Showing papers by "Dietrich Lemke published in 1998"

A Deep VLA survey at 20cm of the ISO ELAIS survey regions

Abstract: We have used the Very Large Array(VLA) in C configuration to carry out a sensitive 20cm radio survey of regions of sky that have been surveyed in the Far Infra-Red over the wavelength range 5-200 microns with ISO as part of the European Large Area ISO Survey(ELAIS). As usual in surveys based on a relatively small number of overlapping VLA pointings the flux limit varies over the area surveyed. The survey has a flux limit that varies from a 5$\sigma$ limit of 0.135mJy over an area of 0.12deg$^2$ to a 5$\sigma$ limit of 1.15mJy or better over the whole region covered of 4.22 deg$^2$. In this paper we present the radio catalogue of 867 sources. These regions of sky have previously been surveyed to shallow flux limits at 20cm with the VLA as part of the VLA D configuration NVSS(FWHM=45 arcsec) and VLA B configuration FIRST(FWHM=5 arcsec) surveys. We have carried out a a detailed comparison of the reliability of our own survey and these two independent surveys in order to assess the reliability and completeness of each survey.

On the Far-Infrared Emission of Quasars*

Abstract: Infrared spectral energy distributions between 4.8 and 200 μm are presented for a subsample of 10 quasars and radio galaxies from the European Central Quasar Programme observed with the Infrared Space Observatory. For three of the sources, this represents the first far-infrared detection. The spectral energy distributions (SEDs) reveal signatures of thermal dust as well as synchrotron emission. In most cases, one of the two components is so dominant that the other remains hidden. The SEDs of the radio-quiet and steep-spectrum quasars show a bump around 60 μm and a decline longward of 100 μm—strong evidence for thermal emission. It can be described as a superposition of several modified blackbodies, showing the broad variety of temperatures from hot (≈ 600 K) to cool (≈ 30 K) dust present in these objects. The infrared emission of the flat-spectrum radio quasars is in smooth continuation of the radio spectrum, supporting the interpretation as synchrotron emission. For one of these sources (3C 279), a bump is prying above the synchrotron spectrum, and we interpret it as thermal emission. For comparison within the framework of unified schemes, the radio galaxies Cyg A (3C 405) and 3C 20 are observed. While 3C 20 has not been detected, Cyg A reveals an infrared spectrum surprisingly similar to that of 3C 48 and the radio-quiet quasars, which strongly supports the interpretation of the radio galaxy Cyg A as a hidden quasar.

Far-infrared emission of intracluster dust in the Coma galaxy cluster.

Abstract: The ISOPHOT C200 camera aboard ISO has been used to observe the extended far infrared (FIR) emission from the Coma cluster of galaxies. Two scans with 48 0 length across the cluster, each at 120m and 185m, were obtained at cross- ing position angles. The proles of the surface brightness ratio I120m=I185m along the two scans are quite similar in show- ing an enhanced 120 m emission within the central region of 10 0 (0.4 Mpc) diameter. This flux excess is interpreted as thermal emission from intracluster dust with a temperature slightly higher than the galactic foreground cirrus. A conserva- tive value for the excess surface brightness at 120 mi s0.1 MJy/sr, corresponding to a total net flux of 0.7 Jy. Depend- ing on the dust opacity and temperature, a total dust mass of 6:210 7 M < MD < 1:610 9 M is inferred. The detected excess emission represents the rst direct evidence from FIR observation for intracluster dust in a galaxy cluster. Since dust is destroyed effectively by the hot intracluster medium, the dust detected may result from galaxy stripping during the ongoing merging process in Coma. FIR emission from intracluster dust thusmightbeusedasatooltosearchfornon-equilibriumgalaxy clusters.

