1,152 research outputs found
Upper limits on K-band polarization in three high-redshift radio galaxies: LBDS 53W091, 3C 441 and MRC 0156-252
We present the results of K-band imaging polarimetry of three radio galaxies,
including the very red and apparently old z=1.55 galaxy 53W091. We find weak
evidence for polarization in components of 3C 441 and in the south-east
companion of 53W091, but no evidence of significant polarization in 53W091
itself. We also find strong evidence that MRC 0156-252 is unpolarised. We
present upper limits for the K-band polarization of all three sources. For
53W091, the lack of significant K-band polarization provides further confidence
that its red R-K colour can be attributed to a mature stellar population,
consistent with the detailed analyses of its ultraviolet spectral-energy
distribution which indicate a minimum age of 2-3.5 Gyr.Comment: 7 pages, 3 postscript figures. In press at MNRA
Mapping the interstellar medium in galaxies with Herschel/SPIRE
The standard method of mapping the interstellar medium in a galaxy, by observing the molecular gas in the CO 1-0 line and the atomic gas in the 21-cm line, is largely limited with current telescopes to galaxies in the nearby universe. In this letter, we use SPIRE observations of the galaxies
M99 and M100 to explore the alternative approach of mapping the interstellar medium using the continuum emission from the dust. We have compared the methods by measuring the relationship between the star-formation rate and the surface density of gas in the galaxies using both
methods. We find the two methods give relationships with a similar dispersion, confirming that observing the continuum emission from the dust is a promising method of mapping the interstellar medium in galaxies
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
The Linear-Size Evolution of Classical Double Radio Sources
Recent investigations of how the median size of extragalactic radio sources
change with redshift have produced inconsistent results. Eales compared the
radio and optical properties of a bright 3C and faint 6C sample and concluded
that (), with being the median
size of the radio sources at a given epoch and z the redshift. Oort, Katgert,
and Windhorst, on the other hand, from a comparison of the properties of a
number of radio samples, found much stronger evolution, with
. In this paper we attempt to resolve the
difference. We have repeated the analysis of Eales using the virtually complete
redshift information that now exists for the 6C sample. Confining our analysis
to FR2 sources, which we argue is the best-understood class of radio sources
and the least likely to be affected by selection effects, we find
() and
(). Our complete redshift information allows us to gain insight
into our result by plotting a radio luminosity-size (P-D) diagram for the 6C
sample. The most obvious difference between the 3C and 6C P-D diagrams is the
clump of sources in the 6C diagram at . These clump sources have similar sizes to the emission-line
regions found around high-redshift radio galaxies, suggesting that the presence
of dense line-emitting gas around high-redshift radio galaxies is responsible
for the size evolution. We show that this explanation can quantitatively
explain the observed size evolution, as long as there is either little X-ray
emitting gas around these objects or, if there is, it is distributed in a
similar way to the emission-line gas: highly anisotropic and inhomogeneous.Comment: compressed and uuencoded postscript file. 33 pages including 5
figures (441951 bytes). Accepted for publication in September Ap
Radio Galaxy Clustering at z~0.3
Radio galaxies are uniquely useful as probes of large-scale structure as
their uniform identification with giant elliptical galaxies out to high
redshift means that the evolution of their bias factor can be predicted. As the
initial stage in a project to study large-scale structure with radio galaxies
we have performed a small redshift survey, selecting 29 radio galaxies in the
range 0.19<z<0.45 from a contiguous 40 square degree area of sky. We detect
significant clustering within this sample. The amplitude of the two-point
correlation function we measure is consistent with no evolution from the local
(z<0.1) value. This is as expected in a model in which radio galaxy hosts form
at high redshift and thereafter obey a continuity equation, although the
signal:noise of the detection is too low to rule out other models. Larger
surveys out to z~1 should reveal the structures of superclusters at
intermediate redshifts and strongly constrain models for the evolution of
large-scale structure.Comment: 7 pages, 3 figures, accepted by ApJ Letter
HST and UKIRT imaging observations of z ~ 1 6C radio galaxies - I. The data
The results of Hubble Space Telescope and UKIRT imaging observations are
presented for a sample of 11 6C radio galaxies with redshifts 0.85 < z < 1.5.
