2,662 research outputs found
A Bright Submillimeter Source in the Bullet Cluster (1E0657--56) Field Detected with BLAST
We present the 250, 350, and 500 micron detection of bright submillimeter
emission in the direction of the Bullet Cluster measured by the Balloon-borne
Large Aperture Submillimeter Telescope (BLAST). The 500 micron centroid is
coincident with an AzTEC 1.1 mm point-source detection at a position close to
the peak lensing magnification produced by the cluster. However, the 250 micron
and 350 micron centroids are elongated and shifted toward the south with a
differential shift between bands that cannot be explained by pointing
uncertainties. We therefore conclude that the BLAST detection is likely
contaminated by emission from foreground galaxies associated with the Bullet
Cluster. The submillimeter redshift estimate based on 250-1100 micron
photometry at the position of the AzTEC source is z_phot = 2.9 (+0.6 -0.3),
consistent with the infrared color redshift estimation of the most likely IRAC
counterpart. These flux densities indicate an apparent far-infrared luminosity
of L_FIR = 2E13 Lsun. When the amplification due to the gravitational lensing
of the cluster is removed, the intrinsic far-infrared luminosity of the source
is found to be L_FIR <= 10^12 Lsun, consistent with typical luminous infrared
galaxies.Comment: Accepted for publication in the Astrophysical Journal. Maps are
available at http://blastexperiment.info
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Evaluation of a new 12km regional perturbed parameter ensemble over Europe
We evaluate a 12-member perturbed parameter ensemble of regional climate simulations over Europe at 12km resolution, carried out as part of the UK Climate Projections (UKCP) project. This ensemble is formed by varying uncertain parameters within the model physics, allowing uncertainty in future projections due to climate modelling uncertainty to be explored in a systematic way. We focus on present day performance both compared to observations, and consistency with the driving global ensemble. Daily and seasonal temperature and precipitation are evaluated as two variables commonly used in impacts assessments. For precipitation we find that downscaling, even whilst within the convection-parameterised regime, generally improves daily precipitation, but not everywhere. In summer, the underestimation of dry day frequency is worse in the regional ensemble than in the driving simulations. For temperature we find that the regional ensemble inherits a large wintertime cold bias from the global model, however downscaling reduces this bias. The largest bias reduction is in daily winter cold temperature extremes.
In summer the regional ensemble is cooler and wetter than the driving global models, and we examine cloud and radiation diagnostics to understand the causes of the differences. We also use a low-resolution regional simulation to determine whether the differences are a consequence of resolution, or due to other configuration differences, with the predominant configuration difference being the treatment of aerosols. We find that use of the EasyAerosol scheme in the regional model, which aims to approximate the aerosol effects in the driving model, causes reduced temperatures by around 0.5K over Eastern Europe in Summer, and warming of a similar magnitude over France and Germany in Winter, relative to the impact of interactive aerosol in the global runs. Precipitation is also increased in these regions.
Overall, we find that the regional model is consistent with the global model, but with a typically better representation of daily extremes and consequently we have higher confidence in its projections of their future change
The BLAST View of the Star Forming Region in Aquila (ell=45deg,b=0deg)
We have carried out the first general submillimeter analysis of the field
towards GRSMC 45.46+0.05, a massive star forming region in Aquila. The
deconvolved 6 deg^2 (3\degree X 2\degree) maps provided by BLAST in 2005 at
250, 350, and 500 micron were used to perform a preliminary characterization of
the clump population previously investigated in the infrared, radio, and
molecular maps. Interferometric CORNISH data at 4.8 GHz have also been used to
characterize the Ultracompact HII regions (UCHIIRs) within the main clumps. By
means of the BLAST maps we have produced an initial census of the submillimeter
structures that will be observed by Herschel, several of which are known
Infrared Dark Clouds (IRDCs). Our spectral energy distributions of the main
clumps in the field, located at ~7 kpc, reveal an active population with
