737 research outputs found
The Canada-UK Deep Submillimetre Survey: First Submillimetre Images, the Source Counts, and Resolution of the Background
We present the first results of a deep unbiased submillimetre survey carried
out at 450 and 850 microns. We detected 12 sources at 850 microns, giving a
surface density of sources with 850-micron flux densities > 2.8mJy of of
0.49+-0.16 per square arcmin. The sources constitute 20-30% of the background
radiation at 850 microns and thus a significant fraction of the entire
background radiation produced by stars. This implies, through the connection
between metallicity and background radiation, that a significant fraction of
all the stars that have ever been formed were formed in objects like those
detected here. The combination of their large contribution to the background
radiation and their extreme bolometric luminosities make these objects
excellent candidates for being proto-ellipticals. Optical astronomers have
recently shown that the UV-luminosity density of the universe increases by a
factor of about 10 between z=0 and z=1 and then decreases again at higher
redshifts. Using the results of a parallel submillimetre survey of the local
universe, we show that both the submillimetre source density and background can
be explained if the submillimetre luminosity density evolves in a similar way
to the UV-luminosity density. Thus, if these sources are ellipticals in the
process of formation, they may be forming at relatively modest redshifts.Comment: 8 pages (LATEX), 6 postscript figures, submitted to ApJ Letter
Cold Dust in Kepler's Supernova Remnant
The timescales to replenish dust from the cool, dense winds of Asymptotic
Giant Branch stars are believed to be greater than the timescales for dust
destruction. In high redshift galaxies, this problem is further compounded as
the stars take longer than the age of the Universe to evolve into the dust
production stages. To explain these discrepancies, dust formation in supernovae
(SNe) is required to be an important process but until very recently dust in
supernova remnants has only been detected in very small quantities. We present
the first submillimeter observations of cold dust in Kepler's supernova remnant
(SNR) using SCUBA. A two component dust temperature model is required to fit
the Spectral Energy Distribution (SED) with K and K. The total mass of dust implied for Kepler is -
1000 times greater than previous estimates. Thus SNe, or their progenitors may
be important dust formation sites.Comment: 12 pages, 2 figures, accepted to ApJL, corrected proof
The SCUBA Local Universe Galaxy Survey I: First Measurements of the Submillimetre Luminosity and Dust Mass Functions
We have used SCUBA to observe a complete sample of 104 galaxies selected at
60 microns from the IRAS BGS and we present here the 850 micron measurements.
Fitting the 60,100 and 850 micron fluxes with a single temperature dust model
gives the sample mean temperature T=36 K and beta = 1.3. We do not rule out the
possibility of dust which is colder than this, if a 20 K component was present
then our dust masses would increase by factor 1.5-3. We present the first
measurements of the luminosity and dust mass functions, which were well fitted
by Schechter functions (unlike those 60 microns). We have correlated many
global galaxy properties with the submillimetre and find that there is a
tendancy for less optically luminous galaxies to contain warmer dust and have
greater star formation efficiencies (cf. Young 1999). The average gas-to-dust
ratio for the sample is 581 +/- 43 (using both atomic and molecular hydrogen),
significantly higher than the Galactic value of 160. We believe this
discrepancy is due to a cold dust component at T < 20 K. There is a suprisingly
tight correlation between dust mass and the mass of molecular hydrogen as
estimated from CO measurements, with an intrinsic scatter of ~50%.Comment: 24 pages, 15 figures, 8 tables, accepted for publication in MNRA
The Canada-UK Deep Submillimetre Survey: The Survey of the 14-hour field
We have used SCUBA to survey an area of 50 square arcmin, detecting 19
sources down to a 3sigma sensitivity limit of 3.5 mJy at 850 microns. We have
used Monte-Carlo simulations to assess the effect of source confusion and noise
on the SCUBA fluxes and positions, finding that the fluxes of sources in the
SCUBA surveys are significantly biased upwards and that the fraction of the 850
micron background that has been resolved by SCUBA has been overestimated. The
radio/submillmetre flux ratios imply that the dust in these galaxies is being
heated by young stars rather than AGN. We have used simple evolution models
based on our parallel SCUBA survey of the local universe to address the major
questions about the SCUBA sources: (1) what fraction of the star formation at
high redshift is hidden by dust? (2) Does the submillimetre luminosity density
reach a maximum at some redshift? (3) If the SCUBA sources are
proto-ellipticals, when exactly did ellipticals form? However, we show that the
observations are not yet good enough for definitive answers to these questions.