ISOPHOT far-infrared serendipity sky survey

Abstract: The ISOPHOT Serendipity Survey utilizes the slew time between ISO's pointed observations with strip scanning measurements of the sky in the far-IR at 170 micrometers . The slews contain information about two fundamentally different types of objects, namely unresolved galactic and extragalactic far-IR sources as well as extended regions of galactic cirrus emission. Since the structure of the obtained data is almost unique, the development of dedicated software to extract astrophysically interesting parameters for the crossed sources is mandatory. Data analysis is currently in its early stages and concentrates on the detection of point sources. First results from an investigation of a high galactic latitude field near the North Galactic Pole indicate that the detection completeness with respect to previously known IRAS sources will be almost 100 percent for sources with f(subscript 100micrometers > 2 Jy, dropping below approximately equals 50 percent for f(subscript 100micrometers < 1.5 Jy. Nevertheless, even faint sources down to a level of f(subscript 170micrometers approximately equals 1 Jy can be detected. Since the majority of the detected point sources are galaxies, the Serendipity Survey will result in a large database of approximately equals 2000 galaxies.

Infrared straylight measurements of the ISO telescope

Abstract: Measurements were performed to verify the straylight suppression in the IR Space Observatory telescope using the ISOPHOT instrument. These test comprised the near-field straylight by bright stars and planets as well as the far- field straylight by the Sun, the Earth, and the Moon. No significant straylight above the specifications reflecting the astronomical needs for low surface brightness absolute sky measurements could be detected at 25 and 170 micrometers . In some cases comparison to preflight straylight simultaneous were possible. The consistency of the predictions from the models with the measurement results confirms the reasonable assumptions made for the simulations. This will allow to further optimize the telescope design for future low background IR space telescopes.

Detection of widely distributed UIR band emission in the disk of NGC 891

Abstract: The spectrum of the unidentified infrared (UIR) emission bands between 5.9 and 11.7 [micro]m has been observed for the first time in the disk of an external galaxy. We have used the low-resolution spectrometer of the ISOPHOT instrument aboard ISO. The UIR bands at 6.2, 7.7 and 11.3 [micro]m have absolute intensities which are similar to the values observed for the diffuse emission of our own Galaxy. The UIR bands between 5.9 and 11.7 [micro]m contribute ~9% of the total IR radiation of NGC 891. The intensity ratios and band widths in the NGC 891 disk emissions are similar to the diffuse emission of the Milky Way, pointing to a common carrier for the UIR bands in the two galaxies. However, there are some notable variations of the band ratios along the major axis of the galaxy.

Cold dust in the Andromeda Galaxy mapped by ISO

Abstract: A complete 175m map of the Andromeda galaxy (M31) at 1: 3 resolution shows the distribution of cold dust. It is dominated by a ring at 10 kpc radius supplemented by a faint outer one at 14 kpc. No clear spiral pattern is recognis- able. The azimuthally averaged radial brightness profile is rather flat within the 10 kpc ring and decreases exponentially outside thereof, discernible down to a brightness of 0.07 MJy/sr at a distance of 22 kpc. Since the ring comprises a large reservoir for star formation, as an evolutionary conjecture M31 might be in a transition phase changing its classical optical Sb type spiral morphology towards that of a ringed galaxy. The bulk of the dust has a temperature of only 16 K, con- siderably colder than the 21-22 K previously inferred from the IRAS data and also colder than the 19 K found for the Milky Way. The cold dust is accompanied by warm dust, formally described by a component at about 45 K. At the common res- olution of 2: 5 the triplet 60/100/175 m flux ratio varies only little across the rings as well as the disk, thus everywhere in M31 at least two dust components are required to fit the far-infrared spectral energy distribution. This provides a direct evidence in M31 for the existence of two dust populations - small and large grains - similar to what had been found in the Milky Way. For the cold dust component around 16 K we can now estimate the corresponding mass from its emission yielding 310 7 M, a dust mass about a factor of ten higher than in- ferred from the IRAS 60/100m data alone. The new cold dust mass - if evenly distributed in the plane of the galaxy - would be sufficient to make the disk of M31 moderately opaque in the optical (face-on: 0.1 M pc 2 corresponding to V 0.5).

