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We address the question of how to deal with confusion-limited surveys in the mid-infrared (MIR) domain by using information from shorter-wavelength observations over the same sky regions. Such information, once applied to apparently extended MIR sources, which are indeed ‘blends’ of two or more different sources, allow us to disentangle the single counterparts and to split the measured flux density into different components. We present the application of this method to the 24-μm Spitzer archival data in the Great Observatories Origins Deep Survey ELAIS-N1 (GOODS EN1) test field, where apparently extended, ‘blended’ sources constitute about 20 per cent of a reliable sample of 983 sources detected above the 5σ threshold down to 40 μJy. As a shorter-wavelength data set, we have considered the public Infrared Array Camera (IRAC) images and catalogues of the same field. We show that the 24-μm sample is almost unbiased down to ∼40 μJy and the careful application of the deblending procedure does not require any statistical completeness correction (at least at the flux level considered). This is probed by direct comparison of our results with results in the literature that analysed the same data set through extensive Monte Carlo simulations. The extrapolation of the source counts down to fainter fluxes suggests that our 24-μm sample is able to resolve ∼62 per cent of the cosmic background down to a flux level of 38 μJy. [ABSTRACT FROM AUTHOR]

We report on a search for the optical counterparts of selected sources from the Far-Infrared Background (FIRBACK) survey in the European Large Area ISO Survey (ELAIS) N2 field. Applying a likelihood ratio technique to optical catalogues from the Isaac Newton Telescope – Wide Field Survey (INT-WFS), we found optical identifications for 33 out of 55 FIRBACK sources in this field. These were then reassessed in the light of associations with the ELAIS final catalogue for the N2 field, to yield a final set of 31 associations. We have investigated the nature of this population through a comparison of their observed spectral energy distributions (SEDs) with predictions from radiative transfer models which simulate the emission from both cirrus and starburst components. We find the far-infrared sources to be 80 per cent starburst galaxies with their starburst component at a high optical depth. The resulting SEDs were used to estimate far-infrared luminosities, star formation rates (SFRs), dust temperatures and dust masses. The N2 FIRBACK population is found to consist of four suspected ultraluminous infrared galaxies (ULIRGs) with and , a number of luminous infrared galaxies (LIRGs) with moderate star formation rates and and a population of low-redshift quiescently star-forming galaxies. We also discuss the implications of these results for current evolutionary models. [ABSTRACT FROM AUTHOR]

We present the final analysis of the European Large AreaInfrared Space Observatory(ISO) Survey (ELAIS) 15-μm observations, carried out with the ISO Camera (ISOCAM) instrument on board theISO.The data-reduction method, known as the Lari Method, is based on a mathematical model of the behaviour of the detector and was specifically designed for the detection of faint sources in ISOCAM/ISO Photopolarimeter (ISOPHOT) data. The method is fully interactive and leads to very reliable and complete source lists.The resulting catalogue includes 1923 sources detected with signal-to-noise ratio ofin the 0.5–100 mJy flux range and over an area of 10.85 deg2 split into four fields, making it the largest non-serendipitous extragalactic source catalogue obtained to date from theISOdata.This paper presents the concepts underlying the data-reduction method together with its latest enhancements. The data-reduction process, the production and basic properties of the resulting catalogue are discussed. The catalogue quality is assessed by means of detailed simulations, optical identifications and comparison with previous analyses. [ABSTRACT FROM AUTHOR]

We present the multiwavelength properties and catalogue of the 15 μm and 1.4 GHz radio sources detected in the European Large AreaISOSurvey (ELAIS) areas N1 and N2. Using the optical data from the Wide Field Survey we use a likelihood ratio method to search for the counterparts of the 1056 and 691 sources detected at 15 μm and 1.4 GHz, respectively, down to flux limits ofand. We find that∼92 per cent of the 15 μmELAISsources have an optical counterpart down to. All mid-infrared (IR) sources with fluxeshave an optical counterpart. The magnitude distribution of the sources shows a well-defined peak at relatively bright magnitudes. The mid-IR-to-optical and radio-to-optical flux diagrams are presented and discussed in terms of actual galaxy models. About 15 per cent of the sources are bright galactic stars; of the extragalactic objects∼65 per cent are compatible with being normal or starburst galaxies and∼25 per cent active galactic nuclei (AGNs). Objects with mid-IR-to-optical fluxes larger than 100 are found, comprising∼20 per cent of the sample. We suggest that that these sources are highly obscured luminous and ultraluminous starburst galaxies and AGNs. [ABSTRACT FROM AUTHOR]

