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Register a new userThe European Large Area ISO Survey: ELAIS
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The European Large Area ISO Survey (ELAIS) has surveyed 12 square degrees of the sky at 15 and 90 microns, and subsets of this area at 6.75 and 175 microns, using the Infrared Space Observatory (ISO). This project was the largest single open time programme executed by ISO, taking 375 hours of data. A preliminary catalogue of more than 1000 galaxies has been produced. In this talk we describe the goals of the project, describe the follow-up programmes that are in progress, and present some first scientific results including a provisional number count analysis at 15 and 90 microns.
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We present the final band-merged ELAIS catalogue at 6.7, 15, 90, and 175 $mu$m, and the associated data at u,g,r,i,z,J,H,K, and 20cm. 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 completeness limit for each infrared band is given. A detailed discussion of the band-merging and optical association strategy is given. The total catalogues consists of 2860 sources. For extragalactic sources observed in 3 or more infrared bands, colour-colour diagrams are presented and discussed in terms of the contributing infrared populations. Spectral energy distributions are shown for selected sources and compared with cirrus, M82 and Arp220 starburst, and AGN dust torus models. Spectroscopic redshifts are tabulated, where available. For the N1 and N2 areas, the INT 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. The redshift distribution is given for selected ELAIS bands and colour-redshift diagrams are discussed. There is a high proportion of ultraluminous infrared galaxies in the ELAIS Catalogue ($> 10 %$ of 15 $mu$m sources), many with Arp220-like colours. 10 hyperluminous infrared galaxies and 10 EROs are found in the survey. The large numbers of ultraluminous galaxies imply very strong evolution in the star-formation rate between z = 0 and 1.
We present some recent results from the European Large Area ISO Survey (ELAIS). This survey was the largest non-serendipitous ISO field survey. A preliminary reduction has recently been completed and catalogues of sources released to the community. Early results show strongly evolving source counts. A comprehensive identification programme is underway and a number of extremely luminous objects have already been discovered. This survey provides an exciting legacy from the ISO mission and (amongst many goals) will allow us to provide important constraints on the obscured star-formation history of the Universe.
We describe the European Large Area ISO Survey (ELAIS). ELAIS was the largest single Open Time project conducted by ISO, mapping an area of 12 square degrees at 15mu with ISO-CAM and at 90mu with ISO-PHOT. Secondary surveys in other ISO bands were undertaken by the ELAIS team within the fields of the primary survey, with 6 square degrees being covered at 6.7mu and 1 square degree at 175mu. 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 mu surveys (the majority selected at 15mu with a flux limit of ~3 mJy), to be fed into a ground-based follow-up campaign, as well as a programme of photometric observations of detected sources using both ISO-CAM and ISO-PHOT. 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 sub-sets of the ``Preliminary Analysis products. Subsequent papers in this series will give further details of our data reduction techniques, reliability & completeness estimates and present the 15 and 90 nu 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) will provide Infrared observations of 4 regions in the sky with ISO. Around 2000 Infrared sources have been detected at 7 and 15 microns (with ISOCAM), 90 and 175 microns (with ISOPHOT)) over 13 square degrees of the sky. We present the source extraction pipeline of the 90 microns ISOPHOT observations, describe and discuss the results obtained and derive the limits of the ELAIS observational strategy.
We present the optical identification of mid-IR and radio sources detected in the European Large Area ISO Survey (ELAIS) areas N1 and N2. Using the r band optical data from the Wide Field Survey we apply a likelihood ratio method to search for the counterparts of the 1056 and 691 sources detected at 15 micron and 1.4 GHz respectively, down to flux limits of S_{15}=0.5 mJy and S_{1.4 GHz}=0.135 mJy. We find that ~92% of the 15 micron ELAIS sources have an optical counterpart down to the magnitude limit of the optical data, r=24. All mid-IR sources with fluxes S_{15} >= 3 mJy have an optical counterpart. The magnitude distribution of the sources shows a well defined peak at relatively bright magnitudes r~18. About 20% of the identified sources show a point-like morphology; its magnitude distribution has a peak at fainter magnitudes than those of galaxies. The mid-IR-to-optical and radio-to-optical flux diagrams are presented and discussed in terms of actual galaxy models. Objects with mid-IR-to-optical fluxes larger than 1000 are found that can only be explained as highly obscured star forming galaxies or AGNs. Blank fields being 8% of the 15 micron sample have even larger ratios suggesting that they may be associated with higher redshift and higher obscured objects.
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