A. Dapergolas

The European Large Area ISO Survey - I. Goals, definition and observations

We describe the European Large Area ISO Survey (ELAIS). ELAIS was the largest single Open Time project conducted by ISO, mapping an area of 12deg^2 at 15μm with ISOCAM and at 90μm with ISOPHOT. Secondary surveys in other ISO bands were undertaken by the ELAIS team within the fields of the primary survey, with 6deg^2 being covered at 6.7μm and 1deg^2 at 175μm. This paper discusses the goals of the project and the techniques employed in its construction, as well as presenting details of the observations carried out, the data from which are now in the public domain. We outline the ELAIS `preliminary analysis which led to the detection of over 1000 sources from the 15 and 90-μm surveys (the majority selected at 15μm with a flux limit of ~3mJy), to be fed into a ground-based follow-up campaign, as well as a programme of photometric observations of detected sources using both ISOCAM and ISOPHOT. We detail how the ELAIS survey complements other ISO surveys in terms of depth and areal coverage, and show that the extensive multi-wavelength coverage of the ELAIS fields resulting from our concerted and on-going follow-up programme has made these regions amongst the best studied areas of their size in the entire sky, and, therefore, natural targets for future surveys. This paper accompanies the release of extremely reliable subsets of the `preliminary analysis products. Subsequent papers in this series will give further details of our data reduction techniques, reliability and completeness estimates and present the 15- and 90-μm number counts from the `preliminary analysis, while a further series of papers will discuss in detail the results from the ELAIS `final analysis, as well as from the follow-up programme.

The European Large-Area ISO Survey (ELAIS): the final band-merged catalogue

We present the final band-merged European Large-Area ISO Survey (ELAIS) Catalogue at 6.7, 15, 90 and 175 mum, and the associated data at U, g, r, i, Z, J, H, K and 20 cm. The origin of the survey, infrared and radio observations, data-reduction and optical identifications are briefly reviewed, and a summary of the area covered and the completeness limit for each infrared band is given. A detailed discussion of the band-merging and optical association strategy is given. The total Catalogue consists of 3762 sources. 23 per cent of the 15-mum sources and 75 per cent of the 6.7-mum sources are stars. For extragalactic sources observed in three or more infrared bands, colour-colour diagrams are presented and discussed in terms of the contributing infrared populations. Spectral energy distributions (SEDs) are shown for selected sources and compared with cirrus, M82 and Arp220 starburst, and active galactic nuclei (AGN) dust torus models. Spectroscopic redshifts are tabulated, where available. For the N1 and N2 areas, the Isaac Newton Telescope ugriz Wide Field Survey permits photometric redshifts to be estimated for galaxies and quasars. These agree well with the spectroscopic redshifts, within the uncertainty of the photometric method [similar to10 per cent in (1 + z) for galaxies]. The redshift distribution is given for selected ELAIS bands and colour-redshift diagrams are discussed. There is a high proportion of ultraluminous infrared galaxies (log(10) of 1-1000 mum luminosity L-ir > 12.22) in the ELAIS Catalogue (14 per cent of 15-mum galaxies with known z), many with Arp220-like SEDs. 10 per cent of the 15-mum sources are genuine optically blank fields to r = 24: these must have very high infrared-to-optical ratios and probably have z > 0.6, so are high-luminosity dusty starbursts or Type 2 AGN. Nine hyperluminous infrared galaxies (L-ir > 13.22) and nine extremely red objects (EROs) (r - K > 6) are found in the survey. The latter are interpreted as ultraluminous dusty infrared galaxies at z similar to 1. The large numbers of ultraluminous galaxies imply very strong evolution in the star formation rate between z = 0 and 1. There is also a surprisingly large population of luminous (L-ir > 11.5), cool (cirrus-type SEDs) galaxies, with L-ir L-opt > 0, implying A(V) > 1.

