxy clusters can bias the inference of the 3-dimensional edges of galaxy clusters (splashback radius), so appropriate care should be taken while interpreting the splashback radius of optical clusters.
1905.07803
The matter fluctuation amplitude inferred from the weak lensing power spectrum and correlation function in CHFTLenS data
Lu, Haiman
Based on the cosmic shear data from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS), Kilbinger et al. (2013) obtained a constraint on the amplitude of matter fluctuations of $\sigma_8({\Omega_\mathrm{m}}/0.27)^{0.6}=0.79\pm0.03$ from the two-point correlation function (2PCF). This is $\approx3\sigma$ lower than the value $0.89\pm0.01$ derived from Planck data on cosmic microwave background (CMB) anisotropies. On the other hand, based on the same CFHTLenS data, but using the power spectrum, and performing a different analysis, Liu et al. (2015) obtained the higher value of $\sigma_8({\Omega_\mathrm{m}}/0.27)^{0.64}=0.87^{+0.05}_{-0.06}$. We here investigate the origin of this difference, by performing a fair side-by-side comparison of the 2PCF and power spectrum analyses on CFHTLenS data. We find that these two statistics indeed deliver different results, even when applied to the same data in an otherwise identical procedure. We identify excess power in the data on small scales ($\ell>5,000$) driving the larger values inferred from the power spectrum. We speculate on the possible origin of this excess small-scale power.
1905.08017
Occurrence of great magnetic storms on 6-8 March 1582
Hattori, Hayakawa, Ebihara
Although knowing the occurrence frequency of severe space weather events is important for a modern society, it is insufficiently known due to the lack of magnetic or sunspot observations, before the Carrington event in 1859 known as one of the largest events during the last two centuries. Here, we show that a severe magnetic storm occurred on 8 March 1582 based on auroral records in East Asia. The equatorward boundary of auroral visibility reached 28.8{\deg} magnetic latitude. The equatorward boundary of the auroral oval is estimated to be 33.0{\deg} invariant latitude (ILAT), which is comparable to the storms on 25/26 September 1909 (~31.6{\deg} ILAT, minimum Dst of -595 nT), 28/29 August 1859 (~36.5{\deg} ILAT), and 13/14 March 1989 (~40{\deg} ILAT, minimum Dst of -589 nT). Assuming that the equatorward boundary is a proxy for the scale of magnetic storms, we presume that the storm on March 1582 was severe. We also found that the storm on March 1582 lasted, at least, for three days by combining European records. The auroral oval stayed at mid-latitude for the first two days and moved to low-latitude (in East Asia) for the last day. It is plausible that the storm was caused by a series of ICMEs (interplanetary coronal mass ejections). We can reasonably speculate that a first ICME could have cleaned up interplanetary space to make the following ICMEs more geo-effective, as probably occurred in the Carrington and Halloween storms.
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