We present the optical identifications of a 95-μm ISOPHOT sample in the Lockman hole over an area of approximately half a deg2. The Rodighiero et al. catalogue includes 36 sources, making up a complete flux-limited sample for. Reliable sources were detected, with decreasing but well-controlled completeness, down to. We have combined mid-infrared (IR) and radio catalogues in this area to identify the potential optical counterparts of the far-IR sources. We found 14 radio and 13 15-μm associations, 10 of which have both associations. For the 11 sources with spectroscopic redshift, we have performed a spectrophotometric analysis of the observed spectral energy distributions (SEDs). Four of these 95-μm sources have been classified as faint IR (FIR) galaxies, six as luminous IR galaxies (LIRGs) and only one as an ultraluminous IR galaxy (ULIRG). We have discussed the redshift distribution of these objects, comparing our results with evolutionary model predictions 95 and 175μm. Given their moderate distances (the bulk of the closest spectroscopically identified objects lying at), their luminosities and star formation rates (SFR; median value), the sources unveiled by ISOPHOT at 95μm seem to correspond to the low redshiftFIRBACK 175-μm population, composed of dusty, star-forming galaxies with moderate SFRs. We computed and compared different SFR estimators, and found that the SF derived from the bolometric IR luminosity is well correlated with that computed from the radio and mid-IR fluxes. [ABSTRACT FROM AUTHOR]

This paper discusses the properties of the European Large AreaISOSurvey (ELAIS) 15-μm quasars and tries to establish a robust method of quasar selection for future use within theSpitzerWide-Area Infrared Extragalactic Survey (SWIRE) framework. The importance of good-quality ground-based optical data is stressed, both for the selection of candidates and for the estimation of photometric redshifts. Colour–colour plots and template fitting are used for these purposes. The properties of the 15-μm quasar sample, including variability and black hole masses, are studied and compared to the properties of other quasars that lie within the same fields but have no mid-infrared counterparts. The two subsamples do not present substantial differences and are believed to come from the same parent population. [ABSTRACT FROM AUTHOR]

In this paper, we present the results of calculations of cross-sections and rate coefficients for rotationally inelastic transitions in methanol (CH3OH), in its ground torsional state, induced by collisions with para-H2 in its ground rotational state. The interaction potential was calculated by means of many-body perturbation theory, and the corresponding cross-sections computed using the coupled states approximation to the Schrödinger equation for the CH3OH–H2 system. The rate coefficients have been calculated for kinetic temperatures in the range . We found that, although the rate coefficients for para-H2 are qualitatively similar to those computed for He, the collisional propensity rules are less pronounced when the perturber is para-H2 than when it is He. The rate coefficients for CH3OH–H2 tend to be larger than for CH3OH–He, a tendency which is anticipated from a comparison of the corresponding interaction potentials. Although our discussion is in terms of E-type methanol, the analogous results for A-type methanol and para-H2 are also available. Our calculations are the first to consider H2 as a collision partner for CH3OH and are directly relevant to the interpretation of observations of methanol in the interstellar medium. [ABSTRACT FROM AUTHOR]

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 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-μm sources and 75 per cent of the 6.7-μm 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 [∼10 per cent in 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 (log10 of 1–1000 μm luminosity ) 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 are genuine optically blank fields to : these must have very high infrared-to-optical ratios and probably have , so are high-luminosity dusty starbursts or Type 2 AGN. Nine hyperluminous infrared galaxies and nine extremely red objects (EROs) are found in the survey. The latter are interpreted as ultraluminous dusty infrared galaxies at . 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 , cool (cirrus-type SEDs) galaxies, with , implying . [ABSTRACT FROM AUTHOR]

Focuses on results of a new analysis of a deep 95 micrometer imaging survey of Lockman Hole for a far-infrared view of extra galactic sky. Parameters tested during the survey; Range to which the light source counts were estimated in the survey.

Cites a study published in 'Mon. Not. R. Astron. Soc,' which focuses on nature of the Infrared Space Observatory-selected sources on European Large Area Survey S2 region. Nature of sources responsible for observed strong evolution of sources at different density levels of stars; Basis of classification of galaxies.

