Taking ISO to the limits: exploring the faintest sources in the infrared

(Feb 3 - 4, 1997, ESAC, Madrid, Spain)


Title: A search for brightness fluctuations in the Zodiacal Light at 25 micron (Oral)

Authors and affiliation: P. Abraham, Ch. Leinert, D. Lemke Max-Planck-Institut fuer Astronomie


At wavelengths shorter than 60 micron Zodiacal Light constitutes the main component of foreground/background radiation. Its variation at small spatial scales provides a natural detection limit for faint source observations. We mapped at 25 micron three ~0.5degx0.5deg fields at low, intermediate and high ecliptic latitude with ISOPHOT. No structures were seen in these small samples of zodiacal light. The pixel-to-pixel signal variations are dominated by the drift of detector response and by the repeatibility of the measurement. After best-effort correction for these effects, for an aperture of 3 arcmin we find an upper limit for the underlying rms brightness fluctuations of +-0.5%. This limit on the percentage fluctuation can be used for estimation of the detection limit for very faint point sources.

Title: PHT-S advanced data reduction: PHT-S drift corrections on faint sources (Oral)

Authors and affiliation: Jose A. Acosta-Pulido ISOPHOT IDT, ISO Science Operations Centre, Vilspa Joseph Schubert MPIA-Heidelberg


Infrared detectors are known to show a highly non-linear transient response to step changes of illumination. This response is characterised by a long relaxation time and thus by memory of the previous flux history. In this contribution we will apply to the observations a physical model (Fouks' model) which can accurately describe the behaviour of the detector ISOPHOT-S. Using in-orbit data we have confirmed the validity of the parameter function derived during the ground calibration. We will describe the effects on the measurement of faint sources, using chopped and staring modes. We will show that the flux can be underestimated by up to 40%, even for apparently stable measurements. The applicability of this model to the detector P2 will be also discussed.

Title: Space Weather (Oral)

Authors and affiliation: Hector Castaneda ISO SOC/VILSPA


In the space environment in which ISOPHOT operates the high-energy radiation affects the performance of the detectors. Curing procedures have been designed to restore the photometric calibrations of the detectors after passage by the Van Allen belts, that are monitored via measurements (responsivity checks) at the end of the procedures. A study of the behaviour of the ISOPHOT detectors during the performance checks at activation and de-activation is presented. A clear correlation is established between the changes in the responsivity of the FIR detectors P3, C100, and C200 and the activity known as geomagnetic storms. The PHT-S detectors is also affected for this activity.

Title: A Search for an optical/ISO flux correlation in the Hubble Deep Field (Oral)

Authors and affiliation: D. Clements, IAS, ISOHDF Team IC and elsewhere


We examine the ISOHDF rasters for evidence of any correlation between the optical flux, as revealed by the HST observations, and the 7 and 15 micron flux as measured by the ISO. Initial analysis shows tentative evidence for correlations in both wavelengths. However, when these results are compared with similar analyses performed on randomised galaxy catalogues, the two are found to be indistinguishable. We thus conclude that there is no evidence to support the existance of mid-IR/optical correlation in this data. It is likely that a larger region than the HDF is needed for a definitive study of this question.

Title: ISOCAM data reduction techniques for deep survey of faint sources (Oral)

Authors and affiliation: D'esert F.-X. and Puget J.-L IAS


We describe the methods which we currently use to detect and measure weak sources on a strong foreground with ISOCAM central programme observations, mainly for the various extragalactic deep surveys. These data are more difficult to analyse than large CCD optical format because glitch and memory effects on the detector have so far prevented the use of a given flat-field. A temporal analysis of the signal is needed before the data are projected onto the sky. These methods are still preliminary. The processing chronology is: 1)reading data, appending satellite pointing information and subtracting a dark frame, 2)detection and removal of fast glitches, 3)detection and removal of slow glitches, 4)finding the best value and its associated error of each CAM pixel for each raster position (beam-switching technique so far), 5)projecting and coadding the reduced data on the sky, 6)extracting point sources, 7)testing the reproducibility of a given candidate in the various redundant surveys. We think that after a complete and appropriate processing, the ultimate performance of the camera will not be limited by the so--called flat field errors and that it will be close to optimal.

