14,866 research outputs found
The far-infrared/submillimeter properties of galaxies located behind the Bullet cluster
The Herschel Lensing Survey (HLS) takes advantage of gravitational lensing by massive galaxy clusters to sample a population of high-redshift galaxies which are too faint to be detected above the confusion limit of current far-infrared/submillimeter telescopes. Measurements from 100â500 ÎŒm bracket the peaks of the far-infrared spectral energy distributions of these galaxies, characterizing their infrared luminosities and star formation rates. We introduce initial results from our science demonstration phase observations, directed toward the Bullet cluster (1E0657-56). By combining our observations with LABOCA 870 ÎŒm and AzTEC 1.1 mm data we fully constrain the spectral energy distributions of 19 MIPS 24 ÎŒm-selected galaxies which are located behind the cluster. We find that their colors are best fit using templates based on local galaxies with systematically lower infrared luminosities. This suggests that our sources are not like local ultra-luminous infrared galaxies in which vigorous star formation is contained in a compact highly dust-obscured region. Instead, they appear to be scaled up versions of lower luminosity local galaxies with star formation occurring on larger physical scales
The Herschel Lensing Survey (HLS): Overview
The Herschel Lensing Survey (HLS) will conduct deep PACS and SPIRE imaging of âŒ40 massive clusters of galaxies. The strong gravitational lensing power of these clusters will enable us to penetrate through the confusion noise, which sets the ultimate limit on our ability to probe the
Universe with Herschel. Here we present an overview of our survey and a summary of the major results from our science demonstration phase (SDP) observations of the Bullet cluster (z = 0.297). The SDP data are rich and allow us to study not only the background high-redshift galaxies
(e.g., strongly lensed and distorted galaxies at z = 2.8 and 3.2) but also the properties of cluster-member galaxies. Our preliminary analysis shows a great diversity of far-infrared/submillimeter spectral energy distributions (SEDs), indicating that we have much to learn with Herschel about the properties of galaxy SEDs. We have also detected the Sunyaev-Zelâdovich (SZ) effect increment with the SPIRE data. The success of this SDP program demonstrates the great potential of the Herschel Lensing Survey to produce exciting results in a variety of science areas
Deep Herschel view of obscured star formation in the Bullet cluster
We use deep, five band (100â500 ÎŒm) data from the Herschel Lensing Survey (HLS) to fully constrain the obscured star formation rate, SFR_(FIR), of galaxies in the Bullet cluster (z = 0.296), and a smaller background system (z = 0.35) in the same field. Herschel detects 23 Bullet cluster members with a total SFRFIR = 144±14 M_â yr^(-1). On average, the background system contains brighter far-infrared (FIR) galaxies, with ~50% higher SFRFIR (21 galaxies; 207 ± 9 M_â yr^(-1)). SFRs extrapolated from 24 ÎŒm flux via recent templates (SFR_(24 ”m)) agree well with SFRFIR for ~60% of the cluster galaxies. In the remaining ~40%, SFR24 ”m underestimates SFR_(FIR) due to a significant excess in observed S_(100)/S_(24) (rest frame S_(75)/S_(18)) compared to templates of the same FIR luminosity
An \emph{ab initio} method for locating characteristic potential energy minima of liquids
It is possible in principle to probe the many--atom potential surface using
density functional theory (DFT). This will allow us to apply DFT to the
Hamiltonian formulation of atomic motion in monatomic liquids [\textit{Phys.
