54 research outputs found
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
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
Over half of the far-infrared background light comes from galaxies at z >= 1.2
Submillimetre surveys during the past decade have discovered a population of
luminous, high-redshift, dusty starburst galaxies. In the redshift range 1 <= z
<= 4, these massive submillimetre galaxies go through a phase characterized by
optically obscured star formation at rates several hundred times that in the
local Universe. Half of the starlight from this highly energetic process is
absorbed and thermally re-radiated by clouds of dust at temperatures near 30 K
with spectral energy distributions peaking at 100 microns in the rest frame. At
1 <= z <= 4, the peak is redshifted to wavelengths between 200 and 500 microns.
The cumulative effect of these galaxies is to yield extragalactic optical and
far-infrared backgrounds with approximately equal energy densities. Since the
initial detection of the far-infrared background (FIRB), higher-resolution
experiments have sought to decompose this integrated radiation into the
contributions from individual galaxies. Here we report the results of an
extragalactic survey at 250, 350 and 500 microns. Combining our results at 500
microns with those at 24 microns, we determine that all of the FIRB comes from
individual galaxies, with galaxies at z >= 1.2 accounting for 70 per cent of
it. As expected, at the longest wavelengths the signal is dominated by
ultraluminous galaxies at z > 1.Comment: Accepted to Nature. Maps available at http://blastexperiment.info
BLAST: the Redshift Survey
The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) has recently
surveyed ~8.7 deg^2 centered on GOODS-South at 250, 350, and 500 microns. In
Dye et al. (2009) we presented the catalogue of sources detected at 5-sigma in
at least one band in this field and the probable counterparts to these sources
in other wavebands. In this paper, we present the results of a redshift survey
in which we succeeded in measuring redshifts for 82 of these counterparts. The
spectra show that the BLAST counterparts are mostly star-forming galaxies but
not extreme ones when compared to those found in the Sloan Digital Sky Survey.
Roughly one quarter of the BLAST counterparts contain an active nucleus. We
have used the spectroscopic redshifts to carry out a test of the ability of
photometric redshift methods to estimate the redshifts of dusty galaxies,
showing that the standard methods work well even when a galaxy contains a large
amount of dust. We have also investigated the cases where there are two
possible counterparts to the BLAST source, finding that in at least half of
these there is evidence that the two galaxies are physically associated, either
because they are interacting or because they are in the same large-scale
structure. Finally, we have made the first direct measurements of the
luminosity function in the three BLAST bands. We find strong evolution out to
z=1, in the sense that there is a large increase in the space-density of the
most luminous galaxies. We have also investigated the evolution of the
dust-mass function, finding similar strong evolution in the space-density of
the galaxies with the largest dust masses, showing that the luminosity
evolution seen in many wavebands is associated with an increase in the
reservoir of interstellar matter in galaxies.Comment: Accepted for publication in the Astrophysical Journal. Maps and
associated results are available at http://blastexperiment.info
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
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
BLAST Observations of the South Ecliptic Pole field: Number Counts and Source Catalogs
We present results from a survey carried out by the Balloon-borne Large
Aperture Submillimeter Telescope (BLAST) on a 9 deg^2 field near the South
Ecliptic Pole at 250, 350 and 500 {\mu}m. The median 1{\sigma} depths of the
maps are 36.0, 26.4 and 18.4 mJy, respectively. We apply a statistical method
to estimate submillimeter galaxy number counts and find that they are in
agreement with other measurements made with the same instrument and with the
more recent results from Herschel/SPIRE. Thanks to the large field observed,
the new measurements give additional constraints on the bright end of the
counts. We identify 132, 89 and 61 sources with S/N>4 at 250, 350, 500 {\mu}m,
respectively and provide a multi-wavelength combined catalog of 232 sources
with a significance >4{\sigma} in at least one BLAST band. The new BLAST maps
and catalogs are available publicly at http://blastexperiment.info.Comment: 25 pages, 6 figures, 4 tables, Accepted by ApJS. Maps and catalogs
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
A panchromatic study of BLAST counterparts: total star-formation rate, morphology, AGN fraction and stellar mass
We carry out a multi-wavelength study of individual galaxies detected by the
Balloon-borne Large Aperture Submillimeter Telescope (BLAST) and identified at
other wavelengths, using data spanning the radio to the ultraviolet (UV). We
develop a Monte Carlo method to account for flux boosting, source blending, and
correlations among bands, which we use to derive deboosted far-infrared (FIR)
luminosities for our sample. We estimate total star-formation rates for BLAST
counterparts with z < 0.9 by combining their FIR and UV luminosities. Star
formation is heavily obscured at L_FIR > 10^11 L_sun, z > 0.5, but the
contribution from unobscured starlight cannot be neglected at L_FIR < 10^11
L_sun, z < 0.25. We assess that about 20% of the galaxies in our sample show
indication of a type-1 active galactic nucleus (AGN), but their submillimeter
emission is mainly due to star formation in the host galaxy. We compute stellar
masses for a subset of 92 BLAST counterparts; these are relatively massive
objects, with a median mass of ~10^11 M_sun, which seem to link the 24um and
SCUBA populations, in terms of both stellar mass and star-formation activity.
The bulk of the BLAST counterparts at z<1 appear to be run-of-the-mill
star-forming galaxies, typically spiral in shape, with intermediate stellar
masses and practically constant specific star-formation rates. On the other
hand, the high-z tail of the BLAST counterparts significantly overlaps with the
SCUBA population, in terms of both star-formation rates and stellar masses,
with observed trends of specific star-formation rate that support strong
evolution and downsizing.Comment: Accepted for publication in the Astrophysical Journal. 44 pages, 11
figures. The SED template for the derivation of L_FIR has changed (added new
figure) and the discussion on the stellar masses has been improved. The
complete set of full-color postage-stamps can be found at
http://blastexperiment.info/results_images/moncelsi
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