Search NASA⌕ Search

SEARCH · Search NASA

Results for “Spatial variation”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

LOCAL TADPOLE GALAXIES: DYNAMICS AND METALLICITY

Tadpole galaxies, with a bright peripheral clump on a faint tail, are morphological types unusual in the nearby universe but very common early on. Low mass local tadpoles were identified and studied photometrically in a previous work, which we complete here analyzing their chemical and dynamical properties. We measure H{alpha} velocity curves of seven local tadpoles, representing 50% of the initial sample. Five of them show evidence for rotation ({approx}70%), and a sixth target hints at it. Often the center of rotation is spatially offset with respect to the tadpole head (three out of five cases). The size and velocity dispersion of the heads are typical of giant H II regions, and three of them yield dynamical masses in fair agreement with their stellar masses as inferred from photometry. In four cases the velocity dispersion at the head is reduced with respect to its immediate surroundings. The oxygen metallicity estimated from [N II] {lambda}6583/H{alpha} often shows significant spatial variations across the galaxies ({approx}0.5 dex), being smallest at the head and larger elsewhere. The resulting chemical abundance gradients are opposite to the ones observed in local spirals, but agrees with disk galaxies at high redshift. We interpret the metallicity variation as a sign of external gas accretion (cold-flows) onto the head of the tadpole. The galaxies are low-metallicity outliers of the mass-metallicity relationship. In particular, two of the tadpole heads are extremely metal poor, with a metallicity smaller than a tenth of the solar value. These two targets are also very young (ages smaller than 5 Myr). All these results combined are consistent with the local tadpole galaxies being disks in early stages of assembling, with their star formation sustained by accretion of external metal-poor gas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

MODEL-FREE MULTI-PROBE LENSING RECONSTRUCTION OF CLUSTER MASS PROFILES

Lens magnification by galaxy clusters induces characteristic spatial variations in the number counts of background sources, amplifying their observed fluxes and expanding the area of sky, the net effect of which, known as magnification bias, depends on the intrinsic faint-end slope of the source luminosity function. The bias is strongly negative for red galaxies, dominated by the geometric area distortion, whereas it is mildly positive for blue galaxies, enhancing the blue counts toward the cluster center. We generalize the Bayesian approach of Umetsu et al. for reconstructing projected cluster mass profiles, by incorporating multiple populations of background sources for magnification-bias measurements and combining them with complementary lens-distortion measurements, effectively breaking the mass-sheet degeneracy and improving the statistical precision of cluster mass measurements. The approach can be further extended to include strong-lensing projected mass estimates, thus allowing for non-parametric absolute mass determinations in both the weak and strong regimes. We apply this method to our recent CLASH lensing measurements of MACS J1206.2-0847, and demonstrate how combining multi-probe lensing constraints can improve the reconstruction of cluster mass profiles. This method will also be useful for a stacked lensing analysis, combining all lensing-related effects in the cluster regime, for a definitive determination of the averaged mass profile.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE FORMATION OF IRIS DIAGNOSTICS. II. THE FORMATION OF THE Mg II h and k LINES IN THE SOLAR ATMOSPHERE

NASA's Interface Region Imaging Spectrograph (IRIS) small explorer mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h and k lines as well as a slit-jaw imager centered at Mg II k. Understanding the observations requires forward modeling of Mg II h and k line formation from three-dimensional (3D) radiation-magnetohydrodynamic (RMHD) models. This paper is the second in a series where we undertake this modeling. We compute the vertically emergent h and k intensity from a snapshot of a dynamic 3D RMHD model of the solar atmosphere, and investigate which diagnostic information about the atmosphere is contained in the synthetic line profiles. We find that the Doppler shift of the central line depression correlates strongly with the vertical velocity at optical depth unity, which is typically located less than 200 km below the transition region (TR). By combining the Doppler shifts of the h and k lines we can retrieve the sign of the velocity gradient just below the TR. The intensity in the central line depression is anti-correlated with the formation height, especially in subfields of a few square Mm. This intensity could thus be used to measure the spatial variation of the height of the TR. The intensity in the line-core emission peaks correlates with the temperature at its formation height, especially for strong emission peaks. The peaks can thus be exploited as a temperature diagnostic. The wavelength difference between the blue and red peaks provides a diagnostic of the velocity gradients in the upper chromosphere. The intensity ratio of the blue and red peaks correlates strongly with the average velocity in the upper chromosphere. We conclude that the Mg II h and k lines are excellent probes of the very upper chromosphere just below the TR, a height regime that is impossible to probe with other spectral lines. They also provide decent temperature and velocity diagnostics of the middle chromosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE STRUCTURE OF THE EVOLVED CIRCUMBINARY DISK AROUND V4046 Sgr