Rev. E} {\bf 56}, 4179 (1997)]. For a monatomic system, analysis of the
potential surface is facilitated by the random and symmetric classification of
potential energy valleys. Since the random valleys are numerically dominant and
uniform in their macroscopic potential properties, only a few quenches are
necessary to establish these properties. Here we describe an efficient
technique for doing this. Quenches are done from easily generated "stochastic"
configurations, in which the nuclei are distributed uniformly within a
constraint limiting the closeness of approach. For metallic Na with atomic pair
potential interactions, it is shown that quenches from stochastic
configurations and quenches from equilibrium liquid Molecular Dynamics (MD)
configurations produce statistically identical distributions of the structural
potential energy. Again for metallic Na, it is shown that DFT quenches from
stochastic configurations provide the parameters which calibrate the
Hamiltonian. A statistical mechanical analysis shows how the underlying
potential properties can be extracted from the distributions found in quenches
from stochastic configurations
Mid-infrared Variability from the Spitzer Deep Wide-field Survey
We use the multi-epoch, mid-infrared Spitzer Deep Wide-Field Survey to investigate the variability of objects in 8.1 deg^2 of the NOAO Deep Wide Field Survey Boötes field. We perform a Difference Image Analysis of the four available epochs between 2004 and 2008, focusing on the deeper 3.6 and 4.5 ÎŒm bands. Out of 474, 179 analyzed sources, 1.1% meet our standard variability selection criteria that the two light curves are strongly correlated (r > 0.8) and that their joint variance (Ï_(12)) exceeds that for all sources with the same magnitude by 2Ï. We then examine the mid-IR colors of the variable sources and match them with X-ray sources from the XBoötes survey, radio catalogs, 24 ÎŒm selected active galactic nucleus (AGN) candidates, and spectroscopically identified AGNs from the AGN and Galaxy Evolution Survey (AGES). Based on their mid-IR colors, most of the variable sources are AGNs (76%), with smaller contributions from stars (11%), galaxies (6%), and unclassified objects, although most of the stellar, galaxy, and unclassified sources are false positives. For our standard selection criteria, 11%-12% of the mid-IR counterparts to X-ray sources, 24 ÎŒm AGN candidates, and spectroscopically identified AGNs show variability. The exact fractions depend on both the search depth and the selection criteria. For example, 12% of the 1131 known z>1 AGNs in the field and 14%-17% of the known AGNs with well-measured fluxes in all four Infrared Array Camera bands meet our standard selection criteria. The mid-IR AGN variability can be well described by a single power-law structure function with an index of Îł â 0.5 at both 3.6 and 4.5 ÎŒm, and an amplitude of S _0 â 0.1 mag on rest-frame timescales of 2 yr. The variability amplitude is higher for shorter rest-frame wavelengths and lower luminosities
Thermal Kinetic Inductance Detectors for Millimeter-Wave Astrophysics
Thermal Kinetic Inductance Detectors (TKIDs) combine the excellent noise performance of traditional bolometers with a radio frequency (RF) multiplexing architecture that enables the large detector counts needed for the next generation of millimeter-wave instruments. Here we present dark prototype TKID pixels that demonstrate a noise equivalent power NEP = 2Ă10â»Âčâ·âW/Hz with a 1/f knee at 0.1 Hz, suitable for background-limited noise performance at 150 GHz from a ground-based site. We discuss the optimizations in the device design and fabrication techniques to realize optimal electrical performance and high quality factors at a bath temperature of 250 mK
Concurrent adaptation to opposing visual displacements during an alternating movement.
It has been suggested that, during tasks in which subjects are exposed to a visual rotation of cursor feedback, alternating bimanual adaptation to opposing rotations is as rapid as unimanual adaptation to a single rotation (Bock et al. in Exp Brain Res 162:513â519, 2005). However, that experiment did not test strict alternation of the limbs but short alternate blocks of trials. We have therefore tested adaptation under alternate left/right hand movement with opposing rotations. It was clear that the left and right hand, within the alternating conditions, learnt to adapt to the opposing displacements at a similar rate suggesting that two adaptive states were formed concurrently. We suggest that the separate limbs are used as contextual cues to switch between the relevant adaptive states. However, we found that during online correction the alternating conditions had a significantly slower rate of adaptation in comparison to the unimanual conditions. Control conditions indicate that the results are not directly due the alternation between limbs or to the constant switching of vision between the two eyes. The negative interference may originate from the requirement to dissociate the visual information of these two alternating displacements to allow online control of the two arms
Analysis of resonance multipoles from polarization observables in eta photoproduction
A combined analysis of new eta photoproduction data for total and
differential cross sections, target asymmetry and photon asymmetry is
presented. Using a few reasonable assumptions we perform the first
model-independent analysis of the E0+, E2- and M2- eta photoproduction
multipoles. Making use of the well-known A3/2 helicity amplitude of the
D13(1520) state we extract its branching ratio to the eta-N channel,
Gamma(eta,N)/Gamma = (0.08 +- 0.01)%. At higher energies, we show that the
photon asymmetry is extremely sensitive to small multipoles that are excited by
photons in the helicity 3/2 state. The new GRAAL photon asymmetry data at
higher energy show a clear signal of the F15(1680) excitation which permits
extracting an F15(1680)->eta,N branching ratio of (0.15 +0.35 -0.10)%.Comment: 14 pages of LATEX including 7 postscript figure
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