Day 1580

Wednesday.

1906.00968
Exploring the effects of galaxy formation on matter clustering through a library of simulation power spectra
van Daalen, et al

Upcoming weak lensing surveys require a detailed theoretical understanding of the matter power spectrum in order to derive accurate and precise cosmological parameter values. While galaxy formation is known to play an important role, its precise effects are currently unknown. We present a set of 92 matter power spectra from the OWLS, cosmo-OWLS and BAHAMAS simulation suites, including different $\Lambda$CDM cosmologies, neutrino masses, subgrid prescriptions and AGN feedback strengths. We conduct a detailed investigation of the dependence of the relative difference between the total matter power spectra in hydrodynamical and collisionless simulations on the effectiveness of stellar and AGN feedback, cosmology and redshift. The strength of AGN feedback can greatly affect the power on a range of scales, while a lack of stellar feedback can greatly increase the effectiveness of AGN feedback on large scales. We also examine differences in the initial conditions of hydrodynamic and N-body simulations that can lead to a ~1% discrepancy in the large-scale power, and furthermore show our results to be insensitive to cosmic variance. We present an empirical model capable of predicting the effect of galaxy formation on the matter power spectrum at z=0 to within 1% for k<1 h/Mpc, given only the mean baryon fraction in galaxy groups. Differences in group baryon fractions can also explain the quantitative disagreement between predictions from the literature. All total and dark matter only power spectra in this library will be made publicly available at powerlib.strw.leidenuniv.nl.

1906.00975

on the mass mitmatch between simulations and weak-lensing measurements

Svensmark, et al

The recently discovered discrepancy between galaxy mass measurements from weak lensing and predictions from abundance matching questions our understanding of cosmology, or of the galaxy-halo connection, or of both. We re-examined this tension by considering, as models, different cosmological simulations in the Illustris suite. We produced excess profiles $R\Delta\Sigma$ from subhalo snapshots at different redshifts in Illustris-1 and IllustrisTNG (TNG100 and TNG300) simulations, enabling a direct comparison with weak-lensing measurements. We separate the individual contributions of stars, dark matter and gas within $\approx1$ Mpc (comoving length), beyond which correlated two-halo terms dominate. The mismatch between measurements and predictions is more severe than in previous studies: $R\Delta\Sigma$ profiles from IllustrisTNG are $\approx2$ times higher than the measured ones. Contrary to abundance matching results, the mismatch is mostly unchanged with increasing redshifts. The contribution of gas to the $R\Delta\Sigma$ profiles is $5-10\%$ over the scales dominated by one-halo terms. Different procedures to link stellar and halo masses (abundance matching, cosmological simulations) are still significantly discrepant with weak lensing measurements, but their trends are different. Therefore, the change in cosmological parameters advocated through abundance-matching arguments may not resolve this tension. Also, current criteria to select isolated massive galaxies in simulations are susceptible to resolution issues and may not correspond to observational criteria. The (currently subdominant) contribution of gas is non-negligible, and even if the major discrepancy within stellar and halo masses is resolved, it will be an appreciable source of systematics in the LSST era, when uncertainties on the $R\Delta\Sigma$ profiles are expected to be $\approx10$ times smaller.

1906.01018

Monte Carlo control loops for cosmic shear cosmology with DES year 1

Kacprzak, et al

Weak lensing by large-scale structure is a powerful probe of cosmology and of the dark universe. This cosmic shear technique relies on the accurate measurement of the shapes and redshifts of background galaxies and requires precise control of systematic errors. The Monte Carlo Control Loops (MCCL) is a forward modelling method designed to tackle this problem. It relies on the Ultra Fast Image Generator (UFig) to produce simulated images tuned to match the target data statistically, followed by calibrations and tolerance loops. We present the first end-to-end application of this method, on the Dark Energy Survey (DES) Year 1 wide field imaging data. We simultaneously measure the shear power spectrum $C_{\ell}$ and the redshift distribution $n(z)$ of the background galaxy sample. The method includes maps of the systematic sources, Point Spread Function (PSF), an Approximate Bayesian Computation (ABC) inference of the simulation model parameters, a shear calibration scheme, and the fast estimation of the covariance matrix. We find a close statistical agreement between the simulations and the DES Y1 data using an array of diagnostics. In a non-tomographic setting, we derive a set of $C_\ell$ and $n(z)$ curves that encode the cosmic shear measurement, as well as the systematic uncertainty. Following a blinding scheme, we measure the combination of $\Omega_m$, $\sigma_8$, and intrinsic alignment amplitude $A_{\rm{IA}}$, defined as $S_8D_{\rm{IA}} = \sigma_8(\Omega_m/0.3)^{0.5}D_{\rm{IA}}$, where $D_{\rm{IA}}=1-0.11(A_{\rm{IA}}-1)$. We find $S_8D_{\rm{IA}}=0.895^{+0.054}_{-0.039}$, where systematics are at the level of roughly 60\% of the statistical errors. We discuss these results in the context of earlier cosmic shear analyses of the DES Y1 data. Our findings indicate that this method and its fast runtime offer good prospects for cosmic shear measurements with future wide-field surveys.