The observations of the 6C sources reveal a variety of different features,
similar to those observed around the higher luminosity of the aligned emission
appears less extreme in the case of the 6C radio galaxies. For both samples,
the aligned emission clearly cannot be explained by a single emission
mechanism; line emission and related nebular continuum emission, however, often
provide a significant contribution to the aligned emission.Comment: 17 pages, 11 figures (figs 3,6,11 low resolution - full resolution
images can be obtained from http://www.mrao.cam.ac.uk/~kji/ImagingFigs/).
Accepted for publication in MNRA
A submillimetre survey of the star-formation history of radio galaxies
We present the results of the first major systematic submillimetre survey of
radio galaxies spanning the redshift range 1 < z < 5. The primary aim of this
work is to elucidate the star-formation history of this sub-class of elliptical
galaxies by tracing the cosmological evolution of dust mass. Using SCUBA on the
JCMT we have obtained 850-micron photometry of 47 radio galaxies to a
consistent rms depth of 1 mJy, and have detected dust emission in 14 cases. The
radio galaxy targets have been selected from a series of low-frequency radio
surveys of increasing depth (3CRR, 6CE, etc), in order to allow us to separate
the effects of increasing redshift and increasing radio power on submillimetre
luminosity. Although the dynamic range of our study is inevitably small, we
find clear evidence that the typical submillimetre luminosity (and hence dust
mass) of a powerful radio galaxy is a strongly increasing function of redshift;
the detection rate rises from 15 per cent at z 2.5,
and the average submillimetre luminosity rises as (1+z)^3 out to z~4. Moreover
our extensive sample allows us to argue that this behaviour is not driven by
underlying correlations with other radio galaxy properties such as radio power,
radio spectral index, or radio source size/age. Although radio selection may
introduce other more subtle biases, the redshift distribution of our detected
objects is in fact consistent with the most recent estimates of the redshift
distribution of comparably bright submillimetre sources discovered in blank
field surveys. The evolution of submillimetre luminosity found here for radio
galaxies may thus be representative of massive ellipticals in general.Comment: 31 pages - 10 figures in main text, 3 pages of figures in appendix.
This revised version has been re-structured, but the analysis and conclusions
have not changed. Accepted for publication in MNRA
High spatial resolution observations of CUDSS14A: a SCUBA-selected ultraluminous galaxy at high redshift
The definitive version is available at www.blackwell-synergy.com '. Copyright Blackwell Publishing DOI : 10.1046/j.1365-8711.2000.03822.xWe present a high-resolutionmillimetre interferometric image of the brightest SCUBA- selected galaxy from the Canada-UK deep SCUBA survey (CUDSS). We make a very clear detection at 1.3 mm, but fail to resolve any structure in the source.Peer reviewe
The Subillimeter Properties of Extremely Red Objects in the CUDSS Fields
We discuss the submillimeter properties of Extremely Red Objects (EROs) in
the two Canada-UK Deep Submillimeter Survey (CUDSS) Fields. We measure the mean
submillimeter flux of the ERO population (to K < 20.7) and find 0.4 +/- 0.07
mJy for EROs selected by (I-K) > 4.0 and 0.56 +/- 0.09 mJy for EROs selected by
(R-K) > 5.3 but, these measurements are dominated by discrete, bright
submillimeter sources. We estimate that EROs produce 7-11% of the far-infrared
background at 850um. This is substantially less than a previous measurement by
Wehner, Barger & Kneib (2002) and we discuss possible reasons for this
discrepancy. We show that ERO counterparts to bright submillimeter sources lie
within the starburst region of the near-infrared color-color plot of Pozzetti &
Mannucci (2000). Finally, we claim that pairs or small groups of EROs with
separations of < 10 arcseconds often mark regions of strong submillimeter flux.Comment: 9 pages, 8 figures, accepted for publication in Ap
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