Detection of UIR bands in an isolated local interstellar cirrus cloud

Abstract: The unidentied infrared (UIR) emission bands at 7.7 and 11.3 m have been detected in the emission of an iso- lated cirrus cloud externally heated by the typical interstellar radiation eld (ISRF) of the solar neighbourhood. For the ob- servations we used ISOPHOT, the photometer aboard ISO. The detected UIR bands have absolute intensities 1/1000th of the values typically observed in planetary and reflection nebulae. The intensity ratio 11.3 to 7.7 m is at the higher end of the range observed for reflection nebulae, planetaries, HII regions, or for the diffuse emission of the inner Galaxy. An enhanced emission level is observed also in the band s6-9 m and 12 -1 4m, suggesting the presence of the 6.2, 8.6 and 12.7 m UIR bands. At 10 and 16 m continuum emission has been de- tectedwhichmustbeduetoverysmallgrains.Theobservations presented give further evidence that the UIR features seem to be ubiquitous throughout the galaxy. This is in support of the PAHs as carriers of the features and, moreover, as key agents in transforming the stellar UV into infrared radiation.

ASTROPHYSICS Small-scale structures in the far-infrared background ?

Abstract: Four elds with areas ranging from 80 to 2000 arcmin 2 have been mapped with the photometer on board of the Infrared Space Observatory (ISO) at 90 and around 180m in regions of bright and faint cirrus. We examined the spatial characteristics of the infrared background emission with high spatial resolution and found that the fluctuations in the back- ground emission limit the detection sensitivity of ISOPHOT for most of our observations. At 90m the power law relation between the power in the fluctuations and the spatial frequen- cies established from IRAS data could be extended to twice as high spatial frequencies. At 180m the small-scale fluctua- tions were studied for the rst time by a cold space telescope with arcminute-resolution. A similar power law and spectral in- dex down to spatial scales of 3 0 as for the 90m component is found. For cirrus clouds the spatial frequency spectrum in the far-infrared has a similar shape as that derived from 21cm line observationsoftheinterstellarneutralhydrogen.Infaintregions the fluctuations are caused presumably by randomly distributed extragalactic sources. Future 3m class space telescopes survey- ing the sky around 200m will not be hampered by cirrus over most of the sphere.

The molecular cloud core M 17-North: ISO spectroscopy and IR/mm continuum mapping ?

Abstract: We present the first complete infrared spectrum of a molecular cloud core covering the wavelength region from 2.4 up to 200 m together with a map at 1.3 mm wavelength and near-infrared (NIR) images. The core is located in the north- ern part of M 17 and shows strong evidence for on-going star formation. These data are the first step towards a complete char- acterization of M 17-North. The spectrum has been obtained with the Infrared Space Observatory (ISO) using the short- and long-wavelength spec- trometers (SWS/LWS) with a resolution from 150 to 300. The spectrum of the core displays the unidentified infrared bands (UIBs). The continuum is rising rapidly for wavelengths larger than 15 m which is typical for objects with stronger UV radia- tion fields. This continuum is probably produced by the emission from very small grains (VSGs) heated transiently. Many low-excitation fine structure lines were detected which are typical for the emission from an Hii region. They are produced by an electron gas with a density and temperature of about 100 cm 3 and 5000 K, respectively. The mapping of the continuum radiation at 1.3 mm revealed the presence of a compact cloud core, whereas NIR imaging led to the detection of embedded IR objects. The observed spec- tral energy distribution (SED) is used to model the cloud core emission with radiative transfer (RT) calculations including the emission from VSGs. This calculation shows that the cloud core is mainly heated by an outer radiation field but needs an addi- tional inner heating source with a luminosity of about 8000 L to explain the measurements.

