1,870 research outputs found
A 3D Drizzle Algorithm for JWST and Practical Application to the MIRI Medium Resolution Spectrometer
We describe an algorithm for application of the classic `drizzle' technique
to produce 3d spectral cubes using data obtained from the slicer-type integral
field unit (IFU) spectrometers on board the James Webb Space Telescope. This
algorithm relies upon the computation of overlapping volume elements (composed
of two spatial dimensions and one spectral dimension) between the 2d detector
pixels and the 3d data cube voxels, and is greatly simplified by treating the
spatial and spectral overlaps separately at the cost of just 0.03% in
spectrophotometric fidelity. We provide a matrix-based formalism for the
computation of spectral radiance, variance, and covariance from arbitrarily
dithered data and comment on the performance of this algorithm for the
Mid-Infrared Instrument's Medium Resolution IFU Spectrometer (MIRI MRS). We
derive a series of simplified scaling relations to account for covariance
between cube spaxels in spectra extracted from such cubes, finding
multiplicative factors ranging from 1.5 to 3 depending on the wavelength range
and kind of data cubes produced. Finally, we discuss how undersampling produces
periodic amplitude modulations in the extracted spectra in addition to those
naturally produced by fringing within the instrument; reducing such
undersampling artifacts below 1% requires a 4-point dithering strategy and
spectral extraction radii of 1.5 times the PSF FWHM or greater.Comment: 16 pages, 12 figures. Revised version resubmitted to A
The discovery of the most UV-Lya luminous star-forming galaxy: a young, dust- and metal-poor starburst with QSO-like luminosities
We report the discovery of BOSS-EUVLG1 at z=2.469, by far the most luminous,
almost un-obscured star-forming galaxy known at any redshift. First classified
as a QSO within the Baryon Oscillation Spectroscopic Survey, follow-up
observations with the Gran Telescopio Canarias reveal that its large
luminosity, MUV = -24.40 and log(L_Lya/erg s-1) = 44.0, is due to an intense
burst of star-formation, and not to an AGN or gravitational lensing.
BOSS-EUVLG1 is a compact (reff = 1.2 kpc), young (4-5 Myr) starburst with a
stellar mass log(M*/Msun) = 10.0 +/- 0.1 and a prodigious star formation rate
of ~1000 Msun yr-1. However, it is metal- and dust-poor (12+log(O/H) = 8.13 +/-
0.19, E(B-V) = 0.07, log(LIR/LUV) < -1.2), indicating that we are witnessing
the very early phase of an intense starburst that has had no time to enrich the
ISM. BOSS-EUVLG1 might represent a short-lived (<100 Myrs), yet important phase
of star-forming galaxies at high redshift that has been missed in previous
surveys. Within a galaxy evolutionary scheme, BOSS-EUVLG1 could likely
represent the very initial phases in the evolution of massive quiescent
galaxies, even before the dusty star-forming phase.Comment: 6 pages, 3 figures, 1 table. Accepted for publication in MNRAS
Letter
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
The Pierre Auger Observatory III: Other Astrophysical Observations
Astrophysical observations of ultra-high-energy cosmic rays with the Pierre
Auger ObservatoryComment: Contributions to the 32nd International Cosmic Ray Conference,
Beijing, China, August 201
Mechanical Activation of Al-Oxyhydroxide Minerals â Physicochemical Changes, Reactivity and Relevance to Bayer Process
Overview of our research on âstructure and reactivityâ of gibbsite and boehmite under varied conditions of mechanical activation, e.g. milling energy and presence of a second phase is presented. Bulk and surface changes induced in the solids by milling are characterized in terms of morphology, particle size distribution, specific surface area and nature of porosity, crystallite size and zeta potential. Results on enhanced amorphisation of gibbsite in presence of a second phase (quartz, hematite etc), changes in zeta potential of gibbsite due to loss of texture during milling and anomalous decrease in surface area of boehmite during milling are reported. Reactivity of the activated solids in sodium hydroxide and variation in thermal transformation temperatures is correlated with physicochemical characteristics of the samples and plausible explanation for the observed correlations presented. Significance of the results with specific reference to bauxite and alumina processing in Bayer process is highlighted
Measurement of the Depth of Maximum of Extensive Air Showers above 10^18 eV
We describe the measurement of the depth of maximum, Xmax, of the
longitudinal development of air showers induced by cosmic rays. Almost four
thousand events above 10^18 eV observed by the fluorescence detector of the
Pierre Auger Observatory in coincidence with at least one surface detector
station are selected for the analysis. The average shower maximum was found to
evolve with energy at a rate of (106 +35/-21) g/cm^2/decade below 10^(18.24 +/-
0.05) eV and (24 +/- 3) g/cm^2/decade above this energy. The measured
shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2. The
interpretation of these results in terms of the cosmic ray mass composition is
briefly discussed.Comment: Accepted for publication by PR
Operations of and Future Plans for the Pierre Auger Observatory
Technical reports on operations and features of the Pierre Auger Observatory,
including ongoing and planned enhancements and the status of the future
northern hemisphere portion of the Observatory. Contributions to the 31st
International Cosmic Ray Conference, Lodz, Poland, July 2009.Comment: Contributions to the 31st ICRC, Lodz, Poland, July 200
Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory
The Pierre Auger Collaboration has reported evidence for anisotropy in the
distribution of arrival directions of the cosmic rays with energies
eV. These show a correlation with the distribution
of nearby extragalactic objects, including an apparent excess around the
direction of Centaurus A. If the particles responsible for these excesses at
are heavy nuclei with charge , the proton component of the
sources should lead to excesses in the same regions at energies . We here
report the lack of anisotropies in these directions at energies above
(for illustrative values of ). If the anisotropies
above are due to nuclei with charge , and under reasonable
assumptions about the acceleration process, these observations imply stringent
constraints on the allowed proton fraction at the lower energies
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