We present sensitive, sub-arcsecond resolution Submillimeter Array observations of the protoplanetary disk around the nearby, pre-main sequence spectroscopic binary V4046 Sgr. We report for the first time a large inner hole (r = 29 AU) spatially resolved in the 1.3 mm continuum emission and study the structure of this disk using radiative transfer calculations to model the spectral energy distribution, continuum visibilities, and spectral line emission of CO and its main isotopologues. Our modeling scheme demonstrates that the majority of the dust mass is distributed in a narrow ring (centered at 37 AU with a FWHM of 16 AU) that is ∼5× more compact than the gas disk. This structure implies that the dust-to-gas mass ratio has a strong spatial variation, ranging from a value much larger than typical of the interstellar medium (ISM) at the ring to much smaller than that of the ISM at larger disk radii. We suggest that these basic structural features are potentially observational signatures of the accumulation of solids at a local gas pressure maximum. These models also require a substantial population of ∼μm sized grains inside the central disk cavity. We suggest that this structure is likely the result of dynamical interactions with a low-mass companion, although photoevaporation may also play a secondary role.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

An alma survey of submillimeter galaxies in the extended Chandra deep field-south: The agn fraction and X-ray properties of submillimeter galaxies

The large gas and dust reservoirs of submillimeter galaxies (SMGs) could potentially provide ample fuel to trigger an active galactic nucleus (AGN), but previous studies of the AGN fraction in SMGs have been controversial largely due to the inhomogeneity and limited angular resolution of the available submillimeter surveys. Here we set improved constraints on the AGN fraction and X-ray properties of the SMGs with Atacama Large Millimeter/submillimeter Array (ALMA) and Chandra observations in the Extended Chandra Deep Field-South (E-CDF-S). This study is the first among similar works to have unambiguously identified the X-ray counterparts of SMGs; this is accomplished using the fully submillimeter-identified, statistically reliable SMG catalog with 99 SMGs from the ALMA LABOCA E-CDF-S Submillimeter Survey. We found 10 X-ray sources associated with SMGs (median redshift z = 2.3), of which eight were identified as AGNs using several techniques that enable cross-checking. The other two X-ray detected SMGs have levels of X-ray emission that can be plausibly explained by their star formation activity. Six of the eight SMG-AGNs are moderately/highly absorbed, with N {sub H} > 10{sup 23} cm{sup –2}. An analysis of the AGN fraction, taking into account the spatial variation of X-ray sensitivity, yields an AGN fraction of 17{sub −6}{sup +16}% for AGNs with rest-frame 0.5-8 keV absorption-corrected luminosity ≥7.8 × 10{sup 42} erg s{sup –1}; we provide estimated AGN fractions as a function of X-ray flux and luminosity. ALMA's high angular resolution also enables direct X-ray stacking at the precise positions of SMGs for the first time, and we found four potential SMG-AGNs in our stacking sample.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Are cosmic rays modulated beyond the heliopause?

We discuss the possible spatial variation of Galactic and anomalous cosmic rays (GCRs and ACRs) at and beyond the heliopause (HP). Remaining within the framework of the Parker transport equation and assuming incompressible plasma in the heliosheath, we consider highly idealized simple-flow models and compare our GCR results with recent publications of Scherer et al. and Strauss et al. First, we discuss an order-of-magnitude estimate and a simple spherical model to demonstrate that the modulation of GCRs beyond the HP must be quite small if the diffusion coefficient beyond the HP is greater than ≈10{sup 26} cm{sup 2} s{sup –1}, a value that is two orders of magnitude smaller than the value of 10{sup 28} cm{sup 2} s{sup –1} determined from observations of GCR composition. Second, we construct a non-spherical model, which allows lateral deflection of the flow and uses different diffusion coefficients parallel and perpendicular to the magnetic field. We find that modulation of GCRs beyond the HP remains small even if the perpendicular diffusion coefficient beyond the HP is quite small (≈10{sup 22} cm{sup 2} s{sup –1}) as long as the parallel diffusion is sufficiently fast. We also consider the case when the parallel diffusion beyond the HP is fast, but the perpendicular diffusion is as small as ≈10{sup 20} cm{sup 2} s{sup –1}; this results in a sharp, almost step-like increase of GCR flux (and decrease of ACRs) at the HP. Possible implications are briefly discussed. We further suggest the possibility that the observed sharp gradient of GCRs at the HP might push the HP closer to the Sun than previously thought.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

