304 research outputs found
A robust method for investigating galactic evolution in the submillimetre waveband: II the submillimetre background and source counts
This is the second of two papers describing a model of galactic evolution in
the submillimetre waveband. The model incorporates a self-consistent treatment
of the evolution of dust and stars, is normalized to the submillimetre
properties of galaxies in the local universe, and can be used to make
predictions for both disk and elliptical galaxies and for `closed-box',
`inflow', and `outflow' models of galactic evolution. In Paper I we
investigated whether it is possible to explain the extreme dust masses of
high-redshift quasars and radio galaxies by galactic evolution. In this paper
we use the model to make predictions of the submillimetre background and source
counts. All our disk-galaxy models exceed at short wavelengths the
submillimetre background recently measured by Puget et al. (1996). We also find
that it is possible to fit the background over the entire wavelength range with
a elliptical model but not with a disk model. We make source count predictions
at 190 m for the ISOPHOT instrument on ISO and at 850 m for SCUBA. We
show that the shape of the 850 m source counts depends almost entirely on
the mass spectrum of the radiating objects. Finally, we consider the
limitations of the models. We find that one of the biggest uncertainties in the
model is our lack of information about the submillimetre properties of nearby
galaxies, in particular the lack of a direct measurement of the submillimetre
luminosity function.Comment: 17 pages, 9 postscript figures, TEX, accepted by MNRA
Non-steller light from high-redshift radiogalaxies
With the aid of a new IRCAM image of 3C356, researchers question the common assumption that radiosource-stimulated starbursts are responsible for the extended optical emission aligned with radio structures in high-redshift radiogalaxies. They propose an alternative model in which the radiation from a hidden luminous quasar is beamed along the radio axis and illuminates dense clumps of cool gas to produce both extended narrow emission line regions and, by Thomson scattering, extended optical continua. Simple observational tests of this model are possible and necessary if we are to continue to accept that the color, magnitude and shape evolution of radiogalaxies are controlled by the active evolution of stellar populations
Morphology and Surface Brightness Evolution of z\sim1.1 Radio Galaxies
We use 1\leq z\leq 1.4z\sim 1.1z<0.2z\sim 1.1L\sim L^*\sim 25\sim 1000$ lower in radio
luminosity. Hence the 6C radio galaxies may undergo at least as much optical
and radio evolution as the 3CR galaxies.Comment: 17 pages, 7 postscript figures, TEX, submitted to MNRA
The Clustering of K\sim 20 Galaxies on 17 Radio Galaxy Fields
We investigate the angular correlation function, , of the
galaxi es detected in the K-band on 17 fields (101.5 square arcmin in total),
each containing a radio galaxy. There is a significant detection of
galaxy clustering at limits, with an amplitude higher than expected
from simple models which fit the faint galaxy clustering in the blue and red
passbands, but consistent with a pure luminosity evolution model i f clustering
is stable and early-type galaxies have a steeper correlation function than
spirals. We do not detect a significant cross-correlation between the radio
galaxies and the other galaxies on these fields, obtaining upper limits
consistent with a mean clustering environment of Abell class 0 for
radio galaxies, similar to that observed for radio galaxies at . At
, the number of galaxy-galaxy pairs of 2--3 arcsec separations
exceeds the random expectation by a factor of . This excess
suggests at least a tripling of the local merger rate at .Comment: 13 pages, 3 tables, 7 postscript figures, TEX, submitted to MNRA
The SCUBA Local Universe Galaxy Survey Optically-Selected Sample
We discuss the progress of the SCUBA Local Universe Galaxy Survey (SLUGS),
the first large, statistical sub-mm survey of the local universe. Since our
original survey of a sample of 104 IRAS-selected galaxies we have recently
completed a sample of 78 Optically-Selected galaxies. Since SCUBA is sensitive
to the large proportion of dust too cold to be detected by IRAS the addition of
this optically-selected sample allows us for the first time to determine the
amount of cold dust in galaxies of different Hubble types. We detect 6
ellipticals in the sample and find them to have dust masses in excess of 10^7
solar masses. We derive local sub-mm luminosity functions, both directly for
the two samples, and by extrapolation from the IRAS PSCz, and find excellent
agreement.Comment: 2 pages, 2 figures. In the proceedings of the conference:
"Penetrating Bars through Masks of Cosmic Dust: The Hubble Tuning Fork
Strikes a New Note", South Africa, June 2004 (Kluwer
Evidence against a simple two-component model for the far-infrared emission from galaxies