Title: Observing faint IR excesses from Main sequnce stars (Oral)

Authors and affiliation: The HJHVEGA consortium. PI H. Habing, Speaker C. Dominik Leiden Observatory/ISO Vilspa/LAEFF


The HJHVEGA proposal studies near-by main sequence stars in order to detect Excess radiation at IR wavelengths. In contrast to other proposals on the subject, we are also taking data at longer wavelength, out to 180um. At these wavelengths, background (cirrus) confusion plays an important role. The original set-up of the observations with chopped measurements, in particular with the C200, proved to be not successful. Changing the observation mode to a small map has shown a significant improvement, with only a small observation time penalty.

Title: Faint Source Detection in the ISOCAM Deep Survey (Oral)

Authors and affiliation: David Elbaz CEA/DAPNIA/SAp


I will present the method used at the Service d'Astrophysique to detect faint objects in the Lockman Hole, an "empty field" selected for its low galactic IR emission. This new method is based on a multi-resolution wavelet analysis. The Deep Survey covers a field of 20'x20' with 2 sets of overlapping rasters with an internal redundancy of 3. A given "sky pixel" was observed by 6 different pixels of the camera, corresponding to 11 min and 18 min per "sky pixel" for respectively 15 and 6.75 microns.

Title: PHT observations of a sample of compact steep-spectrum radio galaxies (Oral)

Authors and affiliation: C. Fanti, R. Fanti. F.Pozzi Dipartimento di Fisica dell'Universita' and Istituto di Radioastronomia Bologna


Compact steep-spectrum radio sources (CSSs) have very small (apparent) linear size and yet have a steep radio spectrum. They represent a large fraction (15-30%) of the radio sources in a flux limited complete sample. It has been proved that the majority of CSSs are physically much smaller than their host galaxy, their sizes being sometimes smaller than 1kpc. Two competing theories are invoked to explain the nature of such objects: - the "youth" scenario, in which CSSs are indeed the young phase of the classical double radio sources (like Cygnus A). - the "frustration" scenario, in which CSSs are objects as old as their larger relatives, in which the radio plasmoids are trapped by an interstellar medium much denser than usual. If more gas is present, it is expected that also more cold dust should be present. The latter should be revealed by ISO at long wavelengths. To test these two models we are observing a sample of about 25 CSS galaxies and a matched sample of large size radio galaxies to check whether CSSs have indeed different properties than regular radio galaxies. From the few observations obtained so far (about 30% of the whole sample) we find no difference between the two class of objects, no source being detected. This result, if confirmed by the completion of the experiment, would prove that the "youth" scenario is the most likely one.

Title: The ISOPHOT Interactive Analysis (PIA), a calibration and scientific analysis tool. (Poster)

Authors and affiliation: Carlos GABRIEL ESA-SAI


The ISOPHOT Interactive Analysis (PIA), is a calibration, scientific analysis and visualization tool for accessing and processing ISOPHOT data. ISOPHOT is one of the instruments on board the Infrared Space Observatory ISO, launched in November 1995 by the European Space Agency. PIA is an IDL based package, comprising around 1700 routines including a user friendly graphical interface. All the capabilities of input/output, processing and visualization can be reached from window menus, for all the different ISOPHOT sub-systems in all the different levels of data reduction. This applies, starting from digital raw data, coming from the ISO telemetry, to the final level of calibrated images, spectra, multi-filter, multi-aperture photometry. Documentation is written in hypertext format, and can be used on-line through a browser of the user's choice and from the PIA. PIA is distributed freely to all astronomers wishing to use it for ISOPHOT data reduction and analysis. The package is available for various platforms running IDL (from version 3.6 on), its installation is extremely simple.

Title: PHT Faint Source Data Reduction (Oral)

Authors and affiliation: Martin Haas MPIA Heidelberg


Special treatments and data reduction strategies are presented to improve the S/N for PHT faint source observations. These include deglitching, flatfielding, drift and correction factors for chopped measurements.

