1807.06664
SOFIA/HAWC+ detection of a gravitationally lensed starburst galaxy at $z$=1.03
Ma, et al
Present the detection at 89 um (observed frame) of the Herschel-Selected gravitationally lensed starburst galaxy HATLASJ1429-0028 (also know as G15v2.19) in 15 minutes with the High-resolution Airborne Wideband Camera-plus (HAWC+) onboard SOFIA. The spectacular lensing system consists of an edge-on foreground disk galaxy at z=0.22 and a nearly complete Einstein ring of an intrinsic ultra-luminous infrared galaxy at z=1.03. Is this high IR luminosity powered by pure SF or also an AGN? Previous nebular line diagnostics indicate that it is SF dominated. Perform a 27-band multi-wavelength SED including the new SOFIA/HAWC+ data to constrain the fractional AGN contribution to the total IR luminosity. The AGN fraction in the IR turns out to be negligible. In addition, J1429-0028 serves as a testbed for comparing SED results from different models/templates and SED codes (MAGPHYS, SED3FIT, and CIGALE). Stress that SFH is the dominant source of uncertainty in the derived M* (as high as a factor of ~10) even in the case of extensive photometric coverage. Furthermore, the detection of a source at z~1 with SOFIA/HAWC+ demonstrates the potential of utilizing this facility for distant galaxy studies including the decomposition of SF/AGN components, which cannot be accomplished with other current facilities.
1807.06870
Detecting domain walls in laboratory experiments
Llinares, Brax
The inherently unstable nature of domain walls makes their detection in laboratory experiments extremely challenging. Propose a method to stabilize domain walls in a particular modified gravity model inside a cavity. Suggest 2 ways in which the walls could be detected once stabilized: studying the trajectories of Ultra Cold Neutrons (UCN's) either via the defection angle of a neutron beam induced by the attraction towards the wall or through the time difference of these particles passing through the wall. Give realistic estimates for these effects and expect that they should be detectable experimentally.
1807.06875
A Bayesian method for combining theoretical and simulated covariance matrices for large-scale structure surveys
Hall, Taylor
Accurate and precise covariance matrices will be important in enabling planned cosmological surveys to detect new physics. Standard methods imply either the need for many N-body sims in order to obtain an accurate estimate, or a precise theoretical model. Combine these approaches by constructing a likelihood function conditions on simulated and theoretical covariances, consistently propagating noise from the finite number of simulations and uncertainty in the theoretical model itself using an informative Invers-Wishart prior. Unlike standard methods, the approach allows the required number of simulations to be less than the number of summary statistics. Recover the linear 'shrinkage' covariance estimator in the context of a Beysian data model, and test the marginal likelihood on simulated mock power spectrum estimates. Conduct a thorough investigation into the impact of prior confidence in different choices of covariance models on the quality of model fits and parameter variances. In a simplified setting find that the number of simulations required can be reduced if one is willing to accept a mild degradation in the quality of model fits, finding that even weakly informative priors can help to reduce the simulation requirements. Identify the correlation matrix of the summary statistics as a key quantity requiring careful modeling. The approach can be easily generalized to any covariance model or set of summary statistics, and elucidates the role of hybrid estimators in cosmological inference.
1807.07084
A quantification of the butterfly effect in cosmological simulations and implications for galaxy scaling relations
Genel, et al
Study the chaotic-like behavior of cosmo sims by quantifying how minute perturbations grow over time and manifest as macroscopic differences in galaxy properties. When the same setup is run multiple times, the results produced by the code Arepo, are binary identical. However, when pairs of 'shadow' simulations are run that are identical except for random minute initial displacements to particle positions (e.g. of order 1e-7 pc), the results diverge from each other at the individual galaxy level (while the statistical properties of the ensemble of galaxies are unchanged). After cosmological times, the global properties of pairs of 'shadow' galaxies that are matched between the simulations differ from each other generally at a level of ~2-25%, depending on the considered physical quantity. Perform these experiments using cosmo volumes of (25-50 Mpc/h)^3 evolved either purely with DM, or with baryons and SF but no feedback, or using the full feedback model of the IllustrisTNG project. The runs cover 4 resolution levels spanning a factor of 512 in mass. Find that without feedback the differences between shadow galaxies generally become smaller as the resolution increases, but with the IllustrisTNG model the results are mostly covering towards a 'floor'. This hints at the role of feedback in setting the chaotic properties of galaxy formation. Importantly, compare the macroscopic differences between shadow galaxies to the overall scatter in various galaxy scaling relations, and conclude that for the star formation-mass and the Tully-Fisher relations, the chaotic behavior of the simulations contributes significantly to the overall scatter. Discuss the implications for galaxy formation theory in general and for cosmological simulations in particular.
1807.07435
A multi messenger view of galaxies and quasars from now to mid-century
D'Onofrio, Marziani
I the next 30 years, a new generation of space and ground-based telescopes will permit to obtain multi-frequency observations of faint sources and, for the first time in human history, to achieve a deep, almost synoptical monitoring of the whole sky. Gravitational wave observatories will detect a Universe of unseen BHs in the merging process over a broad spectrum of mass. Computing facilities will permit new high-resolution simulations with a deeper physical analysis of the main phenomena occurring at different scales. Given these development lines, first sketch a panorama of the main instrumental developments expected in the next 30 years, dealing not only with EM radiation, but also from a multi-messenger perspective that includes GWs, neutrinos, and CRs. Then present how the new instrumentation will make it possible to foster advances in the present understanding of galaxies and quasars. Focus on selected scientific themes that are hotly debated today, in some cases advancing conjectures on the solution of major problems that may become solved in the next 30 years.
1807.07548
The maximum angular-diameter distance in cosmology
Melia, Yennapureddy
Unlike other observational signatures in cosmology, the angular-diameter distance d_A(z) uniquely reaches a maximum (at z_max) and then shrinks to zero towards the big bang. The location of this turning point depends sensitively on the model, but has been difficult to measure. In this paper, estimate and use z_max inferred from quasar cores: (1) by employing a sample of 140 objects yielding a much reduced dispersion due to pre-constrained limits on their spectral index and luminosity, (2) by reconstructing d_A(z) using Gaussian processes, and (3) comparing the predictions of 7 different cosmologies and showing that the measured value of z_max can effectively discriminate between them. Find that z_max=1.70±0.20 --- an important new probe of the Universe's geometry. The most strongly favored model is R_h=ct, followed by Planck LCDM. Several others, including Milne, Einstein-de Sitter and Static tired light are stonily rejected. According to these results, the R_h=ct universe, which predicts z_max=1.718, has a ~92.8% probability of being the correct cosmology. For consistency, also carry out model selection based on d_A(z) itself. This test confirms that R_h=ct and Planck LCDM are among the few models that account for angular-size data better than those that are disfavored by z_max. The d_A(z) comparison, however, is less discerning than that with z_max, due to the additional free parameter, H_0. Find that H_0=63.4±1.2 km/s/Mpc for R_h=ct, and 69.9±1.5 km/s/Mpc for LCDM. Both are consistent with previously measured values in each model, though they differ from each other by over 4 sigma. In contrast, model selection based on z_max is independent of H0.
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