The Gaia astrophysical parameters inference system (Apsis) - Pre-launch description

The Gaia satellite will survey the entire celestial sphere down to 20th magnitude, obtaining astrometry, photometry, and low resolution spectrophotometry on one billion astronomical sources, plus radial velocities for over one hundred million stars. Its main objective is to take a census of the stellar content of our Galaxy, with the goal of revealing its formation and evolution. Gaias unique feature is the measurement of parallaxes and proper motions with hitherto unparalleled accuracy for many objects. As a survey, the physical properties of most of these objects are unknown. Here we describe the data analysis system put together by the Gaia consortium to classify these objects and to infer their astrophysical properties using the satellites data. This system covers single stars, (unresolved) binary stars, quasars, and galaxies, all covering a wide parameter space. Multiple methods are used for many types of stars, producing multiple results for the end user according to different models and assumptions. Prior to its application to real Gaia data the accuracy of these methods cannot be assessed definitively. But as an example of the current performance, we can attain internal accuracies (RMS residuals) on F,G,K,M dwarfs and giants at G=15 (V=15-17) for a wide range of metallicites and interstellar extinctions of around 100K in effective temperature (Teff), 0.1mag in extinction (A0), 0.2dex in metallicity ([Fe/H]), and 0.25dex in surface gravity (logg). The accuracy is a strong function of the parameters themselves, varying by a factor of more than two up or down over this parameter range. After its launch in November 2013, Gaia will nominally observe for five years, during which the system we describe will continue to evolve in light of experience with the real data.

A Catalogue of carbon stars in the LMC

A catalogue of 7760 carbon stars in the Large Magellenic Cloud is presented. The stars were identified during a systematic survey of objective-prism plates taken with the UK 1.2 m Schmidt Telescope. The catalogue is compared with other lists of carbon stars and the distribution of the carbon stars is discussed.

Observations of the Hubble Deep Field South with the Infrared Space Observatory - II. Associations and star formation rates

We present results from a deep mid-infrared survey of the Hubble Deep Field South (HDF-S) region performed at 6.7 and 15mum with the ISOCAM instrument on board the Infrared Space Observatory (ISO ). We find reliable optical/near-infrared associations for 32 of the 35 sources detected in this field by Oliver et al. (Paper I): eight of them are identified as stars, one is definitely an active galactic nucleus (AGN), a second seems likely to be an AGN too, while the remaining 22 appear to be normal spiral or starburst galaxies. Using model spectral energy distributions (SEDs) of similar galaxies, we compare methods for estimating the star formation rates (SFRs) in these objects, finding that an estimator based on integrated (3-1000mum) infrared luminosity reproduces the model SFRs best. Applying this estimator to model fits to the SEDs of our 22 spiral and starburst galaxies, we find that they are forming stars at rates of ~1-100Msolar yr-1 , with a median value of ~40Msolar yr-1 , assuming an Einstein-de Sitter universe with a Hubble constant of 50kms-1 Mpc-1 , and star formation taking place according to a Salpeter initial mass function (IMF) across the mass range 0.1-100Msolar . We split the redshift range 0.0<=z <=0.6 into two equal-volume bins to compute raw estimates of the star formation rate density, rhod *, contributed by these sources, assuming the same cosmology and IMF as above and computing errors based on estimated uncertainties in the SFRs of individual galaxies. We compare these results with other estimates of rhod * made with the same assumptions, showing them to be consistent with the results of Flores et al. from their ISO survey of the CFRS 1415+52 field. However, the relatively small volume of our survey means that our rhod * estimates suffer from a large sampling variance, implying that our results, by themselves, do not place tight constraints on the global mean star formation rate density.

Observations of the Hubble Deep Field South with the Infrared Space Observatory - I. Observations, data reduction and mid-infrared source counts

We present results from a deep mid-infrared survey of the Hubble Deep Field South (HDF-S) region performed at 6.7 and 15 μm with the ISOCAM instrument on board the Infrared Space Observatory (ISO). The final map in each band was constructed by the co-addition of four independent rasters, registered using bright sources securely detected in all rasters, with the absolute astrometry being defined by a radio source detected at both 6.7 and 15 μm. We sought detections of bright sources in a circular region of radius 2.5 arcmin at the centre of each map, in a manner that simulations indicated would produce highly reliable and complete source catalogues using simple selection criteria. Merging source lists in the two bands yielded a catalogue of 35 distinct sources, which we calibrated photometrically using photospheric models of late-type stars detected in our data. We present extragalactic source count results in both bands, and discuss the constraints that they impose on models of galaxy evolution, given the volume of space sampled by this galaxy population.