Two of the first Infrared Astronomy Satellite (IRAS) results were that galaxies have a wide range of values for the ratio of 60 micron to 100 micron flux density (0.2 less than or equal to S sub 60/S sub 100 less than or equal to 1.0) and that this ratio is correlated with L sub fir, L sub b, L sub fir being the total far-infrared luminosity and L sub b being the luminosity at visible wavelengths (de Jong et al. 1984; Soifer et al. 1984). From these results arose the following simple model for the far-infrared emission from galaxies (de Jong et al. 1984), which has remained the standard model ever since. In this model, the far-infrared emission comes from two dust components: warm dust (T approx. equals 50 K) intermingled with, and heated by, young massive OB stars in molecular clouds and HII regions, and colder dust (T approx. equals 20 K) associated with the diffuse atomic hydrogen in the interstellar medium and heated by the general interstellar radiation field. As the number of young stars in a galaxy increases, S sub 60/S sub 100 increases, because there is a greater proportion of warm dust, and so does L sub fir/L sub b, because most of the radiation from the young stars is absorbed by the dust, leading to a swifter increase in far-infrared emission than in visible light. Although this model explains the basic IRAS results, it is inelegant. It uses two free parameters to fit two data (the 60 and 100 micron flux densities)-and there are now several observations that contradict it. Despite these major problems with the two-component model, it is not clear what should be put in its place. When considering possible models for the far-infrared emission from galaxies, the observational evidence for our own galaxy must be considered. Researchers suspect that the study by Boulanger and Perault (1988) of the far-infrared properties of the local interstellar medium may be particularly relevant. They showed that molecular clouds are leaky - that most of the light from OB stars in molecular clouds does not heat the dust in the clouds, but instead leaks out. The consequence of this is that that while most of the far-infrared emission from the solar neighborhood is from dust associated with diffuse HI, this dust is mostly heated by young stars
The SCUBA Local Universe Galaxy Survey: Results from the Optically-Selected Sample
We present new results from the SCUBA Local Universe Galaxy Survey, the first
large statistical submillimetre survey of the local Universe. Following our
initial survey of a sample of 104 IRAS-selected galaxies we now present the
results of a sample of 80 Optically-selected galaxies. Since SCUBA is sensitive
to the large proportion of dust too cold to be detected by IRAS the addition of
this Optically-selected sample allows us for the first time to determine the
amount of cold dust in galaxies of different Hubble types. We detect 6
ellipticals in the sample and find them to have dust masses in excess of 10^7
solar masses. We derive local submillimetre Luminosity Functions and Dust Mass
functions, both directly for the Optically-Selected SLUGS sample and by
extrapolation from the IRAS PSCz survey, and find them to be well-fitted by
Schechter functions. We find excellent agreement between the two LFs and DMFs
and show that, whereas the slope of the IRAS-selected LF at lower luminosities
was steeper than -2 (a submm "Olbers' Paradox"), as expected the
PSCz-extrapolated LF flattens out at the low luminosity end.Comment: 2 pages, 4 figures. To be published in proceedings of the conference:
"The Dusty and Molecular Universe - A Prelude to HERSCHEL and ALMA", Paris,
October 2004 (ESA Publications
Faint radio samples: the key to understanding radio galaxies
The large number of differences between high- and low-redshift radio galaxies
have almost all been discovered by looking at the bright 3C sample of radio
sources. This has the disadvantage that the strong correlation between radio
luminosity and redshift within a single sample makes it impossible to be
determine whether these differences are the result of cosmic evolution or
whether they are simply the result of source properties depending on radio
luminosity. The solution to this problem is to compare the properties of
sources in faint samples with those of the 3C sources. I and collaborators have
recently removed the degeneracy between redshift and radio luminosity by
comparing the 3C sample to the recently completed 6C and 7C samples. In this
paper I concentrate on what our study has revealed about the host galaxies of
radio sources. At low redshift, radio galaxies are giant ellipticals with
absolute magnitude being independent of radio luminosity over a range of in radio luminosity. At , the radio-luminous 3C radio galaxies
are still giant ellipticals, but the 6C galaxies, only a factor of six lower in
radio luminosity, are fainter by about 1 mag in the near-IR and have much more
compact near-IR structures. At , radio galaxies follow a line in a
diagram of optical luminosity verses de Vaucouleurs scale length parallel to
the projection of the fundamental plane for nearby ellipticals in this diagram.
I discuss the significance of these results for our understanding of radio
galaxies.Comment: to be published in `The most distant radio galaxies' KNAW Colloquium,
Amsterdam, October 1997, eds Best et al., Kluwer. 15 pages of LaTex, 4
postscript figures, uses knawproc.cl
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
- …