We present a three-dimensional cosmic shear analysis of the Hubble Space Telescope COSMOS survey, the largest ever optical imaging program performed In space. We have measured the shapes of galaxies ...for the telltale distortions caused by weak gravitational tensing and traced the growth of that signal as a function of redshift. Using both 2D and 3D analyses, we measure cosmological parameters Omega sub(m), the density of matter in the universe, and sigma sub(8), the normalization of the matter power spectrum. The introduction of redshift information tightens the constraints by a factor of 3 and also reduces the relative sampling (or "cosmic") variance compared to recent surveys that may be larger but are only two-dimensional. From the 3D analysis, we find that sigma sub(8)( Omega sub(m)/0.3) super(0.44) = 0.866 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(0) sub(0) super(8) sub(6) super(5) sub(8) 68% confidence limits, Including both statistical and potential systematic sources of error in the total budget. Indeed, the absolute calibration of shear measurement methods is now the dominant source of uncertainty. Assuming instead a baseline cosmology to fix the geometry of the universe, we have measured the growth of structure on both linear and nonlinear physical scales. Our results thus demonstrate a proof of concept for tomographic analysis techniques that have been proposed for future weak-lensing surveys by a dedicated wide-field telescope in space.
We present the results of the Gravitational LEnsing Accuracy Testing 2008 (GREAT08) Challenge, a blind analysis challenge to infer weak gravitational lensing shear distortions from images. The ...primary goal was to stimulate new ideas by presenting the problem to researchers outside the shear measurement community. Six GREAT08 Team methods were presented at the launch of the Challenge and five additional groups submitted results during the 6-month competition. Participants analyzed 30 million simulated galaxies with a range in signal-to-noise ratio, point spread function ellipticity, galaxy size and galaxy type. The large quantity of simulations allowed shear measurement methods to be assessed at a level of accuracy suitable for currently planned future cosmic shear observations for the first time. Different methods perform well in different parts of simulation parameter space and come close to the target level of accuracy in several of these. A number of fresh ideas have emerged as a result of the Challenge including a re-examination of the process of combining information from different galaxies, which reduces the dependence on realistic galaxy modelling. The image simulations will become increasingly sophisticated in future GREAT Challenges, meanwhile the GREAT08 simulations remain as a benchmark for additional developments in shear measurement algorithms.
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BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
We used a grid‐mapping technique to analyze the distribution of 13 water‐ and ice‐related landforms in Acidalia Planitia as part of a joint effort to study the three main basins in the northern ...lowlands of Mars, that is, Acidalia, Utopia, and Arcadia Planitiae. The landforms were mapped at full Context Camera resolution along a 300‐km‐wide strip from 20°N to 84°N. We identified four landform assemblages: (1) Geologically recent polar cap (massive ice), which superposes the latitude‐dependent mantle (LDM) (LA1); (2) ice‐related landforms, such as LDM, textured terrain, small‐scale polygons, scalloped terrain, large‐scale viscous flow features, and gullies, which have an overlapping distribution (LA2); (3) surface features possibly related to water and subsurface sediment mobilization (LA3; kilometer‐scale polygons, large pitted mounds, small pitted mounds, thumbprint terrain); and (4) irregularly shaped pits with raised rims on equator‐facing slopes. Pits are likely the result of an energetic release of volatiles (H2O, CO2, and CH4), rather than impact‐, volcanism‐, or wind‐related processes. LDM occurs ubiquitously from 44°N to 78°N in Acidalia Planitia. Various observations suggest an origin of air fall deposition of LDM, which contains less ice in the uppermost tens of meters in Acidalia Planitia than in Arcadia and Utopia Planitiae. However, LDM may be thicker and more extended in the past in Acidalia Planitia. The transition between LDM‐free terrain and LDM is situated further north than in Utopia and Arcadia Planitiae, suggesting different past and/or present climatic conditions among the main basins in the northern lowlands.
Plain Language Summary
We studied water and ice‐related landforms in the Acidalia Planitia, Mars. We used a new approach, a grid system of 20 × 20‐km cells, along a 300‐km‐wide strip (east‐west) from latitude 20°N to 84°N (south‐north). This work is a joint effort to study three major basins in the northern plains: Acidalia, Utopia, and Arcadia Planitiae. We conducted a regional mapping of specific landforms at 6 m/pixel resolution data and compared the results to different data products, such as geological maps, topography, radar, and climatic models. We proved that latitude‐dependent mantle occurs from 44°N to 78°N in Acidalia Planitia and has an air fall origin related to past climatic cycles. These deposits are composed of mixture of fine‐grained ice and dust. The distribution of this landform extends further south in Utopia and Arcadia Planitae suggesting different past/present climatic conditions in the northern lowlands.
