We report far-infrared and submillimeter observations of supernova 1987A, the star whose explosion was observed on 23 February 1987 in the Large Magellanic Cloud, a galaxy located 160,000 light years away. The observations reveal the presence of a population of cold dust grains radiating with a temperature of about 17 to 23 kelvin at a rate of about 220 times the luminosity of the Sun. The intensity and spectral energy distribution of the emission suggest a dust mass of about 0.4 to 0.7 times the mass of the Sun. The radiation must originate from the supernova ejecta and requires the efficient precipitation of all refractory material into dust. Our observations imply that supernovae can produce the large dust masses detected in young galaxies at very high redshifts.

Abstract. We present an empirical determination of the mass-loss rate as a function of stellar luminosity and effective temperature, for oxygen-rich dust-enshrouded Asymptotic Giant Branch stars and red supergiants. To this aim we obtained optical spectra of a sample of dust-enshrouded red giants in the Large Magellanic Cloud, which we complemented with spectroscopic and infrared photometric data from the literature. Two of these turned out to be hot emission-line stars, of which one is a definite B[e] star. The mass-loss rates were measured through modelling of the spectral energy distributions. We thus obtain the massloss rate formula logṀ = −5.65 + 1.05 log(L/10 000 L ) − 6.3 log(T eff /3500 K), valid for dust-enshrouded red supergiants and oxygen-rich AGB stars. Despite the low metallicity of the LMC, both AGB stars and red supergiants are found at late spectral types. A comparison with galactic AGB stars and red supergiants shows excellent agreement between the mass-loss rate as predicted by our formula and that derived from the 60 µm flux density for dust-enshrouded objects, but not for optically bright objects. We discuss the possible implications of this for the mass-loss mechanism.

We compare atomic gas, molecular gas, and the recent star formation rate (SFR) inferred from Hα in the Small Magellanic Cloud (SMC). By using infrared dust emission and local dust-to-gas ratios, we construct a map of molecular gas that is independent of CO emission. This allows us to disentangle conversion factor effects from the impact of metallicity on the formation and star formation efficiency of molecular gas. On scales of 200 pc to 1 kpc (where the distributions of H 2 and star formation match well) we find a characteristic molecular gas depletion time of τ mol dep ∼ 1.6 Gyr, similar to that observed in the molecule-rich parts of large spiral galaxies on similar spatial scales. This depletion time shortens on much larger scales to ∼0.6 Gyr because of the presence of a diffuse Hα component, and lengthens on much smaller scales to ∼7.5 Gyr because the Hα and H 2 distributions differ in detail. We estimate the systematic uncertainties in our dust-based τ mol dep measurement to be a factor of ∼2-3. We suggest that the impact of metallicity on the physics of star formation in molecular gas has at most this magnitude, rather than the factor of ∼40 suggested by the ratio of SFR to CO emission. The relation between SFR and neutral (H 2 + H i) gas surface density is steep, with a power-law index ≈2.2 ± 0.1, similar to that observed in the outer disks of large spiral galaxies. At a fixed total gas surface density the SMC has a 5-10 times lower molecular gas fraction (and star formation rate) than large spiral galaxies. We explore the ability of the recent models by Krumholz et al. and Ostriker et al. to reproduce our observations. We find that to explain our data at all spatial scales requires a low fraction of cold, gravitationally bound gas in the SMC. We explore a combined model that incorporates both large-scale thermal and dynamical equilibrium and cloud-scale photodissociation region structure and find that it reproduces our data well, as well as predicting a fraction of cold atomic gas very similar to that observed in the SMC.

We present the initial results from the Spitzer Survey of the Small Magellanic Cloud (S 3 MC), which imaged the star-forming body of the Small Magellanic Cloud (SMC) in all seven MIPS and IRAC wavebands. We find that the F 8 /F 24 ratio (an estimate of PAH abundance) has large spatial variations and takes a wide range of values that are unrelated to metallicity but anticorrelated with 24 µm brightness and F 24 /F 70 ratio. This suggests that photodestruction is primarily responsible for the low abundance of PAHs observed in star-forming low-metallicity galaxies. We use the S 3 MC images to compile a photometric catalog of ∼ 400, 000 mid-and far-infrared point sources in the SMC. The sources detected at the longest wavelengths fall into four main categories: 1) bright 5.8 µm sources with very faint optical counterparts and very red mid-infrared colors ([5.8] − [8.0] > 1.2), which we identify as YSOs. 2) Bright mid-infrared sources with mildly red colors (0.16 [5.8] − [8.0] < 0.6), identified as carbon stars. 3) Bright mid-infrared sources with neutral colors and bright optical counterparts, corresponding to oxygen-rich evolved stars. And, 4) unreddened early B stars (B3 to O9) with a large 24 µm excess. This excess is reminiscent of debris disks, and is detected in only a small fraction of these stars ( 5%). The majority of the brightest infrared point sources in the SMC fall into groups one to three. We use this photometric information to produce a catalog of 282 bright YSOs in the SMC with a very low level of contamination (∼ 7%).

Context. The new VISual and Infrared Telescope for Astronomy (VISTA) has started operations. Over its first five years it will be collecting data for six public surveys, one of which is the near-infrared Y JK s VISTA survey of the Magellanic Clouds system (VMC). This survey comprises the Large Magellanic Cloud (LMC), the Small Magellanic Cloud, the Magellanic Bridge connecting the two galaxies and two fields in the Magellanic Stream. Aims. This paper provides an overview of the VMC survey strategy and presents first science results. The main goals of the VMC survey are the determination of the spatially-resolved star-formation history and the three-dimensional structure of the Magellanic system. The VMC survey is therefore designed to reach stars as faint as the oldest main sequence turn-off point and to constrain the mean magnitude of pulsating variables such as RR Lyrae stars and Cepheids. This paper focuses on observations of VMC fields in the LMC obtained between November 2009 and March 2010. These observations correspond to a completeness of 7% of the planned LMC fields. Methods. The VMC data are comprised of multi-epoch observations which are executed following specific time constraints. The data were reduced using the VISTA Data Flow System pipeline with source catalogues, including astrometric and photometric corrections, produced and made available via the VISTA Science Archive. The VMC data will be released to the astronomical community following the European Southern Observatory's Public Survey policy. The analysis of the data shows that the sensitivity in each wave band agrees with expectations. Uncertainties and completeness of the data are also derived. Results. The first science results, aimed at assessing the scientific quality of the VMC data, include an overview of the distribution of stars in colour-magnitude and colour-colour diagrams, the detection of planetary nebulae and stellar clusters, and the K s band light-curves of variable stars. Conclusions. The VMC survey represents a tremendous improvement, in spatial resolution and sensitivity, on previous panoramic observations of the Magellanic system in the near-infrared, providing a powerful complement to deep observations at other wavelengths.