Title: Deep ISOPHOT observations of Supernova Remnants (Oral)

Authors and affiliation: Ingolf Heinrichsen (currently Vilspa) Max-Planck Institut fuer Kernphysik Richard Tuffs Max-Planck Institut fuer Kernphysik Deborah Levine ISO Science Operations Team/IPAC


First scientific results of ISOPHOT observations of the type II oxygenrich supernova remnant MSH11-54 (G292.0+1.8) will be presented. The spectrophotometric PHT-S results will be compared to results obtained for the class prototype Cassiopeia-A. The morphology of MSH11-54 as seen in an ISOPHOT P32 60micron map will be discussed with respect to available Radio, Einstein X-ray and IRAS HIRES images. PHT-P wide beam photometry has been obtained at the X-ray maximum and at the maximum of the FIR emission. A comparision with IRAS results is presented and the problems encountered with the calibration of PHT-P photometry of faint extended objects. Special emphasis will be put on the data reduction of deep PHT-S raster observations on Cassiopeia-A and the improvements made in data processing and calibration accuracy achieved over the last months.

Title: ISOPHOT observations of Cirrus (Oral)

Authors and affiliation: Uwe Herbstmeier(1), Peter Abraham(1), Rene Laureijs(2) Dietrich Lemke(1), Kalevi Mattila(3), Christoph Leinert (1), Christian Surace(1) 1: Max-Plank-Institut fuer Astronomie 2: ESA - ISO Spacecraft Operation Centre 3: University of Helsinki


We will present the results of ISOPHOT observations towards four cirrus fields in the wavelength range 90 - 180 micron addressing the cirrus confusion noise. The brightness of the structures span a range of about one order of magnitude. We check the dependence of the cirrus noise from the mean brighness of the fields and the wavelength to estimate the limiting cirrus noise value for low brightness regions. The results will be compared with predictions from the literature. These predictions are based on assumptions concerning the spatial frequency power spectrum of the brightness. We will address the question whether the actual power spectra fit to these assumptions.

Title: Searching For BOK globules using the ISSA plates (Poster)

Authors and affiliation: Nick Jessop and Derek Ward Thompson.


I will discuss how one might attempt to identify Bok globules and areas of isolated star formation using the IRAS Sky Survey Atlas. Preliminaryu results on a technique for identifying background regions for use in absolute photometry will be presented.

Title: ISOPHOT Observations of a Sample of Blue Compact Galaxies (Oral)

Authors and affiliation: Norbert Junkes, Gotthard Richter, Rob Assendorp (AIP Potsdam), Harald Krueger (MPIK Heidelberg), Alexej Kniazev, Valentin Lipovetsky (SAO, Nizhnij Arkhyz, Russia)


Blue Compact Galaxies are explained as star formation bursts in old un- evolved galaxies of primordial gas clouds. They are therefore of considerable interest for the formation and evolution of galaxies. Many of the open prob- lems in the present knowledge of their nature are connected with phenomena which manifest themselves in the IR range. Whereas some individual BCGs are observed extensively, there is a lack of systematic observations of well defined statistical samples. We have selected an unbiased sample of BCGs from an objective prism survey by well defined criteria (high excitation HII region characteristics), for which complete data on element abundances, radial velocities and UBVR photometry are available. For these galaxies we have performed IR broadband photometry in 4 bands (12mu, 25mu, 60mu, 100mu) with ISO, and will present first results. Supplementary optical CCD, near- infrared (JHK) and radio observations are planned. Most of the objects in our list have not been detected by IRAS, and very few of them in only one band (60mu).

Title: ISOPHOT Far-Infrared Survey in the Lockman Hole and High-redshift Quasars seen by ISO (Oral)

Authors and affiliation: K. Kawara et al.


The results obtained from the Lockman Hole survey with ISOPHOT and ISOPHOT photometry of high-redshift qusars are presented. The PHT22 raster mapping mode was used. The observational strategy is discussed for faint source detections.

Title: General observing strategies and overview on PHT calibration status

Authors and affiliation: U. Klaas (MPIA, ISO-SOC), PIDT Vilspa & PHT team MPIA


We present a list of recommendations for faint source observing strategies with ISOPHOT. The recommendations are based on the test measurements presented elsewhere at this workshop (Abraham et al.) and investigations of various PHT faint source programs. We discuss an extension of the PHT raster mode recently included into PGA to enable slow telescope nodding. An overview of currently known instrumental effects affecting the calibration of faint source measurements is presented. We give the status of the PHT calibration. Future steps in the establishment of calibration correction factors are outlined.