Small-scale structures in the far-infrared background

Abstract: Four fields with areas ranging from 80 to 2000 arcmin(2) have been mapped with the photometer on board of the Infrared Space Observatory (ISO) at 90 and around 180mu m in regions of bright and faint cirrus We examined the spatial characteristics of the infrared background emission with high spatial resolution and found that the fluctuations in the background emission limit the detection sensitivity of ISOPHOT for most of our observations At 90mu m the power law relation between the power in the fluctuations and the spatial frequencies established from IRAS data could be extended to twice as high spatial frequencies At 180mu m the small-scale fluctuations were studied for the first time by a cold space telescope with arcminute-resolution A similar power law and spectral index down to spatial scales of 3arcmin as for the 90mu m component is found For cirrus clouds the spatial frequency spectrum in the far-infrared has a similar shape as that derived from 21cm line observations of the interstellar neutral hydrogen In faint regions the fluctuations are caused presumably by randomly distributed extragalactic sources Future 3m class space telescopes surveying the sky around 200mu m will not be hampered by cirrus over most of the sphere Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA

The ISOPHOT far-infrared serendipity north ecliptic pole minisurvey

Abstract: The ISOPHOT Serendipity Survey fills the otherwise unused slew time between ISO’s fine pointings with measurements in an unexplored wavelength regime near 200 μm. In order to test point source extraction software, the completeness of the detected objects as well as the astrophysical content we investigate a 100ut field near the North ecliptic pole, dubbed ISOPHOT Serendipity Minisurvey field. A total of 21 IRAS point sources were detected on the Serendipity slews crossing the field. 19 of these objects are galaxies, one is a planetary nebula and one is an empty field without a bright optical counterpart. The detection completeness is better than 90% for IRAS sources brighter than 2 Jy at 100 μm and better than 80% for sources brighter than 1.5 Jy. The source detection frequency is about 1 per 40 slew length, in agreement with previous estimations based on galaxy number counts. After the end of the ISO mission, about 4000 point sources are expected to be found in the Serendipity slews.

Far-infrared ISOPHOT observations and the energy balance of a quiescent globule ?

Abstract: We have observed a quiescent small globule, the Thumbprint Nebula, with the ISOPHOT far-infrared camera at 100 and 200m. The observed emission is optically thin thermal emission from dust at a temperature of 14-16 K. The energy budget of the cloud is studied by considering the energy input (interstellar radiation field, ISRF), and outputs (scattered and emitted radiation). It is found that the ISRF is sufficient to be the only heating source of dust in the cloud. We have derived val- ues of absorption cross sections of dust at 100 and 200m, and found them to be in good agreement with current dust models.

Search for cool circumstellar matter in the Ursae Majoris group with ISO

Abstract: We observed the mid- and far-infrared spectral en- ergy distributions of 9 A-type stars from the 300 Myrs old Ursae Majoris group using the ISO satellite and the UKIRT telescope. We found that only 1 out of the 9 stars shows clear signature of circumstellar dust, and we derived an upper limit of 0.05 Mmoon for the dust mass around the other stars. Our results suggest that the relatively high incidence of Vega-like disks observed among A-type field stars in the solar neighbourhood by IRAS cannot be extrapolated to the rest of the Milky Way. The Vega phenomenon appears to be the exception rather than the rule.

ISOPHOT: in-flight performance report

Abstract: The imaging photopolarimeter ISOPHOT on-board the European satellite ISO houses 144 background detectors of Si:Ga, Si:P, Ge:Ga and stressed Ge:Ga, all sampled by newly developed cold read-out electronics. There is large temporal radiation damage to most of these detectors on the daily passage through the earth's radiation belts. In addition the Ge:Ga detectors exhibit a continuous responsivity increase caused by the cosmic radiation far off the earth. Effective curing procedure shave been developed to heat out these effects. The in-flight sensitivities achieved are close to the pre-flight predictions for most channels. At 100-200 micrometers cirrus confusion is a serious limit for the detection of faint objects on large parts of the sky. The cold filter wheel carrying 56 optical elements, such as filters, apertures and polarizers, as well as the focal plane chopper, operate with high precision and very low power consumption. Due to an effective cold internal baffle system the measured near-field straylight was close to the pre- flight theoretical prediction based on APART simulations. THe sun and moon straylight at 25 and 175 micrometers was measured during several solar eclipses. Drift and transients of the detectors, non-linearities of the preamplifiers, ionizing radiation effects and a complex optical path make the photometric calibration of this instrument challenging. Because most of these effects are reproducible, a calibration accuracy of < 30 percent is already available for most photometric modes. Examples of observations, including the 175 micrometers Serendipitous Sky Survey, will highlight the capabilities of the instrument.