There are, for example, acceptable models in which 10 times as much
high-redshift star formation is hidden by dust as is seen at optical
wavelengths, but also acceptable ones in which the amount of hidden star
formation is less than that seen optically. There are acceptable models in
which very little star formation occurred before a redshift of three (as might
be expected in models of hierarchical galaxy formation), but also ones in which
30% of the stars have formed by this redshift. The key to answering these
questions are measurements of the dust temperatures and redshifts of the SCUBA
sources.Comment: 41 pages (latex), 17 postscript figures, to appear in the November
issue of the Astronomical Journa
Comparison of absolute gain photometric calibration between Planck/HFI and Herschel/SPIRE at 545 and 857 GHz
We compare the absolute gain photometric calibration of the Planck/HFI and
Herschel/SPIRE instruments on diffuse emission. The absolute calibration of HFI
and SPIRE each relies on planet flux measurements and comparison with
theoretical far-infrared emission models of planetary atmospheres. We measure
the photometric cross calibration between the instruments at two overlapping
bands, 545 GHz / 500 m and 857 GHz / 350 m. The SPIRE maps used have
been processed in the Herschel Interactive Processing Environment (Version 12)
and the HFI data are from the 2015 Public Data Release 2. For our study we used
15 large fields observed with SPIRE, which cover a total of about 120 deg^2. We
have selected these fields carefully to provide high signal-to-noise ratio,
avoid residual systematics in the SPIRE maps, and span a wide range of surface
brightness. The HFI maps are bandpass-corrected to match the emission observed
by the SPIRE bandpasses. The SPIRE maps are convolved to match the HFI beam and
put on a common pixel grid. We measure the cross-calibration relative gain
between the instruments using two methods in each field, pixel-to-pixel
correlation and angular power spectrum measurements. The SPIRE / HFI relative
gains are 1.047 ( 0.0069) and 1.003 ( 0.0080) at 545 and 857 GHz,
respectively, indicating very good agreement between the instruments. These
relative gains deviate from unity by much less than the uncertainty of the
absolute extended emission calibration, which is about 6.4% and 9.5% for HFI
and SPIRE, respectively, but the deviations are comparable to the values 1.4%
and 5.5% for HFI and SPIRE if the uncertainty from models of the common
calibrator can be discounted. Of the 5.5% uncertainty for SPIRE, 4% arises from
the uncertainty of the effective beam solid angle, which impacts the adopted
SPIRE point source to extended source unit conversion factor (Abridged)Comment: 13 pages, 10 figures; Incorporates revisions in response to referee
comments; cross calibration factors unchange
The Canada-UK Deep Submillimeter Survey VI: The 3-Hour Field
We present the complete submillimeter data for the Canada-UK Deep
Submillimeter Survey (CUDSS) 3-hour field. The obeservations were taken with
the Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk
Maxwell Telescope on Mauna Kea. The 3-hour field is one of two main fields in
our survey and covers 60 square arcminutes to a 3-sigma depth of 3 mJy. In this
field we have detected 27 sources above 3-sigma and 15 above 3.5-sigma. We
assume the source counts follow the form and
measure = 3.3. This is in good agreement with previous
studies and further supports our claim (Eales et al., 2000) that SCUBA sources
brighter than 3 mJy produce ~20% of the 850m background energy. Using
preliminary ISO 15 m maps and VLA 1.4 GHz data we have identified
counterparts for six objects and have marginal detections at 450m for two
additional sources. With this information we estimate a median redshift for the
sample of 2.00.5, with 10% lying at 1. We have measured the
angular clustering of S850 > 3 mJy sources using the source catalogues from the
CUDSS two main fields, the 3-hour and 14-hour fields, and find a marginal