Title: ISOPHOT Instrument Overview (Oral)

Authors and affiliation: D. Lemke, Max-Planck Institute for Astronomy, Heidelberg


Lessons learnt in-flight on the susceptibility of 4 different detector types, which cover the wavelength range 2.5 ... 240 micron, to cosmic particles and on the curing of radiation damage, will be reported. The flux calibration has to include corrections for non-linearities of detectors and preamps, memory and drift effects, as well as the continuous radiation induced responsivity increases of the detectors along the orbit. At the longest wavelength sky confusion noise imposes a detection limit. Examples of faint source observations and sensitivity values which are practically achievable will be presented. Efforts to improve further the calibration accuracy and the detection limits are progressing.

Title: Faint sources in the Virgo Cluster observed with PHT32 (Oral)

Authors and affiliation: S.Niklas & R.Tuffs, Max-Planck-Institut fuer Kernphysik


A sample of 62 late-type galaxies in the Virgo Cluster have been observed with ISOPHOT at 60, 100 and 175 mu using the PHT32 AOT. The faintest galaxy detected has an optical magnitude of B_T = 17. In order to improve the detection statistics and the signal-to-noise ratio correction for long-term detector drift and vignetting have been derived and apllied to the data.

Title: 1: ISO observations of Hubble Deep Field (Oral)

Authors and affiliation: Seb Oliver (speaker) & The ISO HDF Consortium


We have obtained ISO Observations at 6.7 and 15 micron of the Hubble Deep Field. These are the deepest ISO observations to date. We Located 27 sources at 6.7 micron and 22 at 15 micron, with typical fluxes of 0.04 mJy and 0.2 mJy respectively. 14 of the sources are within the HDF proper and have spectroscopic or photometric redshifts. Most of these have strong infrared excess indicative of very active starformation. This interpretation has important implications for the history of starformation.

Title: 2: The European Large Area ISO Survey (ELAIS) (Poster)

Authors and affiliation: Seb Oliver & The ELAIS Consortium


ELAIS is a project to survey 13 square degrees of the high galactic latitude sky at 15 and 90 microns with the Infrarred Space Observatory. We expect to reach sensitivities of 2 mJy at 15 microns and 50 mJy at 90 micron. With such sensitivities we expect to detect around a thousand star forming galaxies similar to those seen by IRAS but to much higher redshifts, thus probing the cosmological history of star formation. In particular we hope to able to uncover more examples of the ultra and hyper luminous galaxies exemplified by IRAS F10214+4724. In addition we expect to detect hundreds of AGN, thousands of stars and many more normal galaxies.

Title: ISOPHOT observations of the far-infrared luminous galaxy IRAS 13224-3809g (Poster)

Authors and affiliation: M. Polletta, T. Courvoisier, R. Walter Integral Science Data Center, Versoix, Switzerland


ISOPHOT observations from mid to far infrared of the Narrow-Line Seyfert 1 galaxy IRAS 13224-3809 are reported. This source has been detected by IRAS with a luminosity L(40-120 microms) = 4.e11 L(Sun). ISO fluxes are lower than IRAS fluxes of a factor >2.6. This difference cannot be simply explained by the different apertures of the two instruments. Since IRAS 13224-3809 is a well known variable source at high energies (X-ray), we are considering this characteristic as possible explanation of this difference. We plan to re-observe this source with ISO about one year after the first ISO observation. We remark large uncertainties in ISOPHOT because of uncertainties in calibration. The comparison between fluxes computed using the default responsivity and the responsivities obtained by the internal Fine Calibration Sources gives, in some case, a difference by a factor larger than 3. The flux we have used here is derived using the lowest responsivity. The factor between the IRAS and ISO fluxes is therefore certainly larger than the value shown above.