temperatures of T~35-40 K and masses of ~10^3 Msun for a dust emissivity index
beta=1.5. The clump evolutionary stages range from evolved sources, with
extended HII regions and prominent IR stellar population, to massive young
stellar objects, prior to the formation of an UCHIIR.The CORNISH data have
revealed the details of the stellar content and structure of the UCHIIRs. In
most cases, the ionizing stars corresponding to the brightest radio detections
are capable of accounting for the clump bolometric luminosity, in most cases
powered by embedded OB stellar clusters
BLAST05: Power Spectra of Bright Galactic Cirrus at Submillimeter Wavelengths
We report multi-wavelength power spectra of diffuse Galactic dust emission
from BLAST observations at 250, 350, and 500 microns in Galactic Plane fields
in Cygnus X and Aquila. These submillimeter power spectra statistically
quantify the self-similar structure observable over a broad range of scales and
can be used to assess the cirrus noise which limits the detection of faint
point sources. The advent of submillimeter surveys with the Herschel Space
Observatory makes the wavelength dependence a matter of interest. We show that
the observed relative amplitudes of the power spectra can be related through a
spectral energy distribution (SED). Fitting a simple modified black body to
this SED, we find the dust temperature in Cygnus X to be 19.9 +/- 1.3 K and in
the Aquila region 16.9 +/- 0.7 K. Our empirical estimates provide important new
insight into the substantial cirrus noise that will be encountered in
forthcoming observations.Comment: Submitted to the Astrophysical Journal. Maps and other data are
available at http://blastexperiment.info
Submillimeter Number Counts From Statistical Analysis of BLAST Maps
We describe the application of a statistical method to estimate submillimeter
galaxy number counts from confusion limited observations by the Balloon-borne
Large Aperture Submillimeter Telescope (BLAST). Our method is based on a
maximum likelihood fit to the pixel histogram, sometimes called 'P(D)', an
approach which has been used before to probe faint counts, the difference being
that here we advocate its use even for sources with relatively high
signal-to-noise ratios. This method has an advantage over standard techniques
of source extraction in providing an unbiased estimate of the counts from the
bright end down to flux densities well below the confusion limit. We
specifically analyse BLAST observations of a roughly 10 sq. deg. map centered
on the Great Observatories Origins Deep Survey South (GOODS-S) field. We
provide estimates of number counts at the three BLAST wavelengths, 250, 350,
and 500 microns; instead of counting sources in flux bins we estimate the
counts at several flux density nodes connected with power-laws. We observe a
generally very steep slope for the counts of about -3.7 at 250 microns and -4.5
at 350 and 500 microns, over the range ~0.02-0.5 Jy, breaking to a shallower
slope below about 0.015 Jy at all three wavelengths. We also describe how to
estimate the uncertainties and correlations in this method so that the results
can be used for model-fitting. This method should be well-suited for analysis
of data from the Herschel satellite.Comment: Accepted for publication in the Astrophysical Journal; see associated
data and other papers at http://blastexperiment.info
Deconvolution of Images from BLAST 2005: Insight into the K3-50 and IC 5146 Star-Forming Regions
We present an implementation of the iterative flux-conserving Lucy-Richardson
(L-R) deconvolution method of image restoration for maps produced by the
Balloon-borne Large Aperture Submillimeter Telescope (BLAST). We have analyzed
its performance and convergence extensively through simulations and
cross-correlations of the deconvolved images with available highresolution
maps. We present new science results from two BLAST surveys, in the Galactic
regions K3-50 and IC 5146, further demonstrating the benefits of performing
this deconvolution.
We have resolved three clumps within a radius of 4.'5 inside the star-forming
molecular cloud containing K3-50. Combining the well-resolved dust emission map
with available multi-wavelength data, we have constrained the Spectral Energy
Distributions (SEDs) of five clumps to obtain masses (M), bolometric
luminosities (L), and dust temperatures (T). The L-M diagram has been used as a
diagnostic tool to estimate the evolutionary stages of the clumps. There are
close relationships between dust continuum emission and both 21-cm radio
continuum and 12CO molecular line emission.
