Observations of the Hubble Deep Field with the Infrared Space Observatory .1. Data reduction, maps and sky coverage

We present deep imaging at 6.7 and 15 mu m from the CAM instrument on the Infrared Space Observatory (ISO), centred on the Hubble Deep Field (HDF). These are the deepest integrations published to date at these wavelengths in any region of sky. We discuss the observational strategy and the data reduction. The observed source density appears to approach the CAM confusion limit at 15 mu m, and fluctuations in the 6.7-mu m sky background may be identifiable with similar spatial fluctuations in the HDF galaxy counts. ISO appears to be detecting comparable field galaxy populations to the HDF, and our data yield strong evidence that future infrared missions (such as SIRTF, FIRST and WIRE) as well as SCUBA and millimetre arrays will easily detect field galaxies out to comparably high redshifts

Observations of the Hubble Deep Field with the Infrared Space Observatory .4. Association of sources with Hubble Deep Field galaxies

We discuss the identification of sources detected by the Infrared Space Observatory (ISO) at 6.7 and 15 mu m in the Hubble Deep Field (HDF) region. We conservatively associate ISO sources with objects in existing optical and near-infrared HDF catalogues using the likelihood ratio method, confirming these results (and, in one case, clarifying them) with independent visual searches, We find 15 ISO sources to be reliably associated with bright [I-814(AB) < 23] galaxies in the HDF, and one with an I-814(AB)=19.9 star, while a further 11 are associated with objects in the Hubble Flanking Fields (10 galaxies and one star), Amongst optically bright HDF galaxies, ISO tends to detect luminous, star-forming galaxies at fairly high redshift and with disturbed morphologies, in preference to nearby ellipticals

Observations of the Hubble Deep Field with the Infrared Space Observatory .5. Spectral energy distributions, starburst models and star formation history

We have modelled the spectral energy distributions of the 13 Hubble Deep Field (HDF) galaxies reliably detected by the Infrared Space Observatory (ISO). For two galaxies the emission detected by ISO is consistent with being starlight or the infrared 'cirrus' in the galaxies. For the remaining II galaxies there is a clear midinfrared excess, which we interpret as emission from dust associated with a strong starburst. 10 of these galaxies are spirals or interacting pairs, while the remaining one is an elliptical with a prominent nucleus and broad emission lines. We give a new discussion of how the star formation rate can be deduced from the far-infrared luminosity, and derive star formation rates for these galaxies of 8-1000 phi M. yr(-1), where phi takes account of the uncertainty in the initial mass function, The HDF galaxies detected by ISO are clearly forming stars at, a prodigious rate compared with nearby normal galaxies, We discuss the implications of our detections for the history of star and heavy element formation in the Universe, Although uncertainties in the calibration, reliability of source detection, associations and starburst models remain, it is clear that dust plays an important role in star formation out to redshift 1 at least

Observations of the Hubble Deep Field with the Infrared Space Observatory .3. Source counts and P(D) analysis

We present source counts at 6.7 and 15 mu m from our maps of the Hubble Deep Field (HDF) region, reaching 38.6 mu Jy at 6.7 mu m and 255 mu Jy at 15 mu m. These are the first ever extragalactic number counts to be presented at 6.7 mu m, and are three decades fainter than IRAS at 12 mu m. Both source counts and a P(D) analysis suggest that we have reached the Infrared Space Observatory (ISO) confusion limit at 15 mu m: this will have important implications for future space missions. These data provide an excellent reference point for other ongoing ISO surveys. A no-evolution model at 15 mu m is ruled out at > 3 sigma, while two models which fit the steep IRAS 60-mu m counts are acceptable. This provides important confirmation of the strong evolution seen in IRAS surveys. One of these models can then be ruled out from the 6.7-mu M data

Observations of the Hubble Deep Field with the Infrared Space Observatory .2. Source detection and photometry

We present positions and fluxes of point sources found in the Infrared Space Observatory (ISO) images of the Hubble Deep Field (HDF) at 6.7 and 15 mu m. We have constructed algorithmically selected 'complete' flux-limited samples of 19 sources in the 15-mu m image, and seven sources in the 6.7-mu m image. The typical flux limit at 15 mu m is similar to 0.2 mJy and at 6.7 mu m is similar to 0.04 mJy. We have selected 'supplementary' samples of three sources at 15 mu m and 20 sources at 6.7 mu m by eye. We discuss the completeness and reliability of the connected pixel source detection algorithm used, by comparing the intrinsic and estimated properties of simulated data, and also by estimating the noise properties of the real data. The most pessimistic estimate of the number of spurious sources in the 'complete' samples is one at 15 mu m and two at 6.7 mu m, and in the 'supplementary' lists is one at 15 mu m and five at 6.7 mu m

Observations of the Hubble Deep Field with the Infrared Space Observatory .2. Source detection and photometry

We present positions and fluxes of point sources found in the Infrared Space Observatory (ISO) images of the Hubble Deep Field (HDF) at 6.7 and 15 μrn. We have constructed algorithmically selected ‘complete’ flux-limited samples of 19 sources in the 15-μm image, and seven sources in the 6.7-μm image. The typical flux limit at 15 μrn is <0.2 mJy and at 6.7 μrn is ∼0.04 mJy. We have selected ‘supplementary’ samples of three sources at 15 μurn and 20 sources at 6.7 μm by eye. We discuss the completeness and reliability of the connected pixel source detection algorithm used, by comparing the intrinsic and estimated properties of simulated data, and also by estimating the noise properties of the real data. The most pessimistic estimate of the number of spurious sources in the ‘complete’ samples is one at 15 μrn and two at 6.7 μrn, and in the ‘supplementary’ lists is one at 15 μrn and five at 6.7 μ.m