Results 1 - 10 of 3567
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[en] We introduce a novel method to measure the masses of galaxy clusters at high redshift selected from optical and IR Spitzer data via the red-sequence technique. Lyman-break galaxies are used as a well-understood, high-redshift background sample allowing mass measurements of lenses at unprecedented high redshifts using weak lensing magnification. By stacking a significant number of clusters at different redshifts with average masses of ∼(1-3) x 1014 Msun, as estimated from their richness, we can calibrate the normalization of the mass-richness relation. With the current data set (area: 6 deg2) we detect a magnification signal at the >3σ level. There is good agreement between the masses estimated from the richness of the clusters and the average masses estimated from magnification, albeit with large uncertainties. We perform tests that suggest the absence of strong systematic effects and support the robustness of the measurement. This method-when applied to larger data sets in the future-will yield an accurate calibration of the mass-observable relations at z ∼> 1 which will represent an invaluable input for cosmological studies using the galaxy cluster mass function and astrophysical studies of cluster formation. Furthermore, this method will probably be the least expensive way to measure masses of large numbers of z > 1 clusters detected in future IR-imaging surveys.
[en] The Spitzer Extended Deep Survey (SEDS) is a very deep infrared survey within five well-known extragalactic science fields: the UKIDSS Ultra-Deep Survey, the Extended Chandra Deep Field South, COSMOS, the Hubble Deep Field North, and the Extended Groth Strip. SEDS covers a total area of 1.46 deg2 to a depth of 26 AB mag (3σ) in both of the warm Infrared Array Camera (IRAC) bands at 3.6 and 4.5 μm. Because of its uniform depth of coverage in so many widely-separated fields, SEDS is subject to roughly 25% smaller errors due to cosmic variance than a single-field survey of the same size. SEDS was designed to detect and characterize galaxies from intermediate to high redshifts (z = 2-7) with a built-in means of assessing the impact of cosmic variance on the individual fields. Because the full SEDS depth was accumulated in at least three separate visits to each field, typically with six-month intervals between visits, SEDS also furnishes an opportunity to assess the infrared variability of faint objects. This paper describes the SEDS survey design, processing, and publicly-available data products. Deep IRAC counts for the more than 300,000 galaxies detected by SEDS are consistent with models based on known galaxy populations. Discrete IRAC sources contribute 5.6 ± 1.0 and 4.4 ± 0.8 nW m–2 sr–1 at 3.6 and 4.5 μm to the diffuse cosmic infrared background (CIB). IRAC sources cannot contribute more than half of the total CIB flux estimated from DIRBE data. Barring an unexpected error in the DIRBE flux estimates, half the CIB flux must therefore come from a diffuse component.
[en] This study presents a search for infrared (IR) excess in the 3.4, 4.6, 12, and 22 μ m bands in a sample of 216 targets, composed of solar sibling, twin, and analog stars observed by the Wide-field Infrared Survey Explorer ( WISE ) mission. In general, an IR excess suggests the existence of warm dust around a star. We detected 12 μ m and/or 22 μ m excesses at the 3 σ level of confidence in five solar analog stars, corresponding to a frequency of 4.1% of the entire sample of solar analogs analyzed, and in one out of 29 solar sibling candidates, confirming previous studies. The estimation of the dust properties shows that the sources with IR excesses possess circumstellar material with temperatures that, within the uncertainties, are similar to that of the material found in the asteroid belt in our solar system. No photospheric flux excess was identified at the W1 (3.4 μ m) and W2 (4.6 μ m) WISE bands, indicating that, in the majority of stars of the present sample, no detectable dust is generated. Interestingly, among the 60 solar twin stars analyzed in this work, no WISE photospheric flux excess was detected. However, a null-detection excess does not necessarily indicate the absence of dust around a star because different causes, including dynamic processes and instrument limitations, can mask its presence.
