Efstathiou, Andreas

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 μm. 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 μm is ∼0.2 mJy and at 6.7 μm is ∼0.04 mJy. We have selected 'supplementary' samples of three sources at 15 μm 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 μm and two at 6.7 μm, and in the 'supplementary' lists is one at 15 μm and five at 6.7 μm.

We present preliminary source counts at 6.7 and 15 μm from the preliminary analysis of the European Large Area ISO Survey, with limiting flux densities of ∼2mJy at 15 μm and ∼1 mJy at 6.7 μm. We separate the stellar contribution from the extragalactic using identifications with automated plate measurement sources made with the likelihood ratio technique. We quantify the completeness and reliability of our source extraction using (a) repeated observations over small areas, (b) cross-identifications with stars of known spectral type, (c) detections of the point spread function wings around bright sources and (d) comparison with independent algorithms. Flux calibration at 15 μm was performed using stellar identifications; the calibration does not agree with the pre-flight estimates, probably due to effects of detector hysteresis and photometric aperture correction. The 6.7-μm extragalactic counts are broadly reproduced in the Pearson & Rowan-Robinson model, but the Franceschini et al. model underpredicts the observed source density by ∼0.5-1 dex, although the photometry at 6.7 μm is still preliminary. At 15 μm the extragalactic counts are in excellent agreement with the predictions of the Pearson & Rowan-Robinson. Franceschini et al., Guiderdoni et al. models and the evolving models of Xu et al., over seven orders of magnitude in 15-μm flux density. The counts agree with other estimates from the ISOCAM instrument at overlapping flux densities, provided a consistent flux calibration is used. Luminosity evolution at a rate of (1 + z)3, incorporating mid-infrared spectral features, provides a better fit to the 15-μm differential counts than (1 + z)4 density evolution. No-evolution models are excluded, implying that below around 10mJy at 15 μm the source counts become dominated by an evolving cosmological population of dust-shrouded starbursts and/or active galaxies.

We discuss optical associations, spectral energy distributions (SEDs), and photometric redshifts for Spitzer Wide-Area Infrared Extragalactic (SWIRE) Survey sources in the European Large-Area ISO Survey (ELAIS) N1 area and the Lockman Validation Field (VF). The band-merged Infrared Array Camera (IRAC) (3.6,4.5,5.8, and 8.0 μm) and Multiband Imaging Photometer for Spitzer (24, 70, and 160 μm) data have been associated with optical UgriZ data from the Isaac Newton Telescope Wide Field Survey in ELAIS N1 and with our own optical Ugri data in Lockman-VF. Criteria for eliminating spurious infrared sources and for carrying out star-quasar-galaxy separation are discussed, and statistics of the identification rate are given. Thirty-two percent of sources in the ELAIS N1 field are found to be optically blank (to r = 23.5) and 16% in Lockman-VF (to r = 25). The SEDs of selected ELAIS sources in N1 detected by SWIRE, most with spectroscopic redshifts, are modeled in terms of a simple set of galaxy and quasar templates in the optical and near-infrared (NIR), and with a set of dust emission templates (cirrus, M82 starburst, Arp 220 starburst, and active galactic nucleus [AGN] dust torus) in the mid-infrared. The optical data, together with the IRAC 3.6 and 4.5 μm data, have been used to determine photometric redshifts. For galaxies with known spectroscopic redshifts, there is a notable improvement in the photometric redshift when the IRAC data are used, with a reduction in the rms scatter from 10% in (1 + z) to 7%. Although further spectroscopic data are needed to confirm this result, the prospect of determining good photometric redshifts for much of the SWIRE survey, expected to yield over 2 million extragalactic objects, is excellent. Some modifications to the optical templates were required in the previously uninvestigated wavelength region 2-5 μm. The photometric redshifts are used to derive the 3.6 and 24 μm redshift distribution and to compare this with the predictions of models. For those sources with a clear mid-infrared excess, relative to the galaxy starlight model used for the optical and NIR, the mid- and far-infrared data are modeled in terms of the same dust emission templates (cirrus, M82, Arp 220, and AGN dust torus). The proportions found of each template type are cirrus, 31%; M82, 29%; Arp 220,10%; and AGN dust tori, 29%. The distribution of the different infrared SED types in the L IR/L opt versus L IR plane, where L IR and L opt are the infrared and optical bolometric luminosities, respectively, is discussed. There is an interesting population of luminous cool cirrus galaxies with L IR > L opt, implying a substantial dust optical depth. Galaxies with Arp 220-like SEDs, of which there are a surprising preponderance compared with preexisting source count models, tend to have high ratios of infrared to optical bolometric luminosity, consistent with having very high extinction. There is also a high proportion of galaxies whose mid-infrared SEDs are fitted by an AGN dust torus template (29%). Of these only 8% of these are type 1 AGNs according to the optical-NIR template fitting, whereas 25% are fitted with galaxy templates in the optical-NIR and have L IR > L opt and so have to be type 2 AGN. The remainder have L IR < L opt and so can be Seyfert galaxies, in which the optical AGN fails to be detected against the light of the host galaxy. The implied dust covering factor, ≥75%, is much higher than that inferred for bright optically selected quasars.

