Showing papers by "T. J. Sumner published in 1997"

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

Abstract: We have modelled the spectral energy distributions of the 13 Hubble Deep Field (HDF) galaxies reliably detected by the Infrared Space Observatoiy (ISO). For two galaxies the emission detected by ISO is consistent with being starlight or the infrared 'cirrus' in the galaxies. For the remaining 11 galaxies there is a clear mid-infrared 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 8-1000o M? yr-1, where o 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 - III. Source counts and P(D) analysis

Abstract: We present source counts at 6.7 and 15 μm from our maps of the Hubble Deep Field (HDF) region, reaching 38.6 μJy at 6.7 μm and 255 μJy at 15 μm. These are the first ever extragalactic number counts to be presented at 6.7 μm, and are three decades fainter than IRAS at 12 μm. Both source counts and a P(D) analysis suggest that we have reached the Infrared Space Observatory (ISO) confusion limit at 15 μrn; 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 μrn is ruled out at > 3σ, while two models which fit the steep IRAS 60-μm 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-μm data.

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

Abstract: 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.

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

Abstract: We present deep imaging at 6.7 and 15 μm 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 μm, and fluctuations in the 6.7-μm 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 - II. Source detection and photometry

Abstract: 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.

Electrostatic charging of the LISA proof masses

Abstract: The build-up of electrical charge on the proof masses is an important disturbance for LISA. The charging is due to penetrating particle radiation (primarily protons) from cosmic rays, and from the Sun during solar flares. Estimates of charging rates have been computed using the GEANT Monte Carlo particle-transport code in combination with realistic proton flux models. The consequences of the charging are discussed.

Fluctuations in the Diffuse Soft X-ray Background; Probably of Galactic Halo Origin

Abstract: Soft X-ray background data from the ROSAT PSPC have been fitted by a model including emission from the local bubble, embedded hot gas within the disk, hot gas in the Galactic halo and extra-galactic emission, together with local and disk absorption. In all directions a halo component at 106.2 K (0.2 keV) is required for an acceptable fit. The halo emission measure shows spatial variability and the global trend suggests a disk-like planar rather than more extended spherical distribution. New values for the emission measure within the local bubble are derived.