An interpretation of flare-induced and decayless coronal-loop oscillations as interference patterns

We present an alternative model of coronal-loop oscillations, which considers that the waves are trapped in a two-dimensional waveguide formed by the entire arcade of field lines. This differs from the standard one-dimensional model which treats the waves as the resonant oscillations of just the visible bundle of field lines. Within the framework of our two-dimensional model, the two types of oscillations that have been observationally identified, flare-induced waves and 'decayless' oscillations, can both be attributed to MHD fast waves. The two components of the signal differ only because of the duration and spatial extent of the source that creates them. The flare-induced waves are generated by strong localized sources of short duration, while the decayless background can be excited by a continuous, stochastic source. Further, the oscillatory signal arising from a localized, short-duration source can be interpreted as a pattern of interference fringes produced by waves that have traveled diverse routes of various pathlengths through the waveguide. The resulting amplitude of the fringes slowly decays in time with an inverse square root dependence. The details of the interference pattern depend on the shape of the arcade and the spatial variation of the Alfvén speed. The rapid decay of this wave component, which has previously been attributed to physical damping mechanisms that remove energy from resonant oscillations, occurs as a natural consequence of the interference process without the need for local dissipation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The atmospheric circulation and observable properties of non-synchronously rotating hot Jupiters

We study the feasibility of observationally constraining the rotation rate of hot Jupiters, planets that are typically assumed to have been tidally locked into synchronous rotation. We use a three-dimensional General Circulation Model to solve for the atmospheric structure of two hot Jupiters (HD 189733b and HD 209458b), assuming rotation periods that are 0.5, 1, or 2 times their orbital periods (2.2 and 3.3 days, respectively), including the effect of variable stellar heating. We compare two observable properties: (1) the spatial variation of flux emitted by the planet, measurable in orbital phase curves, and (2) the net Doppler shift in transmission spectra of the atmosphere, which is tantalizingly close to being measurable in high-resolution transit spectra. Although we find little difference between the observable properties of the synchronous and non-synchronous models of HD 189733b, we see significant differences when we compare the models of HD 209458b. In particular, the slowly rotating model of HD 209458b has an atmospheric circulation pattern characterized by westward flow and an orbital phase curve that peaks after secondary eclipse (in contrast to all of our other models), while the quickly rotating model has a net Doppler shift that is more strongly blueshifted than the other models. Our results demonstrate that the combined use of these two techniques may be a fruitful way to constrain the rotation rate of some planets and motivate future work on this topic.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The mid-infrared appearance of the galactic mini-starburst W49A

The massive star-forming region W49A represents one of the largest complexes of massive star formation present in the Milky Way and contains at least 50 young massive stars still enshrouded in their natal molecular cloud. We employ Spitzer/Infrared Spectrometer spectral mapping observations of the northern part of W49A to investigate the mid-infrared (MIR) spatial appearance of the polycyclic aromatic hydrocarbon (PAH) bands, PAH plateau features, atomic lines, and continuum emission. We examine the spatial variations of the MIR emission components in slices through two of the ultra-compact-H II (UC-H II) regions. We find that the PAH bands reproduce known trends, with the caveat that the 6.2 μm PAH band seems to decouple from the other ionized PAH bands in some of the UC-H II regions—an effect previously observed only in one other object: the giant star forming region N66 in the Large Magellanic Cloud. Furthermore, we compare the nature of the emission surrounding W49A to that of 'diffuse' sightlines. It is found that the surrounding emission can be explained by line of sight emission and does not represent true 'diffuse' material. Additionally, we examine the MIR appearance of star formation on various scales from UC-H II regions to starburst galaxies, including a discussion of the fraction of PAH emission in the 8 μm IRAC filter. We find that the MIR appearance of W49A is that of a starburst on large scales, yet its individual components are consistent with other galactic H II regions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