The radio counterparts to the 15-µm sources in the European Large Area ISO Survey southern fields are identified in 1.4-GHz maps down to ∼80 µJy. The radio-mid-infrared correlation is investigated and derived for the first time at these flux densities for a sample of this size. Our results show that radio and mid-infrared (MIR) luminosities correlate almost as well as radio and far-infrared (FIR), at least up to z ... 0.6. Using the derived relation and its spread together with the observed 15-µm counts, we have estimated the expected contribution of the 15-µm extragalactic populations to the radio source counts and the role of MIR starburst galaxies in the well-known 1.4-GHz source excess observed at sub-mJy levels. Our analysis demonstrates that IR emitting starburst galaxies do not contribute significantly to the 1.4-GHz counts for strong sources, but start to become a significant fraction of the radio source population at flux densities ...0.5-0.8 mJy. They are expected to be responsible for more than 60 per cent of the observed radio counts at ...0.05 mJy. These results are in agreement with the existing results on optical identifications of faint radio sources. [ABSTRACT FROM AUTHOR]

Abstract We present the 15-μm extragalactic source counts from the Final Analysis Catalogue of the European Large Area ISO Survey (ELAIS) Southern hemisphere field S1, extracted using the Lari method. The large number of extragalactic sources (∼350) detected over this area between about 0.5 and 100 mJy guarantee a high statistical significance of the source counts in the previously poorly covered flux density range between IRAS and the Deep ISOCAM Surveys. The bright counts in S1 (S[sub 15 μm]≳ 2 mJy) are significantly lower than other published ISOCAM counts in the same flux range and are consistent with a flat, Euclidean slope, suggesting the dominance of a non-evolving population. In contrast, at fainter fluxes (S[sub 15 μm]≲ 2 mJy) our counts show a strong departure from no-evolution models, with a very steep super-Euclidean slope down to our flux limit (∼0.5 mJy). Strong luminosity and density evolutions of the order of, respectively, L∝ (1 +z)[sup 3.0] and ρ∝ (1 +z)[sup 3.5] are needed at least for the population of star-forming galaxies in order to fit the counts and the redshift distributions observed at different fluxes. A luminosity break around 10[sup 10.8]L[sub ⊙] must be introduced in the local luminosity function of starburst galaxies in order to reproduce our sharp increase of the counts below 2 mJy and the redshift distributions observed for 15-μm sources at different flux levels. The contribution of the strongly evolving starburst population (down to 50 μJy) to the 15-μm cosmic background is estimated to be ∼2.2 nW m[sup -2] sr[sup -1], which corresponds to ∼67 per cent of the total mid-infrared background estimate. [ABSTRACT FROM AUTHOR]

We present the 15-µm luminosity function of type 1 active galactic nuclei (AGN1; quasi-stellar object + Seyfert 1). Our sample of 21 high-redshift sources is selected from the Preliminary Analysis catalogue in the S1 field of the European Large Area ISO Survey (ELAIS). To study the cosmological evolution of the AGN1 luminosity function, our sample has been combined with a local sample of 41 sources observed by IRAS. We find that the luminosity function of AGN1 at 15 µm is fairly well represented by a double-power-law-function. There is evidence for significant cosmological evolution consistent with a pure luminosity evolution (PLE) model L(z) ∝ (1 + z)[sup k[sub L]], with k[sub L] = 3.0-3.3. The value of k[sub L] depends on the existence or non-existence of an evolution cut-off at redshift ∼2, and on the adopted cosmology. From the luminosity function and its evolution we estimate a contribution of AGN1 to the cosmic infrared background (CIRB) of νI[sub ν] ∼ 6 x 10[sup -11] W m[sup -2] sr[sup -1] at 15 µm. This corresponds to ∼-2-3 per cent of the total observed CIRB at this wavelength. Under the usual assumptions of unified models for AGN, the expected contribution of the whole AGN population to the CIRB at 15 µm is 10-15 per cent. [ABSTRACT FROM AUTHOR]

We develop a new data reduction technique for ISOCAM LW data and apply it to the European Large Area ISO Survey (ELAIS) LW3 (15-μm) observations in the southern hemisphere (S1). This method, known as LARI technique and based on the assumption of the existence of two different time-scales in ISOCAM transients (accounting for either fast or slow detector response), is particularly designed for the detection of faint sources. In the ELAIS S1 field we obtain a catalogue of 462 15-μm sources with signal-to-noise ratios ≥5 and flux densities in the range 0.45–150 mJy (filling the whole flux range between the Deep ISOCAM Surveys and the IRAS Faint Source Survey). The completeness at different flux levels and the photometric accuracy of this catalogue are tested with simulations. Here we present a detailed description of the method and discuss the results obtained by its application to the S1 LW3 data. [ABSTRACT FROM AUTHOR]