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The High-Latitude Survey of the Nancy Grace Roman Space Telescope is expected to measure the positions and shapes of hundreds of millions of galaxies in an area of 2220 deg2. This survey will provide high-quality weak lensing data with unprecedented systematic control. The Roman Space Telescope will survey the sky in near-infrared (NIR) bands using Teledyne H4RG HgCdTe photodiode arrays. These NIR arrays exhibit an effect called persistence: charges that are trapped in the photodiodes during earlier exposures are gradually released into later exposures, leading to contamination of the images and potentially to errors in measured galaxy properties such as fluxes and shapes. In this work, we use image simulations that incorporate the persistence effect to study its impact on galaxy shape measurements and weak lensing signals. No significant spatial correlations are found between the galaxy shape changes induced by persistence. On the scales of interest for weak lensing cosmology, the effect of persistence on the weak lensing correlation function is about two orders of magnitude lower than the Roman Space Telescope additive shear error budget, indicating that the persistence effect is expected to be a subdominant contributor to the systematic error budget for weak lensing with the Roman Space Telescope given its current design. [ABSTRACT FROM AUTHOR]

The Wide Field Infrared Survey Telescope (WFIRST) will conduct a galaxy redshift survey using the H α emission line primarily for spectroscopic redshift determination. Due to the modest spectroscopic resolution of the grism, the H α and the neighbouring [N  ii ] lines are blended, leading to a redshift bias that depends on the [N  ii ]/H α ratio, which is correlated with a galaxy's metallicity, hence mass and ultimately environment. We investigate how this bias propagates into the galaxy clustering and cosmological parameters obtained from the WFIRST. Using simulation, we explore the effect of line blending on redshift-space distortion and baryon acoustic oscillation (BAO) measurements. We measure the BAO parameters α ∥, α ⊥, the logarithmic growth factor f |$v$| , and calculate their errors based on the correlations between the line ratio and large-scale structure. We find |$\Delta \alpha _{\parallel } = 0.31 \pm 0.23 {{\ \rm per\ cent}}$| (⁠|$0.26\pm 0.17{{\ \rm per\ cent}}$|⁠), |$\Delta \alpha _{\perp } = -0.10\pm 0.10{{\ \rm per\ cent}}$| (⁠|$-0.12 \pm 0.11 {{\ \rm per\ cent}}$|⁠), and |$\Delta f_{v} = 0.17\pm 0.33{{\ \rm per\ cent}}$| (⁠|$-0.20 \pm 0.30{{\ \rm per\ cent}}$|⁠) for redshift 1.355–1.994 (0.700–1.345), which use approximately 18  |${{\ \rm per\ cent}}$|⁠, 9  |${{\ \rm per\ cent}}$|⁠, and 7  |${{\ \rm per\ cent}}$| of the systematic error budget in a root-sum-square sense. These errors may already be tolerable but further mitigations are discussed. Biases due to the environment-independent redshift error can be mitigated by measuring the redshift error probability distribution function. High-spectral-resolution reobservation of a few thousand galaxies would be required (if by direct approach) to reduce them to below 25  |${{\ \rm per\ cent}}$| of the error budget. Finally, we outline the next steps to improve the modelling of [N  ii ]-induced blending biases and their interaction with other redshift error sources. [ABSTRACT FROM AUTHOR]

The baryon-acoustic oscillation (BAO) feature in the Lyman-α forest is a key probe of the cosmic expansion rate at redshifts ɀ ~ 2.5, well before dark energy is believed to have become significant. A key advantage of the BAO as a standard ruler is that it is a sharp feature and hence is more robust against broad-band systematic effects than other cosmological probes. However, if the Lyman-α forest transmission is sensitive to the initial streaming velocity of the baryons relative to the dark matter, then the BAO peak position can be shifted. Here we investigate this sensitivity using a suite of hydrodynamic simulations of small regions of the intergalactic medium with a range of box sizes and physics assumptions; each simulation starts from initial conditions at the kinematic decoupling era (ɀ ~ 1059), undergoes a discrete change from neutral gas to ionized gas thermal evolution at reionization (ɀ ~ 8), and is finally processed into a Lyman-α forest transmitted flux cube. Streaming velocities suppress small-scale structure, leading to less violent relaxation after reionization. The changes in the gas distribution and temperature-density relation at low redshift are more subtle, due to the convergent temperature evolution in the ionized phase. The change in the BAO scale is estimated to be of the order of 0.12 per cent at ɀ = 2.5; some of the major uncertainties and avenues for future improvement are discussed. The predicted streaming velocity shift would be a subdominant but not negligible effect (of order 0.26σ) for the upcoming DESI Lyman-α forest survey, and exceeds the cosmic variance floor. [ABSTRACT FROM AUTHOR]

