3,553 research outputs found
Observations from Preliminary Experiments on Spatial and Temporal Pressure Measurements from Near-Field Free Air Explosions
It is self-evident that a crucial step in analysing the performance of protective structures is to be able to accurately quantify the blast load arising from a high explosive detonation. For structures located near to the source of a high explosive detonation, the resulting pressure is extremely high in magnitude and highly non-uniform over the face of the target. There exists very little direct measurement of blast parameters in the nearfield, mainly attributed to the lack of instrumentation sufficiently robust to survive extreme loading events yet sensitive enough to capture salient features of the blast. Instead literature guidance is informed largely by early numerical analyses and parametric studies. Furthermore, the lack of an accurate, reliable data set has prevented subsequent numerical analyses from being validated against experimental trials. This paper presents an experimental methodology that has been developed in part to enable such experimental data to be gathered. The experimental apparatus comprises an array of Hopkinson pressure bars, fitted through holes in a target, with the loaded faces of the bars flush with the target face. Thus, the bars are exposed to the normally or obliquely reflected shocks from the impingement of the blast wave with the target. Pressure-time recordings are presented along with associated Arbitary-Langrangian-Eulerian modelling using the LS-DYNA explicit numerical code. Experimental results are corrected for the effects of dispersion of the propagating waves in the pressure bars, enabling accurate characterisation of the peak pressures and impulses from these loadings. The combined results are used to make comments on the mechanism of the pressure load for very near-field blast events
Spitzer and Hubble Constraints on the Physical Properties of the z~7 Galaxy Strongly Lensed by Abell 2218
We report the detection of a z~7 galaxy strongly lensed by the massive galaxy
cluster Abell 2218 (z=0.175) at 3.6 and 4.5 um using the Spitzer Observatory
and at 1.1 um using the Hubble Space Telescope. The new data indicate a refined
photometric redshift in the range of 6.6-6.8 depending on the presence of
Ly-alpha emission. The spectral energy distribution is consistent with having a
significant Balmer break, suggesting that the galaxy is in the poststarburst
stage with an age of at least ~50 Myr and quite possibly a few hundred Myr.
This suggests the possibility that a mature stellar population is already in
place at such a high redshift. Compared with typical Lyman break galaxies at
z~3-4, the stellar mass is an order of magnitude smaller (~10^{9} Msun), but
the specific star formation rate (star formation rate/M_{star}) is similarly
large (> 10^{-9} yr^{-1}), indicating equally vigorous star-forming activity.Comment: 11 pages, 2 figures, 2 tables; Accepted for publication in ApJ
A z = 2.5 protocluster associated with the radio galaxy MRC 2104-242: star formation and differing mass functions in dense environments
We present results from a narrow-band survey of the field around the high-redshift radio galaxy MRC 2104â242. We have selected Hα emitters in a 7 arcmin2 field and compared the measured number density with that of a field sample at similar redshift. We find that MRC 2104â242 lies in an overdensity of galaxies that is 8.0 ± 0.8 times the average density of a blank field, suggesting it resides in a large-scale structure that may eventually collapse to form a massive cluster. We find that there is more dust obscured star formation in the protocluster galaxies than in similarly selected control field galaxies and there is tentative evidence of a higher fraction of starbursting galaxies in the denser environment. However, on average we do not find a difference between the star formation rate (SFR)âmass relations of the protocluster and field galaxies and so conclude that the SFR of these galaxies at z ⌠2.5 is governed predominantly by galaxy mass and not the host environment. We also find that the stellar mass distribution of the protocluster galaxies is skewed towards higher masses and there is a significant lack of galaxies at M 1010.5M_) galaxies, the density of the protocluster field increases to âŒ55 times the control field density
Species of ground beetle (Coleoptera: Carabidae) in organic apple orchards of British Columbia
In a two year study, 14 genera of Carabidae (Agonum Bonelli, Amara Bonelli, Anisodactylus Dejean, Bembidion Latreille, Carabus Linné, Harpalus Latreille, Lebia Latreille, Loricera Latreille, Poecilus Bonelli, Pterostichus Bonelli, Scaphinotus Dejean, Stenolophus Stephens, Syntomus Hope and Trechus Clairville) represented by 44 species were identified from six commercial organic apple orchards in the southern Similkameen valley in British Columbia, Canada; 13 of these species were not native to the area. The 4,299 specimens were caught in 'ramp' pitfall traps, with the genera Pterostichus and Harpalus comprising 56% and 43%, respectively. Numbers of Carabidae ranged from 11-21 species per orchard, with their presence detected throughout the collection period
Spatially Resolved Outflows in a Seyfert Galaxy at z = 2.39
We present the first spatially resolved analysis of rest-frame optical and UV
imaging and spectroscopy for a lensed galaxy at z = 2.39 hosting a Seyfert
active galactic nucleus (AGN). Proximity to a natural guide star has enabled
high signal-to-noise VLT SINFONI + adaptive optics observations of rest-frame
optical diagnostic emission lines, which exhibit an underlying broad component
with FWHM ~ 700 km/s in both the Balmer and forbidden lines. Measured line
ratios place the outflow robustly in the region of the ionization diagnostic
diagrams associated with AGN. This unique opportunity - combining gravitational
lensing, AO guiding, redshift, and AGN activity - allows for a magnified view
of two main tracers of the physical conditions and structure of the
interstellar medium in a star-forming galaxy hosting a weak AGN at cosmic noon.