[en] The article discusses the patterns of the polarization processes flowing in different types geo electric models under external electrical influence by the differential time mode, intended for direct measurements of the transitional characteristic second derivative of induced polarization at different configurations and parameters of the excitation. On the basis of the complex analysis of the characteristics of the amplitude time parameters of IP and the established regularities of the electrochemical charging of the geo electrical medium, are presented the main ways of the optimizing methods for performing such electrical prospecting studies
[en] The aim of true-amplitude imaging is to restore the amplitude information partially disappeared during different processing steps of the seismic data. In this paper, we try to develop a unified approach to the true-amplitude (TA) migration and partial migration (DMO) for two basic F-K and integral methods in 3D constant-offset data space. We, first, establish the connection between F-K and integral methods for TA migration in a 3D constant-offset medium. Secondly, we extend our analysis to unify the treatment of the TA migration and TA DMO within the same theoretical formulations for both F-K and integral approaches. Starting from the very general formulas obtained for F-K and integral methods in a 3D constant-offset environment, the amplitude preservation terms related to different acquisition configurations are derived as the special cases of the general formulation. Examples applied on synthetic and field data are given. Theoretical expectations are confirmed by the performance of the proposed method
[en] We present the preliminary analysis of 1023 known asteroids in the Hilda region of the solar system observed by the NEOWISE component of the Wide-field Infrared Survey Explorer (WISE). The sizes of the Hildas observed range from ∼3 to 200 km. We find no size-albedo dependency as reported by other projects. The albedos of our sample are low, with a weighted mean value of pV = 0.055 ± 0.018, for all sizes sampled by the NEOWISE survey. We observed a significant fraction of the objects in the two known collisional families in the Hilda population. It is found that the Hilda collisional family is brighter, with a weighted mean albedo of pV = 0.061 ± 0.011, than the general population and dominated by D-type asteroids, while the Schubart collisional family is darker, with a weighted mean albedo of pV = 0.039 ± 0.013. Using the reflected sunlight in the two shortest WISE bandpasses, we are able to derive a method for taxonomic classification of ∼10% of the Hildas detected in the NEOWISE survey. For the Hildas with diameter larger than 30 km, there are 67+7–15% D-type asteroids and 26+17–5% C-/P-type asteroids (with the majority of these being P-types).
[en] The Taurus Molecular Cloud subtends a large solid angle on the sky, in excess of 250 deg2. The search for legitimate Taurus members to date has been limited by sky coverage as well as the challenge of distinguishing members from field interlopers. The Wide-field Infrared Survey Explorer has recently observed the entire sky, and we take advantage of the opportunity to search for young stellar object (YSO) candidate Taurus members from a ∼260 deg2 region designed to encompass previously identified Taurus members. We use near- and mid-infrared colors to select objects with apparent infrared excesses and incorporate other catalogs of ancillary data to present a list of rediscovered Taurus YSOs with infrared excesses (taken to be due to circumstellar disks), a list of rejected YSO candidates (largely galaxies), and a list of 94 surviving candidate new YSO-like Taurus members. There is likely to be contamination lingering in this candidate list, and follow-up spectra are warranted.
[en] The Wide-field Infrared Survey Explorer has uncovered a population of young stellar objects (YSOs) in the Western Circinus molecular cloud. Images show the YSOs to be clustered into two main groups that are coincident with dark filamentary structure in the nebulosity. Analysis of photometry shows numerous Class I and II objects. The locations of several of these objects are found to correspond to known dense cores and CO outflows. Class I objects tend to be concentrated in dense aggregates, and Class II objects more evenly distributed throughout the region.
[en] The most challenging difficulty of streamer marine 4D seismic technology is repeating a given acquisition geometry with high precision. This challenge does not exist onshore, and it should then be possible to aim for higher 4D sensitivity needed to observe changes in carbonated reservoirs. The different categories of 4D noises are first examined and the focus is then given to the necessary positioning accuracy of source and receiver deployment. On synthetic data, it is demonstrated that the effect of positioning inaccuracy on 4D noise depends on ]apparent velocity. It is small on fast velocities, large on slow velocities. For this reason, it cannot be compensated for by application of a 1-D matching filter. Therefore, seismic positioning requirements must be re-assessed to increase land 4D sensitivity. A field experiment confirms the previous synthetic examples, leading to the conclusions oas follows:- A 1-m relative accuracy (difference between base and monitor) on the array's centre of gravity is adequate (but also necessary) if the frequency in the target area does not exceed 50 Hz, the dips are relatively small (less than (15) and a -20dB 4D noise is acceptable. Otherwise, relative accuracy requirements should be increased. -Moreover, in the process of ground roll, extreme care should be taken in repeating the arrays themselves. This second requirement is obviously easier to fulfill with simple and short arrays. This remark suggests that the conventional 50-m 3D group interval (and array size) may constitute another reason for the slow development of 4d seismic technology on land
[en] Complete text of publication follows. While high-degree global models of the gravity field have been produced for decades, the break-through for magnetic models has only been achieved in the last few years. This is primarily due to three reasons: (1) Long wavelength control for a global model requires highly accurate satellite measurements at low orbital altitudes. These have only recently become available with the ongoing CHAMP mission. (2) Due to the secular change of the Earth's core field, marine and airborne magnetic surveys have unknown offsets which make it difficult to integrate 60 years of surveys into a common global field model. (3) The geopotential can conveniently be inferred from measurements of the gravity acceleration by direct integration. In contrast, the magnetic potential is not completely determined by measurements of the anomaly of the total intensity, and it has to be estimated in an iterative scheme. Here, we present our modeling approach starting with the determination of the long-wavelength lithospheric field from CHAMP data then merging the marine and aeromagnetic data into the EMAG2 global magnetic anomaly grid which then provides the basis for the estimation of the NGDC-720 model (http://geomag.org).