1906.01382

The essential elements of dust evolution: a viable solution to the interstellar oxygen depletion problem?

Jones, Ysrad

There remain many open questions relating to the depletion of elements into dust, e.g., exactly how are C and O incorporated into dust in dense clouds and, in particular, what drives the disappearance of oxygen in the denser interstellar medium? This work is, in part, an attempt to explain the apparently anomalous incorporation of O atoms into dust in dense clouds. We re-visit the question of the depletion of the elements incorporated into the carbonaceous component of interstellar dust, i.e., C, H, O, N and S, in the light of recent analyses of the organics in comets, meteorites and interplanetary dust particles. We find that oxygen could be combined with ~ 10 to 20 % of the carbon in the dust in dense regions in the form of a difficult to observe, organic carbonate, which could explain the unaccounted for 170-255 ppm oxygen depletion. We conclude that, while C, O and N atoms are depleted into an amorphous a-C:H:O:N phase, we posit that a significant fraction of C and O atoms could be sequestered into an organic carbonate, which provides a viable solution to the oxygen depletion problem. Further, the thermal or photolytic decomposition of this carbonate may have a bearing on the formation of CO_2 in the ISM.

1906.01443

Fluctuation of the background sky in the Hubble Extremely Deep Field (XDF) and its origin

Matsumoto, Tsumura

We performed a fluctuation analysis of the Hubble Extremely Deep Field (XDF) at four optical wavelength bands and found large fluctuations that are significantly brighter than those expected for ordinary galaxies. Good cross-correlations with flat spectra are found down to 0.2 arcsec, indicating the existence of a spatial structure even at the 0.2 arcsec scale. The detected auto and cross-correlations provide a lower limit of 24 nW m$^{-2}$ sr$^{-1}$ for the absolute sky brightness at 700-900 nm, which is consistent with previous observations. We searched for candidate objects to explain the detected large fluctuation using the catalog of the Hubble Ultra Deep Field (UDF), and found that the surface number density of faint compact objects (FCOs) rapidly increases toward the faint end. Radial profiles of FCOs are indistinguishable from the PSF, and the effective radius based on de Vaucouleur's law is estimated to be smaller than 0.02 arcsec. The SEDs of FCOs follow a power law at optical wavelengths, but show greater emission and structure at $\lambda$ > 1 $\mu$m. Assuming that the FCOs are the cause of the excess brightness and fluctuations, the faint magnitude limit is 34.9 mag for the F775W band, and the surface number density reaches $2.6 \times 10^3$ (arcsec)$^{-2}$. Recent gamma-ray observations require that the redshift of FCOs must be less than 0.1, if FCOs are the origin of the excess optical and infrared background. Assuming that FCOs consist of missing baryons, the mass and luminosity of a single FCO range from $10^{2}$ to 1$0^{3}$ solar units, and mass-to-luminosity ratio is significantly lower than 1.0 solar unit. The maximum effective radius of an FCO is 4.7 pc. These results and the good correlation between near-infrared and X-ray background indicate that FCOs could be powered by the gravitational energy associated with black holes.

1906.01623

And yet it flips: connecting galactic spin and the cosmic web

Kraljic, et al

We study the spin alignment of galaxies and halos with respect to filaments and walls of the cosmic web, identified with DisPerSE, using the SIMBA simulation from z=0-2. Massive halos' spins are oriented perpendicularly to their closest filament's axis and walls, while low mass halos tend to have their spins parallel to filaments and in the plane of walls. A similar mass-dependent spin flip is found for galaxies, albeit with a weaker signal particularly at low mass and low-z, suggesting that galaxies' spins retain memory of their larger-scale environment. Low-z star-forming and rotation-dominated galaxies tend to have spins parallel to nearby filaments, while quiescent and dispersion-dominated galaxies show preferentially perpendicular orientation; the star formation trend can be fully explained by the stellar mass correlation, but the morphology trend cannot. There is a strong dependence on HI mass, such that high-HI galaxies tend to have parallel spins while low-HI galaxies are perpendicular, which persists even when matching samples in stellar mass, suggesting that HI content traces anisotropic infall more faithfully than the stellar component. Finally, at fixed stellar mass, the strength of spin alignments correlates with the filament's density, with parallel alignment for galaxies in high density environments. These findings are consistent with conditional tidal torque theory, and highlight a significant correlation between galactic spin and the larger scale tides that are important e.g. for interpreting weak lensing studies. SIMBA allows us to rule out numerical grid locking as the cause of previously-seen low mass alignment.