Redshifted H?I 21 cm emission from unresolved low-redshift large-scale structure is a promising window for ground-based baryon acoustic oscillations (BAO) observations. A major challenge for this method is separating the cosmic signal from the foregrounds of Galactic and extra-Galactic origins that are stronger by many orders of magnitude than the former. The smooth frequency spectrum expected for the foregrounds would nominally contaminate only very small k? modes; however, the chromatic response of the telescope antenna pattern at this wavelength to the foreground introduces non-smooth structure, pervasively contaminating the cosmic signal over the physical scales of our interest. Such contamination defines a wedged volume in Fourier space around the transverse modes that is inaccessible for the cosmic signal. In this paper, we test the effect of this contaminated wedge on the future 21-cm BAO surveys using Fisher information matrix calculation. We include the signal improvement due to the BAO reconstruction technique that has been used for galaxy surveys and test the effect of this wedge on the BAO reconstruction as a function of signal to noises and incorporate the results in the Fisher matrix calculation. We find that the wedge effect expected at z = 1-2 is very detrimental to the angular diameter distances: the errors on angular diameter distances increased by 3-4.4 times, while the errors on H(z) increased by a factor of 1.5-1.6. We conclude that calibration techniques that clean out the foreground 'wedge' would be extremely valuable for constraining angular diameter distances from intensity-mapping 21-cm surveys. [ABSTRACT FROM AUTHOR]

ABSTRACT In astrophysical regimes where the collisional excitation of hydrogen atoms is relevant, the cross-sections for the interactions of hydrogen atoms with electrons and protons are necessary for calculating line profiles and intensities. In particular, at relative velocities exceeding ∼1000 km s−1, collisional excitation by protons dominates over that by electrons. Surprisingly, the H-H+ cross-sections at these velocities do not exist for atomic levels of n≥ 4, forcing researchers to utilize extrapolation via inaccurate scaling laws. In this study, we present a faster and improved algorithm for computing cross-sections for the H-H+ collisional system, including excitation and charge transfer to the n≥ 2 levels of the hydrogen atom. We develop a code named bdscx which directly solves the Schrödinger equation with variable (but non-adaptive) resolution and utilizes a hybrid spatial-Fourier grid. Our novel hybrid grid reduces the number of grid points needed from ∼4000 n6 (for a 'brute force', Cartesian grid) to ∼2000 n4 and speeds up the computation by a factor of ∼50 for calculations going up to n= 4. We present ( l, m)-resolved results for charge transfer and excitation final states for n= 2-4 and for projectile energies of 5-80 keV, as well as fitting functions for the cross-sections. The ability to accurately compute H-H+ cross-sections to n= 4 allows us to calculate the Balmer decrement, the ratio of Hα to Hβ line intensities. We find that the Balmer decrement starts to increase beyond its largely constant value of 2-3 below 10 keV, reaching values of 4-5 at 5 keV, thus complicating its use as a diagnostic of dust extinction when fast (∼1000 km s−1) shocks are impinging upon the ambient interstellar medium. [ABSTRACT FROM AUTHOR]

ABSTRACT Current and upcoming wide-field, ground-based, broad-band imaging surveys promise to address a wide range of outstanding problems in galaxy formation and cosmology. Several such uses of ground-based data, especially weak gravitational lensing, require highly precise measurements of galaxy image statistics with careful correction for the effects of the point spread function (PSF). In this paper, we introduce the shera (SHEar Reconvolution Analysis) software to simulate ground-based imaging data with realistic galaxy morphologies and observing conditions, starting from space-based data (from the Cosmological Evolution Survey, COSMOS) and accounting for the effects of the space-based PSF. This code simulates ground-based data, optionally with a weak lensing shear applied, in a model-independent way using a general Fourier space formalism. The utility of this pipeline is that it allows for a precise, realistic assessment of systematic errors due to the method of data processing, for example in extracting weak lensing galaxy shape measurements or galaxy radial profiles, given user-supplied observational conditions and real galaxy morphologies. Moreover, the simulations allow for the empirical test of error estimates and determination of parameter degeneracies, via generation of many noise maps. The public release of this software, along with a large sample of cleaned COSMOS galaxy images (corrected for charge transfer inefficiency), should enable upcoming ground-based imaging surveys to achieve their potential in the areas of precision weak lensing analysis, galaxy profile measurement and other applications involving detailed image analysis. [ABSTRACT FROM AUTHOR]

We investigate the rotational emission from dust grains that rotate around non-principal axes. We argue that in many phases of the interstellar medium, the smallest grains, which dominate spinning dust emission, are likely to have their nutation state (orientation of principal axes relative to the angular momentum vector) randomized during each thermal spike. We recompute the excitation and damping rates associated with rotational emission from the grain permanent dipole, grain-plasma interactions, infrared photon emission and collisions. The resulting spinning dust spectra generally show a shift towards higher emissivities and peak frequencies relative to previous calculations. [ABSTRACT FROM AUTHOR]