ALMA OBSERVATIONS OF THE DEBRIS DISK AROUND THE YOUNG SOLAR ANALOG HD 107146

We present the Atacama Large Millimeter/submillimeter Array (ALMA) continuum observations at a wavelength of 1.25 mm of the debris disk surrounding the ∼100 Myr old solar analog HD 107146. The continuum emission extends from about 30 to 150 AU from the central star with a decrease in the surface brightness at intermediate radii. We analyze the ALMA interferometric visibilities using debris disk models with radial profiles for the dust surface density parameterized as (1) a single power law, (2) a single power law with a gap, and (3) a double power law. We find that models with a gap of radial width ∼8 AU at a distance of ∼80 AU from the central star, as well as double power-law models with a dip in the dust surface density at ∼70 AU provide significantly better fits to the ALMA data than single power-law models. We discuss possible scenarios for the origin of the HD 107146 debris disk using models of planetesimal belts in which the formation of Pluto-sized objects trigger disruptive collisions of large bodies, as well as models that consider the interaction of a planetary system with a planetesimal belt and spatial variation of the dust opacity across the disk. If future observations with higher angular resolution and sensitivity confirm the fully depleted gap structure discussed here, a planet with a mass of approximately a few Earth masses in a nearly circular orbit at ∼80 AU from the central star would be a possible explanation for the presence of the gap.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The role of bulge formation in the homogenization of stellar populations at Z ∼ 2 as revealed by internal color dispersion in candels

We use data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey to study how the spatial variation in the stellar populations of galaxies relates to the formation of galaxies at 1.5 2) show reduced ICD values, implying a greater homogeneity of their stellar populations. This indicates that if a galaxy is to have a quiescent bulge along with a star-forming disk, typical of Hubble sequence galaxies, this is most common for stellar masses 10 < log (M/M{sub ⊙}) < 11 and when the bulge component remains relatively small (n<2).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

ALMA multi-line observations of the IR-bright merger VV 114

We present Atacama Large Millimeter/submillimeter Array cycle 0 observations of the molecular gas and dust in the IR-bright mid-stage merger VV 114 obtained at 160–800 pc resolution. The main aim of this study is to investigate the distribution and kinematics of the cold/warm gas and to quantify the spatial variation of the excitation conditions across the two merging disks. The data contain 10 molecular lines, including the first detection of extranuclear CH{sub 3}OH emission in interacting galaxies, as well as continuum emission. We map the {sup 12}CO(3–2)/{sup 12}CO(1–0) and the {sup 12}CO(1–0)/{sup 13}CO(1–0) line ratio at 800 pc resolution (in the units of K km s{sup −1}), and find that these ratios vary from 0.2–0.8 and 5–50, respectively. Conversely, the 200 pc resolution HCN(4–3)/HCO{sup +}(4–3) line ratio shows low values (<0.5) at a filament across the disks except for the unresolved eastern nucleus which is three times higher (1.34 ± 0.09). We conclude from our observations and a radiative transfer analysis that the molecular gas in the VV 114 system consists of five components with different physical and chemical conditions, i.e., (1) dust-enshrouded nuclear starbursts and/or active galactic nuclei, (2) widespread star-forming dense gas, (3) merger-induced shocked gas, (4) quiescent tenuous gas arms without star formation, and (5) H{sub 2} gas mass of (3.8 ± 0.7) × 10{sup 7} M{sub ⊙} (assuming a conversion factor of α{sub CO} = 0.8 M{sub ⊙} (K km s{sup −1} pc{sup 2}){sup −1}) at the tip of the southern tidal arm, as a potential site of tidal dwarf galaxy formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

MASS SUBSTRUCTURE IN ABELL 3128

We perform a detailed two-dimensional weak gravitational lensing analysis of the nearby (z = 0.058) galaxy cluster Abell 3128 using deep ugrz imaging from the Dark Energy Camera (DECam). We have designed a pipeline to remove instrumental artifacts from DECam images and stack multiple dithered observations without inducing a spurious ellipticity signal. We develop a new technique to characterize the spatial variation of the point-spread function that enables us to circularize the field to better than 0.5% and thereby extract the intrinsic galaxy ellipticities. By fitting photometric redshifts to sources in the observation, we are able to select a sample of background galaxies for weak-lensing analysis free from low-redshift contaminants. Photometric redshifts are also used to select a high-redshift galaxy subsample with which we successfully isolate the signal from an interloping z = 0.44 cluster. We estimate the total mass of Abell 3128 by fitting the tangential ellipticity of background galaxies with the weak-lensing shear profile of a Navarro–Frenk–White (NFW) halo and also perform NFW fits to substructures detected in the 2D mass maps of the cluster. This study yields one of the highest resolution mass maps of a low-z cluster to date and is the first step in a larger effort to characterize the redshift evolution of mass substructures in clusters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The relationship between the dust and gas-phase co across the California molecular cloud