We complement our previous analysis of a sample of z ~ 1-2 luminous and ultraluminous infrared galaxies [(U)LIRGs], by adding deep Very Large Array radio observations at 1.4 GHz to a large data set from the far-UV to the submillimetre, including Spitzer and Herschel data. Given the relatively small number of (U)LIRGs in our sample with high signal-to-noise (S/N) radio data, and to extend our study to a different family of galaxies, we also include six wellsampled near-infrared (near-IR)-selected BzK galaxies at z ~ 1.5. From our analysis based on the radtran spectral synthesis code GRASIL, we find that, while the IR luminosity may be a biased tracer of the star formation rate (SFR) depending on the age of stars dominating the dust heating, the inclusion of the radio flux offers significantly tighter constraints on SFR. Our predicted SFRs are in good agreement with the estimates based on rest-frame radio luminosity and the Bell calibration. The extensive spectrophotometric coverage of our sample allows us to set important constraints on the star formation (SF) history of individual objects. For essentially all galaxies,we find evidence for a rather continuous SFR and a peak epoch of SF preceding that of the observation by a few Gyr. This seems to correspond to a formation redshift of z ~ 5-6. We finally show that our physical analysis may affect the interpretation of the SFR-M* diagram, by possibly shifting, with respect to previous works, the position of the most dust obscured objects to higher M* and lower SFRs.

We discuss the identification of sources detected by the Infrared Space Observatory (ISO) at 6.7 and 15 μm 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 [I814 (AB) < 23] galaxies in the HDF, and one with an I814(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.

We present results from a deep mid-infrared survey of the Hubble Deep Field South (HDF-S) region performed at 6.7 and 15 μm with the ISOCAM instrument on board the Infrared Space Observatory (ISO). The final map in each band was constructed by the co-addition of four independent rasters, registered using bright sources securely detected in all rasters, with the absolute astrometry being defined by a radio source detected at both 6.7 and 15 μm. We sought detections of bright sources in a circular region of radius 2.5 arcmin at the centre of each map, in a manner that simulations indicated would produce highly reliable and complete source catalogues using simple selection criteria. Merging source lists in the two bands yielded a catalogue of 35 distinct sources, which we calibrated photometrically using photospheric models of late-type stars detected in our data. We present extragalactic source count results in both bands, and discuss the constraints that they impose on models of galaxy evolution, given the volume of space sampled by this galaxy population.

IR spectroscopy in the range 12–230 μm with the SPace IR telescope for Cosmology and Astrophysics (SPICA) will reveal the physical processes governing the formation and evolution of galaxies and black holes through cosmic time, bridging the gap between the James Webb Space Telescope and the upcoming Extremely Large Telescopes at shorter wavelengths and the Atacama Large Millimeter Array at longer wavelengths. The SPICA, with its 2.5-m telescope actively cooled to below 8 K, will obtain the first spectroscopic determination, in the mid-IR rest-frame, of both the star-formation rate and black hole accretion rate histories of galaxies, reaching lookback times of 12 Gyr, for large statistically significant samples. Densities, temperatures, radiation fields, and gas-phase metallicities will be measured in dust-obscured galaxies and active galactic nuclei, sampling a large range in mass and luminosity, from faint local dwarf galaxies to luminous quasars in the distant Universe. Active galactic nuclei and starburst feedback and feeding mechanisms in distant galaxies will be uncovered through detailed measurements of molecular and atomic line profiles. The SPICA’s large-area deep spectrophotometric surveys will provide mid-IR spectra and continuum fluxes for unbiased samples of tens of thousands of galaxies, out to redshifts of z ∼ 6.

We present preliminary results of multi-object spectroscopy of new mid-, and far-infrared selected galaxies detected in the European Large Area ISO Survey (ELAIS). The data have been obtained with the fibre spectrographs WYFFOS at the William Herschel Telescope (Observatorio del Roque de los Muchachos, ORM, Canary Islands) and Hydra at the WIYN Telescope (Kitt Peak Observatory, Arizona). The sample includes ISO sources detected at 7, 15 and 90 μm and radio sources from our deep VLA survey in the ELAIS areas.

We present the 90-μm luminosity function of the Final Analysis of the European Large Area ISO Survey (ELAIS), extending the sample size of our previous analysis (Paper IV) by about a factor of 4. Our sample extends to z = 1.1, ∼50 times the comoving volume of Paper IV, and 10 7.7 < h -2 L/L ⊙ < 10 02.5. From our optical spectroscopy campaigns of the northern ELAIS 90-μm survey (7.4 deg 2 in total, to S 90 μm ≥ 70 mJy), we obtained redshifts for 61 per cent of the sample (151 redshifts) to B < 21 identified at 7 μm, 15 μm, 20 cm or with bright (B < 18.5) optical identifications. The selection function is well-defined, permitting the construction of the 90-μm luminosity function of the Final Analysis catalogue in the ELAIS northern fields, which is in excellent agreement with our Preliminary Analysis luminosity function in the ELAIS S1 field from Paper IV. The luminosity function is also in good agreement with the recent IRAS-based prediction of Serjeant and Harrison - which, if correct, requires luminosity evolution of (1 + z) 3.4±1.0 for consistency with the source counts. This implies an evolution in comoving-volume-averaged star formation rate at z ≲ 1 consistent with that derived from rest-frame optical and ultraviolet surveys.