1912.09481
A synthetic WFIRST high-latitude imaging survey: simulation suite and the impact of wavefronts errors on weak gravitational lensing
Troxel, et al
The Wide-Field InfraRed Survey Telescope (WFIRST) mission is expected to launch in the mid-2020s. Its weak lensing program is designed to enable unprecedented systematics control in photometric measurements, including shear recovery, point-spread function (PSF) correction, and photometric calibration. This will enable exquisite weak lensing science and allow us to adjust to and reliably contribute to the cosmological landscape after the initial years of observations from other concurrent Stage IV dark energy experiments. This potential requires equally careful planning and requirements validation as the mission prepares to enter its construction phase. We present a suite of image simulations based on GalSim that are used to construct a complex, synthetic WFIRST weak lensing survey that incorporates realistic input galaxies and stars, relevant detector non-idealities, and the current reference five-year WFIRST survey strategy. We present a first study to empirically validate the existing WFIRST weak lensing requirements flowdown using a suite of 12 matched image simulations, each representing a different perturbation to the wavefront or image motion model. These are chosen to induce a range of potential static and low- and high-frequency time-dependent PSF model errors. We analyze the measured shapes of galaxies from each of these simulations and compare them to a reference, fiducial simulation to infer the response of the shape measurement to each of these modes in the wavefront model. We then compare this to existing analytic flowdown requirements, and find general agreement between the empirically derived response and that predicted by the analytic model.
A synthetic WFIRST high-latitude imaging survey: simulation suite and the impact of wavefronts errors on weak gravitational lensing
Troxel, et al
The Wide-Field InfraRed Survey Telescope (WFIRST) mission is expected to launch in the mid-2020s. Its weak lensing program is designed to enable unprecedented systematics control in photometric measurements, including shear recovery, point-spread function (PSF) correction, and photometric calibration. This will enable exquisite weak lensing science and allow us to adjust to and reliably contribute to the cosmological landscape after the initial years of observations from other concurrent Stage IV dark energy experiments. This potential requires equally careful planning and requirements validation as the mission prepares to enter its construction phase. We present a suite of image simulations based on GalSim that are used to construct a complex, synthetic WFIRST weak lensing survey that incorporates realistic input galaxies and stars, relevant detector non-idealities, and the current reference five-year WFIRST survey strategy. We present a first study to empirically validate the existing WFIRST weak lensing requirements flowdown using a suite of 12 matched image simulations, each representing a different perturbation to the wavefront or image motion model. These are chosen to induce a range of potential static and low- and high-frequency time-dependent PSF model errors. We analyze the measured shapes of galaxies from each of these simulations and compare them to a reference, fiducial simulation to infer the response of the shape measurement to each of these modes in the wavefront model. We then compare this to existing analytic flowdown requirements, and find general agreement between the empirically derived response and that predicted by the analytic model.
1912.11647
The impact of filamentary accretion of sub haloes on the shape and orientation of haloes
Morinaga, Ishiyama
Dark matter haloes are formed through hierarchical mergers of smaller haloes in large-scale cosmic environments, and thus anisotropic subhalo accretion through cosmic filaments have some impacts on halo structures. Recent studies using cosmological simulations have shown that the orientations of haloes correlate with the direction of cosmic filaments, and these correlations significantly depend on the halo mass. Using high-resolution cosmological $N$-body simulations, we quantified the strength of filamentary subhalo accretion for galaxy- and group-sized host haloes ($M_{\rm host}=5\times10^{11-13}M_{\odot}$) by regarding the entry points of subhaloes as filaments and present statistical studies that how the shape and orientation of host haloes at redshift zero correlate with the strength of filamentary subhalo accretion. We confirm previous studies that found the host halo mass dependence of the alignment between orientations of haloes and filaments. We also show that, for the first time, the shape and orientation of haloes weakly correlate with the strength of filamentary subhalo accretion even if the halo masses are the same. Minor-to-major axis ratios of haloes tend to decrease as their filamentary accretion gets stronger. Haloes with highly anisotropic accretion become more spherical or oblate, while haloes with isotropic accretion become more prolate or triaxial. For haloes with strong filamentary accretion, their major axes are preferentially aligned with the filaments, while their angular momentum vectors tend to be slightly more misaligned.