Key Points
A grid‐mapping approach is demonstrated to be an effective technique to map small‐scale landforms in Acidalia Planitia
LDM begins to occur north of 44 degree N in Acidalia Planitia, a transition that is at a higher latitude than in Utopia and Arcadia Planitiae
Irregular‐shaped pits on equator‐facing scarps suggest an energetic release of volatiles (H2O, CO2, CH4)
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We examine the effects of charge transfer inefficiency (CTI) during CCD readout on the demanding galaxy shape measurements required by studies of weak gravitational lensing. We simulate a CCD readout ...with CTI such as that caused by charged particle radiation damage in space-based detectors. We verify our simulations on real data from fully depleted p-channel CCDs that have been deliberately irradiated in a laboratory. We show that only charge traps with time constants of the same order as the time between row transfers during readout affect galaxy shape measurements. We simulate deep astronomical images and the process of CCD readout, characterizing the effects of CTI on various galaxy populations. Our code and methods are general and can be applied to any CCDs, once the density and characteristic release times of their charge trap species are known. We baseline our study around p-channel CCDs that have been shown to have charge transfer efficiency up to an order of magnitude better than several models of n-channel CCDs designed for space applications. We predict that for galaxies furthest from the readout registers, bias in the measurement of galaxy shapes,Δe
Δ
e
, will increase at a rate of(2.65 ± 0.02) × 10-4 yr-1
(
2.65
±
0.02
)
×
10
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4
y
r
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1
at L2 for accumulated radiation exposure averaged over the solar cycle. If uncorrected, this will consume the entire shape measurement error budget of a dark energy mission surveying the entire extragalactic sky within about 4 yr of accumulated radiation damage. However, software mitigation techniques demonstrated elsewhere can reduce this by a factor of∼10
∼
10
, bringing the effect well below mission requirements. This conclusion is valid only for the p-channel CCDs we have modeled; CCDs with higher CTI will fare worse and may not meet the requirements of future dark energy missions. We also discuss additional ways in which hardware could be designed to further minimize the impact of CTI.
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BFBNIB, NMLJ, NUK, PNG, UL, UM, UPUK
Large‐scale changes in forest structure and ecological function throughout western North America have led to increased frequency, size, and severity of wildfires. The US Forest Service is ...implementing state‐wide forest restoration initiatives to reduce wildfire hazards and improve forest health. We provide a synthesis of pre‐ and post‐treatment forest vegetation and ecosystem moisture trends between 1990 and 2017 in Arizona, the first US state where the initiative has implemented a variety of thinning and burning methods in over 1,200 polygon areas across 3.5 million ha. Using 4,426 Landsat satellite images on Google Earth Engine, we calculated normalized difference moisture index (NDMI), normalized difference water index (NDWI), and normalized difference vegetation index (NDVI) to create dense time‐series datasets. The indices and 1990‐2017 annual total precipitation dataset were then examined using a Mann–Kendall tau test to identify statistically significant upward and downward trends for each pixel. Our results indicate that much of the study region were experiencing drought conditions prior to restoration treatments and NDVI values were significantly decreasing, especially during the dry spring season. However, both NDMI and NDWI trends indicate that the forest restoration treatments have contributed to increased total ecosystem moisture, while precipitation in the post‐treatment period exhibit stable trends. Forest restoration treatments appear to have improved the overall forest health and resiliency to drought, especially during the dry spring season, when forests are most vulnerable to water stress and wildfire risks. Our results of the spatial patterns and long‐term trends in these variables can inform the currently ongoing and future restoration treatments to better target the treatment strategy across the southwestern USA. Google Earth Engine enabled our synthesis of these long‐term trends over the large region and will enhance our continued monitoring in the coming decade.
We provide a synthesis of the regional‐scale forest restoration treatments implemented across 3.5 million ha in Arizona, USA. Our analysis of over 4,400 Landsat images on Google Earth Engine indicates that forest thinning and burning treatments have significantly improved forest health and resiliency to drought.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Dysregulation of the complement system has been described in patients with heart failure (HF). However, data on the alternative pathway are scarce and it is unknown if levels of factor B (FB) and the ...C3 convertase C3bBbP are elevated in these patients. We hypothesized that plasma levels of FB and C3bBbP would be associated with disease severity and survival in patients with HF.
