953 research outputs found
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
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
Smoking Supernovae
The question "Are supernovae important sources of dust?" is a contentious one. Observations with the Infrared Astronomical Satellite (IRAS) and the Infrared Space Observatory (ISO) only detected very small amounts of hot dust in supernova remnants. Here, we review observations of two young Galactic remnants with the Submillimetre Common User Bolometer Array (SCUBA), which imply that large quantities of dust are produced by supernovae. The association of dust with the Cassiopeia A remnant is in question due to the contamination of foreground material. In this article, we compare the emission from cold dust with CO emission towards Kepler's supernova remnant. We detect very little CO at the location of the submillimetre peaks. A comparison of masses from the CO and the dust clouds are made, and we estimate the 3 sigma upper limit on the gas-to-dust ratios to range from 25 - 65 suggesting that we cannot yet rule out freshly-formed or swept up circumstellar dust in Kepler's supernova remnant
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
CENSORS: A Combined EIS-NVSS Survey Of Radio Sources. I. Sample definition, radio data and optical identifications
A new sample of radio sources, with the designated name CENSORS (A Combined
EIS-NVSS Survey Of Radio Sources), has been defined by combining the NRAO VLA
Sky Survey (NVSS) at 1.4 GHz with the ESO Imaging Survey (EIS) Patch D, a 3 by
2 degree region of sky centred at 09 51 36.0, -21 00 00 (J2000). New radio
observations of 199 NVSS radio sources with NVSS flux densities S(1.4GHz) >
7.8mJy are presented, and compared with the EIS I-band imaging observations
which reach a depth of I~23; optical identifications are obtained for over
two-thirds of the ~150 confirmed radio sources within the EIS field. The radio
sources have a median linear size of 6 arcseconds, consistent with the trend
for lower flux density radio sources to be less extended. Other radio source
properties, such as the lobe flux density ratios, are consistent with those of
brighter radio source samples. From the optical information, 30-40% of the
sources are expected to lie at redshifts z >~ 1.5.
One of the key goals of this survey is to accurately determine the high
redshift evolution of the radio luminosity function. These radio sources are at
the ideal flux density level to achieve this goal; at redshifts z~2 they have
luminosities which are around the break of the luminosity function and so
provide a much more accurate census of the radio source population at those
redshifts than the existing studies of extreme, high radio power sources. Other
survey goals include investigating the dual--population unification schemes for
radio sources, studying the radio luminosity dependence of the evolution of
radio source environments, and understanding the radio power dependence of the
K-z relation for radio galaxies.Comment: Accepted for publication in MNRAS. 28 pages plus 36 reduced
resolution jpeg figures. A postscript version with full resolution figures
included in the text is available from
http://www.roe.ac.uk/~pnb/censors.ps.g
FIR/submm spectroscopy with Herschel: first results from the VNGS and H-ATLAS surveys
The FIR/submm window is one of the least-studied regions of the
electromagnetic spectrum, yet this wavelength range is absolutely crucial for
understanding the physical processes and properties of the ISM in galaxies. The
advent of the Herschel Space Observatory has opened up the entire FIR/submm
window for spectroscopic studies. We present the first FIR/submm spectroscopic
results on both nearby and distant galaxies obtained in the frame of two
Herschel key programs: the Very Nearby Galaxies Survey and the Herschel ATLAS
A Radio Galaxy at z=5.19
We report the discovery of the most distant known AGN, the radio galaxy TN
J0924-2201 at z = 5.19. The radio source was selected from a new sample of
ultra-steep spectrum (USS) sources, has an extreme radio spectral index
alpha_365MHz^1.4GHz = -1.63, and is identified at near-IR wavelengths with a
very faint, K = 21.3 +- 0.3 object. Spectroscopic observations show a single
emission line at lambda ~ 7530A, which we identify as Ly-alpha. The K-band
image, sampling rest frame U-band, shows a multi-component, radio-aligned
morphology, typical of lower-redshift radio galaxies. TN J0924-2201 extends the
near-IR Hubble, or K-z, relation for powerful radio galaxies to z > 5, and is
consistent with models of massive galaxies forming at even higher redshifts.Comment: 11 Pages, including 3 PostScript figures. Accepted for publication in
the Astrophysical Journal Letter
Deep Galaxy survey at 6.75 micron with the ISO satellite
Deep 6.75um mid-IR ISOCAM observations were obtained of the Canada-France
Redshift Survey (CFRS) 1415+52 field with the Infrared Space Observatory. The
identification of the sources with optical counterparts is described in detail,
and a classification scheme is devised which depends on the S/N of the
detection and the inverse probability of chance coincidence. 83% of the 54
ISOCAM sources are identified with Iab<23.5 counterparts. The (I-K)ab colors,
radio properties, spectrophotometric properties and frequency of nuclear
activity of these counterparts differ on average from those of typical CFRS
galaxies. CFRS spectra are available for 21 of the sources which have Iab <=
22.5 (including 7 stars). Most of the strongest sources are stars or AGN. Among
the non--stellar counterparts with spectra, 40% are AGNs, and 53% are galaxies
that display star formation activity and/or significant contributions of A
stars. The ISOCAM sources also display an IR excess, even when compared with
heavily-reddened local starburst galaxies. An upper limit of 30% of
extragalactic ISO sources could be at z>1 of the 44 S6.75um > 150uJy sources
which are non-stellar (7 "spectroscopic" and 3 "photometric" stars excluded)Comment: 13 pages, 12 figures. Accepted for publication in A
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