The restored extended large scale structures in the Northern Streamer of IC
5146 have a strong spatial correlation with both SCUBA and high resolution
extinction images. A dust temperature of 12 K has been obtained for the central
filament. We report physical properties of ten compact sources, including six
associated protostars, by fitting SEDs to multi-wavelength data. All of these
compact sources are still quite cold (typical temperature below ~ 16 K) and are
above the critical Bonner-Ebert mass. They have associated low-power Young
Stellar Objects (YSOs). Further evidence for starless clumps has also been
found in the IC 5146 region.Comment: 13 pages, 12 Figures, 3 Table
The BLAST Survey of the Vela Molecular Cloud: Physical Properties of the Dense Cores in Vela-D
The Balloon-borne Large-Aperture Submillimeter Telescope (BLAST) carried out
a 250, 350 and 500 micron survey of the galactic plane encompassing the Vela
Molecular Ridge, with the primary goal of identifying the coldest dense cores
possibly associated with the earliest stages of star formation. Here we present
the results from observations of the Vela-D region, covering about 4 square
degrees, in which we find 141 BLAST cores. We exploit existing data taken with
the Spitzer MIPS, IRAC and SEST-SIMBA instruments to constrain their
(single-temperature) spectral energy distributions, assuming a dust emissivity
index beta = 2.0. This combination of data allows us to determine the
temperature, luminosity and mass of each BLAST core, and also enables us to
separate starless from proto-stellar sources. We also analyze the effects that
the uncertainties on the derived physical parameters of the individual sources
have on the overall physical properties of starless and proto-stellar cores,
and we find that there appear to be a smooth transition from the pre- to the
proto-stellar phase. In particular, for proto-stellar cores we find a
correlation between the MIPS24 flux, associated with the central protostar, and
the temperature of the dust envelope. We also find that the core mass function
of the Vela-D cores has a slope consistent with other similar (sub)millimeter
surveys.Comment: Accepted for publication in the Astrophysical Journal. Data and maps
are available at http://blastexperiment.info
The Balloon-Borne Large Aperture Submillimeter Telescope (BLAST) 2005: A 10 deg^2 Survey of Star Formation in Cygnus X
We present Cygnus X in a new multi-wavelength perspective based on an
unbiased BLAST survey at 250, 350, and 500 micron, combined with rich datasets
for this well-studied region. Our primary goal is to investigate the early
stages of high mass star formation. We have detected 184 compact sources in
various stages of evolution across all three BLAST bands. From their
well-constrained spectral energy distributions, we obtain the physical
properties mass, surface density, bolometric luminosity, and dust temperature.
Some of the bright sources reaching 40 K contain well-known compact H II
regions. We relate these to other sources at earlier stages of evolution via
the energetics as deduced from their position in the luminosity-mass (L-M)
diagram. The BLAST spectral coverage, near the peak of the spectral energy
distribution of the dust, reveals fainter sources too cool (~ 10 K) to be seen
by earlier shorter-wavelength surveys like IRAS. We detect thermal emission
from infrared dark clouds and investigate the phenomenon of cold ``starless
cores" more generally. Spitzer images of these cold sources often show stellar
nurseries, but these potential sites for massive star formation are ``starless"
in the sense that to date there is no massive protostar in a vigorous accretion
phase. We discuss evolution in the context of the L-M diagram. Theory raises
some interesting possibilities: some cold massive compact sources might never
form a cluster containing massive stars; and clusters with massive stars might
not have an identifiable compact cold massive precursor.Comment: 42 pages, 31 Figures, 6 table
Callisto's Atmosphere and Its Space Environment: Prospects for the Particle Environment Package on Board JUICE
The JUpiter ICy moons Explorer (JUICE) of the European Space Agency will investigate Jupiter and its icy moons Europa, Ganymede, and Callisto, with the aim to better understand the origin and evolution of our Solar System and the emergence of habitable worlds around gas giants. The Particle Environment Package (PEP) on board JUICE is designed to measure neutrals and ions and electrons at thermal, suprathermal, and radiation belt energies (eV to MeV). In the vicinity of Callisto, PEP will characterize the plasma environment, the outer parts of Callisto's atmosphere and ionosphere and their interaction with Jupiter's dynamic magnetosphere. Roughly 20 Callisto flybys with closest approaches between 200 and 5,000 km altitude are planned over the course of the JUICE mission. In this article, we review the state of the art regarding Callisto's ambient environment and magnetospheric interaction with recent modeling efforts for Callisto's atmosphere and ionosphere. Based on this review, we identify science opportunities for the PEP observations to optimize scientific insight gained from the foreseen JUICE flybys. These considerations will inform both science operation planning of PEP and JUICE and they will guide future model development for Callisto's atmosphere, ionosphere, and their interaction with the plasma environment
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The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) 2006: Calibration and Flight Performance
The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) operated
successfully during a 250-hour flight over Antarctica in December 2006
(BLAST06). As part of the calibration and pointing procedures, the red
hypergiant star VY CMa was observed and used as the primary calibrator. Details
of the overall BLAST06 calibration procedure are discussed. The 1-sigma
absolute calibration is accurate to 10, 12, and 13% at the 250, 350, and 500
micron bands, respectively. The errors are highly correlated between bands
resulting in much lower error for the derived shape of the 250-500 micron
continuum. The overall pointing error is <5" rms for the 36, 42, and 60" beams.
The performance of the optics and pointing systems is discussed.Comment: Accepted for publication in the Astrophysical Journal. Maps available
at http://blastexperiment.info
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