We present results of an extinction-CO line survey of the southeastern part of the California molecular cloud (CMC). Deep, wide-field, near-infrared images were used to construct a sensitive, relatively high resolution (∼0.5 arcmin) (NICEST) extinction map of the region. The same region was also surveyed in the {sup 12}CO(2–1), {sup 13}CO(2–1), and C{sup 18}O(2–1) emission lines at the same angular resolution. These data were used to investigate the relation between the molecular gas, traced by CO emission lines, and the dust column density, traced by extinction, on spatial scales of 0.04 pc across the cloud. We found strong spatial variations in the abundances of {sup 13}CO and C{sup 18}O that were correlated with variations in gas temperature, consistent with temperature-dependent CO depletion/desorption on dust grains. The {sup 13}CO-to-C{sup 18}O abundance ratio was found to increase with decreasing extinction, suggesting selective photodissociation of C{sup 18}O by the ambient UV radiation field. The effect is particularly pronounced in the vicinity of an embedded cluster where the UV radiation appears to have penetrated deeply (i.e., A{sub V} ≲ 15 mag) into the cloud. We derived the cloud-averaged X-factor to be 〈X{sub CO} 〉 = 2.53 × 10{sup 20} cm{sup −2}(K km s{sup −1}){sup −1}, a value somewhat higher than the Milky Way average. On sub-parsec scales we find there is no single empirical value of the {sup 12}CO X-factor that can characterize the molecular gas in cold (T{sub k} ≲ 15 K) cloud regions, with X{sub CO} ∝ A{sub V}{sup 0.74} for A{sub V} ≳ 3 mag. However, in regions containing relatively hot (T{sub ex} ≳ 25 K) molecular gas we find a clear correlation between W({sup 12}CO) and A{sub V} over a large (3 ≲ A{sub V} ≲ 25 mag) range of extinction. This results in a constant X{sub CO} = 1.5 × 10{sup 20} cm{sup −2} (K km s{sup −1}){sup −1} for the hot gas, a lower value than either the average for the CMC or the Milky Way. Overall we find an (inverse) correlation between X{sub CO} and T{sub ex} in the cloud with X{sub CO} ∝ T{sub ex} {sup −0.7}. This correlation suggests that the global X-factor of a giant molecular cloud may depend on the relative amounts of hot gas contained within the cloud.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE MEGASECOND CHANDRA X-RAY VISIONARY PROJECT OBSERVATION OF NGC 3115. III. LUMINOSITY FUNCTIONS OF LMXBS AND DEPENDENCE ON STELLAR ENVIRONMENTS

We studied the X-ray luminosity function (XLF) of low-mass X-ray binaries (LMXBs) in the nearby lenticular galaxy NGC 3115, using the Megasecond Chandra X-ray Visionary Project Observation. With a total exposure time of ∼1.1 Ms, we constructed the XLF down to a limiting luminosity of ∼10{sup 36} erg s{sup −1}, which is much deeper than that typically reached for other early-type galaxies. We found significant flattening of the overall LMXB XLF from dN/dL ∝ L{sup −2.2±0.4} above 5.5 × 10{sup 37} erg s{sup −1} to dN/dL ∝ L{sup −1.0±0.1} below it, although we could not rule out a fit with a higher break at ∼1.6 × 10{sup 38} erg s{sup −1}. We also found evidence that the XLF of LMXBs in globular clusters (GCs) is overall flatter than that of field LMXBs. Thus, our results for this galaxy do not support the idea that all LMXBs are formed in GCs. The XLF of field LMXBs seems to show spatial variation, with the XLF in the inner region of the galaxy being flatter than that in the outer region, probably due to contamination of LMXBs from undetected and/or disrupted GCs in the inner region. The XLF in the outer region is probably the XLF of primordial field LMXBs, exhibiting dN/dL ∝ L{sup −1.2±0.1} up to a break close to the Eddington limit of neutron star LMXBs (∼1.7 × 10{sup 38} erg s{sup −1}). The break of the GC LMXB XLF is lower, at ∼1.1 × 10{sup 37} erg s{sup −1}. We also confirm previous findings that the metal-rich/red GCs are more likely to host LMXBs than the metal-poor/blue GCs, which is more significant for more luminous LMXBs, and that more massive GCs are more likely to host LMXBs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