By analyzing the spatial extent and morphology of the Ly-alpha and
dust-corrected H-alpha emission, disentangling the effects of star formation
and AGN ionization on each tracer, and comparing the AGN induced mass outflow
rate to the host star formation rate, we find that the AGN does not
significantly impact the star formation within its host galaxy.Comment: 16 pages, 5 figures, accepted for publication in Ap
SGAS 143845.1+145407: A Big, Cool Starburst at Redshift 0.816
We present the discovery and a detailed multi-wavelength study of a
strongly-lensed luminous infrared galaxy at z=0.816. Unlike most known lensed
galaxies discovered at optical or near-infrared wavelengths this lensed source
is red, r-Ks = 3.9 [AB], which the data presented here demonstrate is due to
ongoing dusty star formation. The overall lensing magnification (a factor of
17) facilitates observations from the blue optical through to 500micron, fully
capturing both the stellar photospheric emission as well as the re-processed
thermal dust emission. We also present optical and near-IR spectroscopy. These
extensive data show that this lensed galaxy is in many ways typical of
IR-detected sources at z~1, with both a total luminosity and size in accordance
with other (albeit much less detailed) measurements in samples of galaxies
observed in deep fields with the Spitzer telescope. Its far-infrared spectral
energy distribution is well-fit by local templates that are an order of
magnitude less luminous than the lensed galaxy; local templates of comparable
luminosity are too hot to fit. Its size (D~7kpc) is much larger than local
luminous infrared galaxies, but in line with sizes observed for such galaxies
at z~1. The star formation appears uniform across this spatial scale. In this
source, the luminosity of which is typical of sources that dominate the cosmic
infrared background, we find that star formation is spatially extended and well
organised, quite unlike the compact merger-driven starbursts which are typical
for sources of this luminosity at z~0.Comment: 18 pages, 10 figure
Extremely Red Objects in The Lockman Hole
We investigate Extremely Red Objects (EROs) using near- and mid-infrared
observations in five passbands (3.6 to 24 micron) obtained from the Spitzer
Space Telescope, and deep ground-based R and K imaging. The great sensitivity
of the IRAC camera allows us to detect 64 EROs in only 12 minutes of IRAC
exposure time, by means of an R-[3.6] color cut (analogous to the traditional
red R-K cut). A pure infrared K-[3.6] red cut detects a somewhat different
population and may be more effective at selecting z > 1.3 EROs. We find 17% of
all galaxies detected by IRAC at 3.6 or 4.5 micron to be EROs. These
percentages rise to about 40% at 5.8 micron, and about 60% at 8.0 micron. We
utilize the spectral bump at 1.6 micron to divide the EROs into broad redshift
slices using only near-infrared colors (2.2/3.6/4.5 micron). We conclude that
two-thirds of all EROs lie at redshift z > 1.3. Detections at 24 micron imply
that at least 11% of 0.6 1.3 EROs are
dusty star-forming galaxies.Comment: to appear in the special Spitzer issue of the ApJ
A search for debris disks in the Herschel-ATLAS
Original article can be found at: http://www.aanda.org/ Copyright The European Southern Observatory (ESO)Aims. We aim to demonstrate that the Herschel-ATLAS (H-ATLAS) is suitable for a blind and unbiased survey for debris disks by identifying candidate debris disks associated with main sequence stars in the initial science demonstration field of the survey. We show that H-ATLAS reveals a population of far-infrared/sub-mm sources that are associated with stars or star-like objects on the SDSS main-sequence locus. We validate our approach by comparing the properties of the most likely candidate disks to those of the known population. Methods. We use a photometric selection technique to identify main sequence stars in the SDSS DR7 catalogue and a Bayesian Likelihood Ratio method to identify H-ATLAS catalogue sources associated with these main sequence stars. Following this photometric selection we apply distance cuts to identify the most likely candidate debris disks and rule out the presence of contaminating galaxies using UKIDSS LAS K-band images. Results. We identify 78 H-ATLAS sources associated with SDSS point sources on the main-sequence locus, of which two are the most likely debris disk candidates: H-ATLAS J090315.8 and H-ATLAS J090240.2. We show that they are plausible candidates by comparing their properties to the known population of debris disks. Our initial results indicate that bright debris disks are rare, with only 2 candidates identified in a search sample of 851 stars. We also show that H-ATLAS can derive useful upper limits for debris disks associated with Hipparcos stars in the field and outline the future prospects for our debris disk search programme.Peer reviewe
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