This is the first of a series of papers presenting results from the SCUBA Local Universe Galaxy Survey (SLUGS), the first statistical survey of the submillimetre properties of the local Universe. As the initial part of this survey, we have used the SCUBA camera on the James Clerk Maxwell Telescope to observe 104 galaxies from the IRAS Bright Galaxy Sample. We present here the 850‐μm flux measurements. The 60‐, 100‐, and 850‐μm flux densities are well fitted by single‐temperature dust spectral energy distributions, with the sample mean and standard deviation for the best‐fitting temperature being Td=35.6±4.9 K and for the dust emissivity index β=1.3±0.2. The dust temperature was found to correlate with 60‐μm luminosity. The low value of β may simply mean that these galaxies contain a significant amount of dust that is colder than these temperatures. We have estimated dust masses from the 850‐μm fluxes and from the fitted temperature, although if a colder component at around 20 K is present (assuming a β of 2), then the estimated dust masses are a factor of 1.5–3 too low. We have made the first direct measurements of the submillimetre luminosity function (LF) and of the dust mass function. Unlike the IRAS 60‐μm LF, these are well fitted by Schechter functions. The slope of the 850‐μm LF at low luminosities is steeper than −2, implying that the LF must flatten at luminosities lower than we probe here. We show that extrapolating the 60‐μm LF to 850 μm using a single temperature and β does not reproduce the measured submillimetre LF. A population of ‘cold’ galaxies (Td<25 K) emitting strongly at submillimetre wavelengths would have been excluded from the 60‐μm‐selected sample. If such galaxies do exist, then this estimate of the 850‐μm flux is biased (it is underestimated). Whether such a population does exist is unknown at present. We correlate many of the global galaxy properties with the FIR/submillimetre properties. We find that there is a tendency for less luminous galaxies to contain hotter dust and to have a greater star formation efficiency (cf. Young). The average gas‐to‐dust ratio for the sample is 581±43 (using both the atomic and molecular hydrogen), which is significantly higher than the Galactic value of 160. We believe that this discrepancy is probably due to a ‘cold dust’ component at Td≤20 K in our galaxies. There is a surprisingly tight correlation between dust mass and the mass of molecular hydrogen, estimated from CO measurements, with an intrinsic scatter of ≃50 per cent.

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We analyze the behavior of N/O and C/O abundance ratios as a function of metallicity as gauged by O/H in large, extant Galactic and extragalactic H II region abundance samples. We compile and compare published yields of C, N, and O for intermediate mass and massive stars and choose appropriate yield sets based upon analytical chemical evolution models fitted to the abundance data. We then use these yields to compute numerical chemical evolution models which satisfactorily reproduce the observed abundance trends and thereby identify the most likely production sites for carbon and nitrogen. Our results suggest that carbon and nitrogen originate from separate production sites and are decoupled from one another. Massive stars (M>8 M ⊙ ) dominate the production of carbon, while intermediate-mass stars between 4 and 8 M ⊙ , with a characteristic lag time of roughly 250 Myr following their formation, dominate nitrogen production. Carbon production is positively sensitive to metallicity through mass loss processes in massive stars and has a pseudo-secondary character. Nitrogen production in intermediate mass stars is primary at low metallicity, but when 12+log(O/H)>8.3, secondary nitrogen becomes prominent, and nitrogen increases at a faster rate than oxygen -indeed the dependence is steeper than would be formally expected for a secondary element. The observed flat behavior of N/O versus O/H in metal-poor galaxies is explained by invoking low star formation rates which flatten the age-metallicity relation and allow N/O to rise

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Large amounts of dust (> 10 8 M ⊙ ) have recently been discovered in high redshifts quasars 1,2 and galaxies 3−5 , corresponding to a time when the Universe was less than one-tenth of its present age. The stellar winds produced by stars in the late stages of their evolution (on the asymptotic giant branch of the Hertzsprung-Russell diagram) are though to be the main source of dust in galaxies, but they cannot produce that dust on a short-enough timescale 6 (< 1 Gyr) to explain the results in the high-redshift galaxies.Supernova explosions of massive stars (type II) are also a potential source, with models predicting 0.2-4 M ⊙ of dust 7−10 . As massive stars evolve rapidly, on timescales of a few Myr, these supernovae could be responsible for the high-redshift dust. Observations 11−13 of supernova remnants in the Milky Way, however, have hitherto revealed only 10 −7 − 10 −3 M ⊙ of dust each, which is insufficient to explain the high-redshift data. Here we report the detection of ∼ 2 − 4 M ⊙ of cold dust in the youngest known Galactic remnant, Cassiopeia A. This observation implies that supernovae are at least as important as stellar winds in producing dust in our Galaxy and would have been the dominant source of dust at high redshifts.Over the past three decades, many searches for dust in supernova remnants (SNR) have been made in the mid and far-infrared (6-100µm). Remnants must be studied when they are young, before they have swept up large masses of interstellar material which makes it difficult to distinguish dust formed in the ejecta from that present in the ISM prior to the explosion. The handful of Galactic remnants which are both young and close enough (Cas A, Kepler and Tycho) have been studied with the Infrared Astronomical Satellite (IRAS) and the Infrared Space Observatory (ISO), but although dust at 100-200 K has been detected, the dust mass deduced is only 10 −7 − 10 −3 M ⊙ , many orders of magnitude lower than the solar mass quantities predicted. 11−13 The formation of dust in the recent supernova 1987A has been implied indirectly from the fading of the silicate line and increase in 10µm emission, 14 although the quantity is heavily dependant on the assumptions made 1

Using a new technique, we have determined a value for the constant of proportionality between submillimetre emission and dust mass, the dust mass–absorption coefficient (κd) at 850μm. Our method has an advantage over previous methods in that we avoid assumptions about the properties of dust in the interstellar medium. Our only assumption is that the fraction of metals incorporated in the dust (ɛ) in galaxies is a universal constant. To implement our method, we require objects that have submillimetre and far‐infrared flux measurements as well as gas mass and metallicity estimates. We present data for all the galaxies with suitable measurements, including new submillimetre maps for five galaxies. We find κ850= 0.07 ± 0.02 m2 kg−1. We have also been able to use our sample to investigate our assumption that ɛ is a universal constant. We find no evidence that ɛ is different for dwarf and giant galaxies, and show that the scatter in ɛ from galaxy to galaxy is apparently quite small.

We investigate the sources and amount of dust in early galaxies. We discuss dust nucleation in stellar atmospheres using published extended atmosphere models, stellar evolution tracks and nucleation conditions. The thermally pulsating asymptotic giant branch phase of intermediate‐mass stars is likely to be the most promising site for dust formation in stellar winds. We present an elementary model including dust formation time‐scales in which the amount of dust in the interstellar medium is governed by chemical evolution. The implications of the model for high‐redshift galaxies are investigated and we show there is no difficulty in producing dusty galaxies at redshifts above 5 if supernovae are a dominant source of interstellar dust. If dust does not condense efficiently in supernovae then significant dust masses can only be generated at z > 5 by galaxies with a high star formation efficiency. This is consistent with the high star formation rates implied by submillimetre sources found in deep Submillimetre Common User Bolometric Array surveys. We find the visual optical depth for individual star‐forming clouds can reach values greater than 1 at very low metallicity (1/100 solar) provided that the mass–radius exponent of molecular clouds is less than 2. Most of the radiation from star formation will emerge at infrared wavelengths in the early Universe provided that dust is present. The (patchy) visual optical depth through a typical early galaxy will, however, remain less than 1 on average until a metallicity of 1/10 solar is reached.

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