APPARENT CROSS-FIELD SUPERSLOW PROPAGATION OF MAGNETOHYDRODYNAMIC WAVES IN SOLAR PLASMAS

In this paper we show that the phase-mixing of continuum Alfvén waves and/or continuum slow waves in the magnetic structures of the solar atmosphere as, e.g., coronal arcades, can create the illusion of wave propagation across the magnetic field. This phenomenon could be erroneously interpreted as fast magnetosonic waves. The cross-field propagation due to the phase-mixing of continuum waves is apparent because there is no real propagation of energy across the magnetic surfaces. We investigate the continuous Alfvén and slow spectra in two-dimensional (2D) Cartesian equilibrium models with a purely poloidal magnetic field. We show that apparent superslow propagation across the magnetic surfaces in solar coronal structures is a consequence of the existence of continuum Alfvén waves and continuum slow waves that naturally live on those structures and phase-mix as time evolves. The apparent cross-field phase velocity is related to the spatial variation of the local Alfvén/slow frequency across the magnetic surfaces and is slower than the Alfvén/sound velocities for typical coronal conditions. Understanding the nature of the apparent cross-field propagation is important for the correct analysis of numerical simulations and the correct interpretation of observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

THE CARNEGIE-IRVINE GALAXY SURVEY. I. OVERVIEW AND ATLAS OF OPTICAL IMAGES

The Carnegie-Irvine Galaxy Survey (CGS) is a long-term program to investigate the photometric and spectroscopic properties of a statistically complete sample of 605 bright (B{sub T} < 12.9 mag), southern ({delta} < 0 Degree-Sign ) galaxies using the facilities at Las Campanas Observatory. This paper, the first in a series, outlines the scientific motivation of CGS, defines the sample, and describes the technical aspects of the optical broadband (BVRI) imaging component of the survey, including details of the observing program, data reduction procedures, and calibration strategy. The overall quality of the images is quite high, in terms of resolution (median seeing {approx}1''), field of view (8.'9 Multiplication-Sign 8.'9), and depth (median limiting surface brightness {approx}27.5, 26.9, 26.4, and 25.3 mag arcsec{sup -2} in the B, V, R, and I bands, respectively). We prepare a digital image atlas showing several different renditions of the data, including three-color composites, star-cleaned images, stacked images to enhance faint features, structure maps to highlight small-scale features, and color index maps suitable for studying the spatial variation of stellar content and dust. In anticipation of upcoming science analyses, we tabulate an extensive set of global properties for the galaxy sample. These include optical isophotal and photometric parameters derived from CGS itself, as well as published information on multiwavelength (ultraviolet, U-band, near-infrared, far-infrared) photometry, internal kinematics (central stellar velocity dispersions, disk rotational velocities), environment (distance to nearest neighbor, tidal parameter, group, or cluster membership), and H I content. The digital images and science-level data products will be made publicly accessible to the community.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

IMAGE ANALYSIS FOR COSMOLOGY: RESULTS FROM THE GREAT10 STAR CHALLENGE

We present the results from the first public blind point-spread function (PSF) reconstruction challenge, the GRavitational lEnsing Accuracy Testing 2010 (GREAT10) Star Challenge. Reconstruction of a spatially varying PSF, sparsely sampled by stars, at non-star positions is a critical part in the image analysis for weak lensing where inaccuracies in the modeled ellipticity e and size R {sup 2} can impact the ability to measure the shapes of galaxies. This is of importance because weak lensing is a particularly sensitive probe of dark energy and can be used to map the mass distribution of large scale structure. Participants in the challenge were presented with 27,500 stars over 1300 images subdivided into 26 sets, where in each set a category change was made in the type or spatial variation of the PSF. Thirty submissions were made by nine teams. The best methods reconstructed the PSF with an accuracy of {sigma}(e) Almost-Equal-To 2.5 Multiplication-Sign 10{sup -4} and {sigma}(R {sup 2})/R {sup 2} Almost-Equal-To 7.4 Multiplication-Sign 10{sup -4}. For a fixed pixel scale, narrower PSFs were found to be more difficult to model than larger PSFs, and the PSF reconstruction was severely degraded with the inclusion of an atmospheric turbulence model (although this result is likely to be a strong function of the amplitude of the turbulence power spectrum).

79 ASTRONOMY AND ASTROPHYSICS↗