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The European Large Area ISO Survey: optical identifications of 15-μm and 1.4-GHz sources in N1 and N2
We present the multiwavelength properties and catalogue of the 15μmand 1.4GHz radio sources detected in the European Large Area ISO Survey(ELAIS) areas N1 and N2. Using the optical data from the Wide FieldSurvey we use a likelihood ratio method to search for the counterpartsof the 1056 and 691 sources detected at 15μm and 1.4GHz,respectively, down to flux limits of S15= 0.5mJy andS1.4GHz= 0.135mJy. We find that ~92 per cent of the 15μmELAIS sources have an optical counterpart down to r'= 24. Allmid-infrared (IR) sources with fluxes S15>= 3mJy have anoptical counterpart. The magnitude distribution of the sources shows awell-defined peak at relatively bright magnitudes r'~ 18. Themid-IR-to-optical and radio-to-optical flux diagrams are presented anddiscussed in terms of actual galaxy models. About 15 per cent of thesources are bright galactic stars; of the extragalactic objects ~65 percent are compatible with being normal or starburst galaxies and ~25 percent active galactic nuclei (AGNs). Objects with mid-IR-to-opticalfluxes larger than 100 are found, comprising ~20 per cent of the sample.We suggest that that these sources are highly obscured luminous andultraluminous starburst galaxies and AGNs.
| 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 μm, and the associated data at U,g', r', i', Z, J, H, K and 20 cm. The origin of the survey, infrared andradio observations, data-reduction and optical identifications arebriefly reviewed, and a summary of the area covered and the completenesslimit for each infrared band is given. A detailed discussion of theband-merging and optical association strategy is given. The totalCatalogue consists of 3762 sources. 23 per cent of the 15-μm sourcesand 75 per cent of the 6.7-μm sources are stars. For extragalacticsources observed in three or more infrared bands, colour-colour diagramsare presented and discussed in terms of the contributing infraredpopulations. Spectral energy distributions (SEDs) are shown for selectedsources and compared with cirrus, M82 and Arp220 starburst, and activegalactic nuclei (AGN) dust torus models.Spectroscopic redshifts are tabulated, where available. For the N1 andN2 areas, the Isaac Newton Telescope ugriz Wide Field Survey permitsphotometric redshifts to be estimated for galaxies and quasars. Theseagree well with the spectroscopic redshifts, within the uncertainty ofthe photometric method [~10 per cent in (1 +z) for galaxies]. Theredshift distribution is given for selected ELAIS bands andcolour-redshift diagrams are discussed.There is a high proportion of ultraluminous infrared galaxies(log10 of 1-1000 μm luminosity Lir > 12.22)in the ELAIS Catalogue (14 per cent of 15-μm galaxies with known z),many with Arp220-like SEDs. 10 per cent of the 15-μm sources aregenuine optically blank fields to r'= 24: these must have very highinfrared-to-optical ratios and probably have z > 0.6, so arehigh-luminosity dusty starbursts or Type 2 AGN. Nine hyperluminousinfrared galaxies (Lir > 13.22) and nine extremely redobjects (EROs) (r-K > 6) are found in the survey. The latter areinterpreted as ultraluminous dusty infrared galaxies at z~ 1. The largenumbers of ultraluminous galaxies imply very strong evolution in thestar formation rate between z= 0 and 1. There is also a surprisinglylarge population of luminous (Lir > 11.5), cool(cirrus-type SEDs) galaxies, with Lir-Lopt > 0,implying AV > 1.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
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