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 $\mu$m for the ISOPHOT instrument on ISO and at 850 $\mu$m for SCUBA. We show that the shape of the 850 $\mu$ 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

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

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

The Clustering of K\sim 20 Galaxies on 17 Radio Galaxy Fields

We investigate the angular correlation function, $\omega(\theta)$, of the galaxi es detected in the K-band on 17 fields (101.5 square arcmin in total), each containing a $z\sim 1.1$ radio galaxy. There is a significant detection of galaxy clustering at $K\sim 20$ 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 $z\sim 1.1$ radio galaxies, similar to that observed for radio galaxies at $z\sim 0.5$. At $K\leq 20$, the number of galaxy-galaxy pairs of 2--3 arcsec separations exceeds the random expectation by a factor of $2.15\pm 0.26$. This excess suggests at least a tripling of the local merger rate at $z\sim 1$.Comment: 13 pages, 3 tables, 7 postscript figures, TEX, submitted to MNRA

The Canada-UK Deep Sub-Millimeter Survey II: First identifications, redshifts and implications for galaxy evolution

Identifications are sought for 12 sub-mm sources detected by Eales et al (1998). Six are securely identified, two have probable identifications and four remain unidentified with I_AB > 25. Spectroscopic and estimated photometric redshifts indicate that four of the sources have z < 1, and four have 1 < z < 3, with the remaining four empty field sources probably lying at z > 3. The spectral energy distributions of the identifications are consistent with those of high extinction starbursts such as Arp 220. The far-IR luminosities of the sources at z > 0.5 are of order 3 x 10^12 h_50^-2 L_sun, i.e. slightly larger than that of Arp 220. Based on this small sample, the cumulative bolometric luminosity function shows strong evolution to z ~ 1, but weaker or possibly even negative evolution beyond. The redshift dependence of the far-IR luminosity density does not appear, at this early stage, to be inconsistent with that seen in the ultraviolet luminosity density. Assuming that the energy source in the far-IR is massive stars, the total luminous output from star-formation in the Universe is probably dominated by the far-IR emission. The detected systems have individual star-formation rates (exceeding 300 h_50^-2 M_O yr^-1) that are much higher than seen in the ultraviolet selected samples, and which are sufficient to form substantial stellar populations on dynamical timescales of 10^8 yr. The association with merger-like morphologies and the obvious presence of dust makes it attractive to identify these systems as forming the metal-rich spheroid population, in which case we would infer that much of this activity has occurred relatively recently, at z ~ 2.Comment: 17 pages text + 14 figures. Accepted for publication in the Astrophysical Journal. Gzipped tar file contains one text.ps file for text and tables, one Fig2.jpg file for Fig 2, and 13 Fig*.ps files for the remaining figure

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

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 $\rm 10^4$ in radio luminosity. At $z \sim 1$, 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 $z \sim 1$, 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