We analyzed plasma levels of FB, C3bBbP, and terminal C5b-9 complement complex (TCC) in 343 HF patients and 27 healthy controls.
Compared with controls, patients with HF had elevated levels of circulating FB (1.6-fold, p < 0.001) and C3bBbP (1.3-fold, p < 0.001). In contrast, TCC, reflecting the terminal pathway, was not significantly increased (p = 0.15 vs controls). FB was associated with NT-proBNP, troponin, eGFR, and i.e., C-reactive protein. FB, C3bBbP and TCC were not associated with mortality in HF during a mean follow up of 4.3 years.
Our findings suggest that in patients with HF, the alternative pathway is activated. However, this is not accompanied by activation of the terminal pathway.
Abstract SuperBIT was a 0.5 m near-UV to near-infrared wide-field telescope that launched on a NASA superpressure balloon into the stratosphere from New Zealand for a 45-night flight. SuperBIT ...acquired multiband images of galaxy clusters to study the properties of dark matter using weak gravitational lensing. We provide an overview of the instrument and its various subsystems. We then present the instrument performance from the flight, including the telescope and image stabilization system, the optical system, the power system, and the thermal system. SuperBIT successfully met the instrument’s technical requirements, achieving a telescope pointing stability of 0.″34 ± 0.″10, a focal plane image stability of 0.″055 ± 0.″027, and a point-spread function FWHM of ∼0.″35 over 5-minute exposures throughout the 45-night flight. The telescope achieved a near-diffraction-limited point-spread function in all three science bands ( u , b , and g ). SuperBIT served as a pathfinder to the GigaBIT observatory, which will be a 1.34 m near-UV to near-infrared balloon-borne telescope.
We examine the spatial and temporal stability of the Hubble Space Telescope's Advanced Camera for Surveys (ACS) Wide Field Camera (WFC) point-spread function (PSF) using the 2 deg super(2) COSMOS ...survey. This is important for studies of weak gravitational lensing, where the ability to deconvolve the PSF from galaxy shapes is of paramount importance. We show that stochastic aliasing of the PSF necessarily occurs during "drizzling." This aliasing is maximal if the output-pixel scale is equal to the input-pixel scale. This source of PSF variation can be significantly reduced by choosing a Gaussian drizzle kernel with a size of 0.8 input pixels and by reducing the output-pixel scale. We show that the PSF is temporally unstable, resulting in an overall slow periodic focus change in the COSMOS images. Using a modified version of the Tiny Tim PSF modeling software, we create grids of undistorted stars over a range of telescope focus values. We then use the approximately 10 well-measured stars in each COSMOS field to pick the best-fit focus value for each field. The Tiny Tim model stars can then be used to perform PSF corrections for weak lensing. We derive a parametric correction for the effect of charge transfer efficiency (CTE) degradation on the shapes of objects in the COSMOS field as a function of observation date, position within the ACS WFC field, and object flux. Finally, we discuss future plans to improve the CTE correction.
We present the results of an ongoing weak-lensing survey conducted with the Subaru Telescope whose initial goal is to locate and study the distribution of shear-selected structures, or halos. Using a ...Suprime-Cam imaging survey spanning 21.82 deg super(2), we present a catalog of 100 candidate halos located from lensing-convergence maps. Our sample is reliably drawn from that subset of our survey area (totaling 16.72 deg super(2)) uncontaminated by bright stars and edge effects and is limited at a convergence signal-to-noise ratio of 3.69. To validate the sample, detailed spectroscopic measures have been made for 26 candidates using the Subaru multiobject spectrograph, FOCAS. All are confirmed as clusters of galaxies, but two arise as the superposition of multiple clusters viewed along the line of sight. Including data available in the literature and an ongoing Keck spectroscopic campaign, a total of 41 halos now have reliable redshifts. For one of our survey fields, the XMM-LSS field, we compare our lensing-selected halo catalog with its X-ray equivalent. Of 15 halos detected in the XMM-LSS field, 10 match published X-ray-selected clusters, and a further two are newly detected and spectroscoplcally confirmed in this work. Although three halos have not yet been confirmed, the high success rate within the XMM-LSS field (12/15) confirms that weak lensing provides a reliable method for constructing cluster catalogs, irrespective of the nature of the constituent galaxies or the intracluster medium.
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