1912.11935
Secular extragalactic parallax: measurement methods and predictions for Gaia
Paine, et al
Secular extragalactic parallax caused by the solar system's velocity relative to the cosmic microwave background rest frame may be observable as a dipole proper motion field with amplitude $78~\mu$as yr$^{-1}$ Mpc. Nearby galaxies also exhibit proper motions caused by their transverse peculiar velocities that prevent detection of secular parallax for any single galaxy, although a statistical detection may be made instead. Such a detection could constrain the local Hubble parameter. We present methods to measure secular parallax using correlated extragalactic proper motions and find a first limit on the secular parallax amplitude using proper motions of 232 nearby galaxies from Gaia Data Release 2. The recovered dipole has insignificant upper limit of 3500 $\mu$as yr$^{-1}$ Mpc. This measurement will be improved by larger sample size and reduced proper motion uncertainties in future data releases. Using the local peculiar velocity field derived from Cosmicflows-3, we simulate galaxy proper motions and predict that a significant detection ($5-10\sigma$) of the secular parallax amplitude will be possible by Gaia's end of mission. The detection is contingent on proper motions of nearby ($<5$ Mpc), bright ($G<15$ mag) galaxies, and corresponds to an insignificant upper limit on the Hubble parameter. We further investigate the implications of our simulations for the study of transverse peculiar velocities, which we find to be consistent with large scale structure theory. The peculiar velocity field additionally results in low-multipole correlated proper motions on the order of $0.3~\mu$as yr$^{-1}$ that may be confounded with other cosmological proper motion measurements, such as limits on the gravitational wave background and the anisotropy of the Hubble expansion.
1912.11935
Secular extragalactic parallax: measurement methods and predictions for Gaia
Paine, et al
Secular extragalactic parallax caused by the solar system's velocity relative to the cosmic microwave background rest frame may be observable as a dipole proper motion field with amplitude $78~\mu$as yr$^{-1}$ Mpc. Nearby galaxies also exhibit proper motions caused by their transverse peculiar velocities that prevent detection of secular parallax for any single galaxy, although a statistical detection may be made instead. Such a detection could constrain the local Hubble parameter. We present methods to measure secular parallax using correlated extragalactic proper motions and find a first limit on the secular parallax amplitude using proper motions of 232 nearby galaxies from Gaia Data Release 2. The recovered dipole has insignificant upper limit of 3500 $\mu$as yr$^{-1}$ Mpc. This measurement will be improved by larger sample size and reduced proper motion uncertainties in future data releases. Using the local peculiar velocity field derived from Cosmicflows-3, we simulate galaxy proper motions and predict that a significant detection ($5-10\sigma$) of the secular parallax amplitude will be possible by Gaia's end of mission. The detection is contingent on proper motions of nearby ($<5$ Mpc), bright ($G<15$ mag) galaxies, and corresponds to an insignificant upper limit on the Hubble parameter. We further investigate the implications of our simulations for the study of transverse peculiar velocities, which we find to be consistent with large scale structure theory. The peculiar velocity field additionally results in low-multipole correlated proper motions on the order of $0.3~\mu$as yr$^{-1}$ that may be confounded with other cosmological proper motion measurements, such as limits on the gravitational wave background and the anisotropy of the Hubble expansion.
1912.12269
Calculation of distances in cosmological models with small-scale inhomogeneities and their use in observational cosmology: a review
Helbig
The Universe is not completely homogeneous. Even if it is sufficiently so on large scales, it is very inhomogeneous at small scales, and this has an effect on light propagation, so that the distance as a function of redshift, which in many cases is defined via light propagation, can differ from the homogeneous case. Simple models can take this into account. I review the history of this idea, its generalization to a wide variety of cosmological models, analytic solutions of simple models, comparison of such solutions with exact solutions and numerical simulations, applications, simpler analytic approximations to the distance equations, and (for all of these aspects) the related concept of a "Swiss-cheese" universe.
1912.12278
Modified initial power spectrum and too big to fail problem
Kameli, Baghram
The galactic scale challenges of dark matter such as "missing satellite" problem and "too big to fail" problem is one of the main caveats of standard model of cosmology. These challenges can be solved either by implementing the complicated baryonic physics or it could be an indication to a new physics beyond the standard model of cosmology. The modification of collision less dark matter models or modification of standard initial conditions are two promising venues for study. In this work, we investigate the effects of the deviations from scale invariant initial curvature power spectrum on number density of dark matter halos. In this work we develop the non-Markov extension of the excursion set theory to address the number density count of dark matter substructures and dark matter halo progenitor mass distribution. We show that the plausible solution to "too big to fail" problem could obtain by a Gaussian excess in initial power in the scales of $k_* \sim 3 h/Mpc$ which is related to the mass scale of $M_* \sim 10^{11} M_{\odot}$. We show that this deviation is consistent with the current status of the non-linear power spectrum. Our proposal also has a prediction that the number density of Milky way type galaxies must be higher than the standard case.
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