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

Abstract

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 deg2 at 15 μm with ISOCAM and at 90 μm with ISOPHOT. Secondary surveys in other ISO bands were undertaken by the ELAIS team within the fields of the primary survey, with 6 deg2 being covered at 6.7 μm and 1 deg2 at 175 μm. 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 15 μm 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 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 AKARI FU-HYU galaxy evolution program: first results from the GOODS-N field

“…The ELAIS-N1 field was selected as part of the Extragalactic Large Area ISO Survey (ELAIS, Oliver et al (2000) ). The fields were selected on the basis of their high ecliptic latitude (β >40 • , to reduce the impact of zodiacal dust emission), low cirrus emission (I 100µm < 1.5 MJy/sr) and the absence of any bright (S 12µm > 0.6 Jy) IRAS 12µm sources.…”

ISOCAM observations in the Lockman Hole

“…The extension and depth of this survey is intermediate between the deep ISOCAM surveys (see e.g. Elbaz et al 1999) and the shallow and extended ELAIS survey (Oliver et al 2000). This allows us to obtain a sample of distant midinfrared sources that is large enough to study the deep universe without being biased by large scale structures.…”

“…The largest field surveyed during this program, already observed by the Röntgen Satellite (ROSAT, Hasinger et al 1993), is known as Lockman Hole since Lockman et al (1986) pointed out the existence of this exceptionally low HI absorption region. In the ISO data base, these surveys have been complemented on the deep side by the surveys on the Hubble Deep Field North (Serjeant et al 1997), the Hubble Deep Field South (Oliver et al 2002), the Canada-France Redshift Survey (Flores et al 1999), and by the lensed survey of Metcalfe et al (2003), and on the shallow side by the European Large Area Infrared Survey (ELAIS, Oliver et al 2000).…”

DRAO deep polarization study at 1.4 GHz

“…This area was selected for deep polarization imaging as a window on the extragalactic sky previously observed by ISO (Oliver et al 2000) and the Spitzer Wide Area Extragalactic Survey (SWIRE, Lonsdale et al 2003). This region is ideal for studies of the faint extragalactic polarized radio source population because of the large amount of data available at other frequencies that cover the ELAIS N1 region.…”