If the orientations of galaxies are correlated with large-scale structure, then anisotropic selection effects such as preferential selection of face-on disc galaxies can contaminate large-scale structure observables. Here we consider the effect on the galaxy bispectrum, which has attracted interest as a way to break the degeneracy between galaxy bias and the amplitude of matter fluctuations σ. We consider two models of intrinsic galaxy alignments: one where the probability distribution for the galaxy's orientation contains a term linear in the local tidal field, appropriate for elliptical galaxies; and one with a term quadratic in the local tidal field, which may be applicable to disc galaxies. We compute the correction to the redshift space bispectrum in the quasi-linear regime, and then focus on its effects on parameter constraints from the transverse bispectrum, i.e. using triangles in the plane of the sky. We show that in the linear alignment model, intrinsic alignments result in an error in the galaxy bias parameters, but do not affect the inferred value of σ. In contrast, the quadratic alignment model results in a systematic error in both the bias parameters and σ. However, the quadratic alignment effect has a unique configuration dependence that should enable it to be removed in upcoming surveys. [ABSTRACT FROM AUTHOR]

The Giant Metrewave Radio Telescope (GMRT) reionization effort aims to map out the large-scale structure of the Universe during the epoch of reionization (EoR). Removal of polarized Galactic emission is a difficult part of any 21 cm EoR programme, and we present new upper limits to diffuse polarized foregrounds at 150 MHz. We find no high-significance evidence of polarized emission in our observed field at mid-galactic latitude (J2000 08h26m+26). We find an upper limit on the two-dimensional angular power spectrum of diffuse polarized foregrounds of in frequency bins of width at . The three-dimensional power spectrum of polarized emission, which is most directly relevant to EoR observations, is at . This can be compared to the expected EoR signal in total intensity of . We find that polarized structure is substantially weaker than suggested by extrapolation from higher frequency observations, so the new low upper limits reported here reduce the anticipated impact of these foregrounds on EoR experiments. We discuss the Faraday beam and depth depolarization models and compare predictions of these models to our data. We report on a new technique for polarization calibration using pulsars, as well as a new technique to remove broad-band radio frequency interference. Our data indicate that, on the edges of the main beam at the GMRT, polarization squint creates ∼3 per cent leakage of unpolarized power into polarized maps at zero rotation measure. Ionospheric rotation was largely stable during these solar minimum nighttime observations. [ABSTRACT FROM AUTHOR]

Previous calculations of the pre-galactic chemistry have found that a small amount of , is produced catalytically through the and HeH+ mechanisms. We revisit this standard calculation taking into account the effects of the non-thermal radiation background produced by cosmic hydrogen recombination, which is particularly effective at destroying H− via photodetachment. We also take into consideration the non-equilibrium level populations of , which occur since transitions among the rotational–vibrational levels are slow compared to photodissociation. The new calculation predicts a final H2 abundance of for the standard cosmology. This production is due almost entirely to the H− mechanism, with ∼1 per cent coming from HeH+ and ∼0.004 per cent from . We evaluate the heating of the diffuse pre-galactic gas from the chemical reactions that produce H2 and from rotational transitions in H2, and find them to be negligible. [ABSTRACT FROM AUTHOR]

We present the results of attempts to detect the ellipticity of dark matter haloes using galaxy–galaxy weak lensing with Sloan Digital Sky Survey (SDSS) data. We use 2 020 256 galaxies brighter than with photometric redshifts (divided into colour and luminosity subsamples) as lenses and 31 697 869 source galaxies. We search for and identify several signal contaminants, which if not removed lead to a spurious detection. These include systematic shear that leads to a slight spurious alignment of lens and source ellipticities, intrinsic alignments (due to contamination of the source sample by physically associated lens–source pairs), and anisotropic magnification bias. We develop methods that allow us to remove these contaminants to the signal. We split the analysis into blue (spiral) and red (elliptical) galaxies. Assuming Gaussian errors as in previous work and a power-law profile, we find for red galaxies and for blue galaxies, using transverse separations of , averaged over luminosity. Inclusion of the more realistic non-Gaussian error distributions and of the Navarro–Frenk–White (NFW) density profile (which predicts much smaller ellipticity of the shear for scales above the scale radius) yields for ellipticals and for spirals. While there is no concrete detection of alignment in either case, there is a suggestion in the data of a positive alignment in the brightest lens sample of ellipticals. Our results appear to be mildly inconsistent with a previously reported detection by Hoekstra, Yee & Gladders, but more data and further tests are needed to clarify whether the discrepancy is real or a consequence of differences in the lens galaxy samples used and analysis methods. [ABSTRACT FROM AUTHOR]