detection of clustering, primarily from the 14-hour field, of
. This is consistent with clustering at
least as strong as that seen for the Lyman-break galaxy population and the
Extremely Red Objects. Since SCUBA sources are selected over a broader range in
redshifts than these two populations the strength of the true spatial
clustering is expected to be correspondingly stronger.Comment: 17 pages, 8 figures, submitted to Ap
Tunable-filter imaging of quasar fields at z~1. I. A cluster around MRC B0450-221
Using a combination of multicolour broad- and narrow-band imaging techniques
and follow-up spectroscopy, we have detected an overdensity of galaxies in the
field of quasar MRC B0450-221, whose properties are consistent with a cluster
at the quasar redshift z=0.9. An excess of red galaxies (V-I>2.2, I-K'>3.8) is
evident within 1' of the quasar, with the colours expected for galaxies at
z=0.9 that have evolved passively for 3 Gyr or more. A number of line-emitting
galaxies (nine candidates with equivalent widths EW>70A) are also detected in
the field using the TAURUS Tunable Filter (TTF). Three have been confirmed
spectroscopically to indeed lie at z=0.9. The TTF candidates with the strongest
[O II] line emission cluster in a group which lies 200-700 kpc away from the
quasar and the red galaxy excess, and therefore most likely on the outskirts of
the cluster. These observations are the first in a series probing quasar
environments at z~1 with TTF.Comment: Accepted for publication in AJ. 25 pages, 24 figs (large files in jpg
or gif format), uses emulateapj.st
Far-infrared spectroscopy of a lensed starburst: a blind redshift from Herschel
We report the redshift of HATLAS J132427.0+284452 (hereafter HATLAS J132427),
a gravitationally lensed starburst galaxy, the first determined 'blind' by the
Herschel Space Observatory. This is achieved via the detection of [C II]
consistent with z = 1.68 in a far-infrared spectrum taken with the SPIRE
Fourier Transform Spectrometer. We demonstrate that the [C II] redshift is
secure via detections of CO J = 2 - 1 and 3 - 2 using the Combined Array for
Research in Millimeter-wave Astronomy and the Institut de Radioastronomie
Millimetrique's Plateau de Bure Interferometer. The intrinsic properties appear
typical of high-redshift starbursts despite the high lensing-amplified fluxes,
proving the ability of the FTS to probe this population with the aid of
lensing. The blind detection of [C II] demonstrates the potential of the SAFARI
imaging spectrometer, proposed for the much more sensitive SPICA mission, to
determine redshifts of multiple dusty galaxies simultaneously without the
benefit of lensing.Comment: 6 pages, 5 figures, accepted for publication in MNRAS as a Lette
Young stars and non-stellar emission in the aligned radio galaxy 3C 256
We present ground-based images of the z=1.824 radio galaxy 3C 256 in the
standard BVRIJHK filters and an interference filter centered at 8800A, a Hubble
Space Telescope image in a filter dominated by Ly-alpha emission (F336W), and
spectra covering rest-frame wavelengths from Ly-alpha to [O III] 5007. Together
with published polarimetry observations, we use these to decompose the overall
spectral energy distribution into nebular continuum emission, scattered quasar
light, and stellar emission. The nebular continuum and scattered light together
comprise half (one third) of the V-band (K-band) light within a 4-arcsec
aperture, and are responsible for the strong alignment between the
optical/near-infrared light and the radio emission. The stellar emission is
dominated by a population estimated to be 100-200 Myr old (assuming a Salpeter
IMF), and formed in a short burst with a peak star formation rate of 1-4x10^3
Msun/yr. The total stellar mass is estimated to be no more than 2x10^{11} Msun,
which is far less than other luminous radio galaxies at similar redshifts, and
suggests that 3C 256 will undergo further star formation or mergers.Comment: 35 pages including 10 figures; to appear in Nov 10 Ap
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