The recent structural evolution of the SMC

We investigate the spatial distribution of stars of dierent ages towards the main body of the SMC, in an attempt to further understand the nature of the complex structure of the SMC. The old stellar population of the galaxy shows a rather regular and smooth distribution which is typical for a spheroidal body. On the contrary, the distribution of the younger stellar component is highly asymmetric and irregular giving evidence for the severe impact of the SMC during its close encounter with the LMC some 0.2 to 0.4 Gyr ago. In a series of isodensity contour maps of stars within selected ages, the recent structural evolution of the SMC is presented.

Towards a library of synthetic galaxy spectra and preliminary results of classification and parametrization of unresolved galaxies for Gaia. II

Aims. This paper is the second in a series, implementing a classification system for Gaia observations of unresolved galaxies. Our goals are to determine spectral classes and estimate intrinsic astrophysical parameters via synthetic templates. Here we describe (1) a new extended library of synthetic galaxy spectra; (2) its comparison with various observations; and (3) first results of classification and parametrization experiments using simulated Gaia spectrophotometry of this library. Methods. Using the PEGASE.2 code, based on galaxy evolution models that take account of metallicity evolution, extinction correction, and emission lines (with stellar spectra based on the BaSeL library), we improved our first library and extended it to cover the domain of most of the SDSS catalogue. Our classification and regression models were support vector machines (SVMs). Results. We produce an extended library of 28 885 synthetic galaxy spectra at zero redshift covering four general Hubble types of galaxies, over the wavelength range between 250 and 1050 nm at a sampling of 1 nm or less. The library is also produced for 4 random values of redshift in the range of 0–0.2. It is computed on a random grid of four key astrophysical parameters (infall timescale and 3 parameters defining the SFR) and, depending on the galaxy type, on two values of the age of the galaxy. The synthetic library was compared and found to be in good agreement with various observations. The first results from the SVM classifiers and parametrizers are promising, indicating that Hubble types can be reliably predicted and several parameters estimated with low bias and variance.

OB Stellar Associations in the Large Magellanic Cloud: Identification Method

We describe an objective method for the identification of stellar OB associations in the Large Magellanic Cloud under the assumption that they are loose, unbound stellar systems with a young OB stellar component. The method is based on star counts and spectral classification. First we detect the areas where an enhancement of star number density occurs above 3 σ of the average field density in large regions. The boundaries at 3 σ provide the size and morphology of the detected stellar concentrations. Further examination at different magnitude ranges allows us to select the systems with a bright stellar component within the detected areas. In the second step, star counts around the peak density of each detected stellar concentration provide a typical value of the projected half-mass radius, in order to calculate the central density using the appropriate mass function slope. The central density, being a crucial parameter for the bound and unbound systems, has been used as a tentative criterion for the distinction between open clusters and associations. Finally, spectral classification from objective-prism plates provides further evidence for the existence of OB-type stars in these concentrations. The faintest magnitude at which the various systems were detected is found to be independent of the presence or absence of gas and varies by up to 4 mag. An explanation for this effect is the possible existence of pre–main-sequence stars that are not visible in the optical region.

Star complexes and stellar populations in NGC 6822 - Comparison with the Magellanic Clouds

Aims. The star complexes (large scale star forming regions) of NGC 6822 were traced and mapped and their size distribution was compared with the size distribution of star complexes in the Magellanic Clouds (MCs). The spatial distributions of different age stellar populations were compared with each other. Methods. The star complexes of NGC 6822 were determined by using the isopleths, based on star counts, of the young stars of the galaxy, using a statistical cutoff limit in density. In order to map them and determine their geometric properties, an ellipse was fitted to each distinct region satisfying this minimum limit. The Kolmogorov-Smirnov statistical test was used to study possible patterns in their size distribution. Isopleths were also used to study the stellar populations of NGC 6822. Results. The star complexes of NGC 6822 were detected and a list of their positions and sizes was produced. Indications of hierarchical star formation, in terms of spatial distribution, time evolution and preferable sizes were found in NGC 6822 and the MCs. The spatial distribution of the various age stellar populations has indicated traces of an interaction in NGC 6822, dated before 350 ± 50 Myr.