Title: PHT032 Observations of Hot Stars (Oral)

Authors and affiliation: M. Runacres Astrofysisch Instituut, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussel, Belgium and R. Blomme Royal Observatory of Belgium, Ringlaan 3, B-1180 Brussel, Belgium


We study density inhomogeneities ("clumps") in the stellar winds of hot stars. The main problem with ISOPHOT observations of hot stars is their weak infrared flux, compared to the strong cirrus background. In order to be able to extract reliable values for the stellar fluxes, we have chosen to use PHT032 to take oversampled maps from a region around the star. We present first versions of these maps for a number of stars. In order to enhance the S/N of our observations, we attempted to save some of the data that are discarded in the standard PIA processing. We found that, in some cases, the first and the last readout of a ramp consisting of four readouts can be used. We have also experimented with deconvolution algorithms (such as the two-channel method of Lucy and Hook) to extract the stellar fluxes.

Title: PHT-S Observations of Seyfert Galaxies: Improved Data Reduction Techniques (Oral)

Authors and affiliation: B. Schulz, J. Clavel, B. Altieri, P. Barr, P. Claes, A.M. Heras, K. Leech, L. Metcalfe, A. Salama, G. Tagliaferri all ISO-SOC, Astrophysics Div., ESA


The evaluation of chopped measurements between 2.5 and 12 mu with PHT-S of faint Seyfert Galaxies, proposed by Clavel et al., are discussed. Major problems with these faint sources in the view of basic signal derivation are shown. A new data reduction technique is presented and compared with standard procedures already implemented in PIA. The objective was to minimise additional noise coming mainly from high energy particle hits in orbit, without loosing too much of the total integration time. Optimal processing parameters were determined. Accordingly processed preliminary results for the ten faintest objects of a total of about 30 observed so far are presented.

Title: Preliminary results of the ISOCAM deep survey for primeval galaxies (Oral)

Authors and affiliation: Yoshiaki Taniguchi et al. Tohoku Univ.


In order to search for reddened high-z galaxies, we have made a 6.7 micron deep survey with ISOCAM. The total integration time was 12 hours for one particular field in the Lockman HI hole. We report the current status of our project.

Title: ISOCAM Transients, Gain Drifts, and Sky Modelling at IPAC (Oral)

Authors and affiliation: D. Van Buren, M. Kong, J. Li, K. Ganga, R. Hurt (IPAC)


ISOCAM work at IPAC is directed toward obtaining accurate representations of the sky brightness distribution from the delivered data. Transient removal is essential for fields with structure. Our approach is to apply a physical model for the array's photocurrent under conditions of varying illumination to recover the incident flux history. This method works remarkably well - for many datasets, where collective effects are unimportant, fits to the data are within the noise. Of interest for deep experiments, we find that the ISOCAM-LW array has less noise during a transient than when "stabilized". Gain drifts can be very strong in some datasets, for example in the HDF. When the field is "blank", filtering in the time domain is valid to remove these baseline drifts. Substantial improvements in sensitivity result over the published maps. We have implemented a modelling approach for dealing with raster data, whereby the brightness of a sky pixel is fit via a geometric model to a dataset. This approach avoids the error cascade of the usual data unfolding approach where weighted sums are made of seaparte images to compose a mosaic. We find that for reduntant enough datasets the improvement in noise is up to a factor of a few.

Title: Spectral Energy Distributions of High-redshift Quasars (Oral)

Authors and affiliation: B.J. Wilkes, K.K.McLeod, M.S. Elvis, J.C. McDowell (SAO) C. Lonsdale (IPAC), C. Impey (U of A), M. Malkan (UCLA)


Over the past 10 years studies of the spectral energy distributions of quasars have become possible and our understanding of the energy generation mechanisms at work has greatly increased. However a key area in which little advance has been made is the far-infrared (IR) where data exists only for the lowest redshift and reddest quasars and over a limited range in wavelength. With ISO we are able, for the first time, to study the far-IR emission of a representative sample of quasars and over a wider energy range. Our program is obtaining photometry with ISOPHOT in eight broad bands between 5 and 200 microns for ~50 quasars and active galaxies having a wide variety of properties. Our sample includes subsets which are X-ray, optically and IR selected, high and low redshift. Our initial aim is to delineate the far-IR continuum in order to determine the peak wavelength and long wavelength turnover, measure the luminosity and to address the fundamental question of the relative importance of thermal and non-thermal emission in the different types of quasars. We will present preliminary results including detection of a high redshift (z>4) quasar.