Observations with Isophot

Abstract: While all channels of the instrument (Lemke et al. 1996) are fully operational in the 21st month of the mission, some have turned out to be particularly productive: (1) far infrared mapping in the 200 μm range and (2) spectrophotometry in the middle infrared. The detection sensitivity of these modes is close to the preflight expectation. The photometric calibration of the instrument is a demanding task. Transient and memory effects of the low background detectors, responsivity drifts and spikes caused by the cosmic radiation as well as nonlinearities due to the preamps and the complex optical subsystems require corrections. Fortunately almost all of these effects are reproducable and correction algorithms are under development. While spectrophotometric (Klaas et al. 1997) and staring observations are already calibrated to better than ±20. 30% in the pipeline data products, similar values will be achieved for all observing modes in the near future.

The european large area iso survey - isophot results using the mpia-pipeline

Abstract: The European Large Area ISO Survey (ELAIS) will provide Infrared observations of 4 regions in the sky with ISO. Around 2000 Infrared sources have been detected at 7 and 15 microns (with ISOCAM), 90 and 175 microns (with ISOPHOT)) over 13 square degrees of the sky. We present the source extraction pipeline of the 90 microns ISOPHOT observations, describe and discuss the results obtained and derive the limits of the ELAIS observational strategy.

FIRSA: the demonstrator array of the FIR camera for the photoconductor instrument PACS on ESA's FIRST satellite

Abstract: PACS covers the wavelength range 80-210 micrometers in spectrometric and photometric imaging modes. The long wavelength camera is a 16 X 25 pixel array of stressed Ge:Ga detectors. In order to demonstrate the feasibility of such a large array, one of the 25 linear arrays was manufactured. It consists of 16 elements of 1.5 mm3 each separated by ceramic plungers and stressed by one single mechanism. As preamplifier a dedicated CMOS circuit was developed, based on similar circuits successfully operating in ISO's photometer. In particular, it was intended to increase the gain of the CRE in order to minimize the debiasing effects on the low bias operated detectors. Two complete linear demonstrator arrays were manufactured and independently tested under various low background conditions in a 1.7 K environment at MPIA and MPE. The feasibility of the concept chosen was demonstrated in several functional tests. Valuable experience was gained to guide the development of the next generation of CREs and arrays.

Far-Infrared Photometry of Circumstellar Matter Around Intermediate Mass Stars

Abstract: Many intermediate mass stars show signatures of circumstellar material. The young pre-main sequence Herbig Ae/Be stars often show flat or rising spectral energy distributions (SEDs) in the far-infrared, attributed to thermal emission of heated circumstellar dust, the remnant of star formation. A significant fraction of the much older main-sequence B and A-type stars also shows excess emission at λ ≥ 25µm (the so-called Vega-phenomenon, Backman and Paresce 1993), interpreted in terms of circumstellar disks maintained by destruction of asteroids and comets. The evolution from the circumstellar disks/envelopes of Herbig Ae/Be stars to Vega-like disks is, however, not well documented by observations (for an attempt using submm observations see Zuckerman and Becklin 1993). The evolutionary history, however, provides information on the lifetime of accretion disks around intermediate mass stars, and helps to clarify the role of these disks in stellar evolution, as well as defines the timescale for planet formation.

The European Large Area ISO Survey: Elais

Abstract: I describe a project to survey ∼ 13 square degrees of the sky at 15 μ m and 90 μ m with the Infrared Space Observatory (ISO). The European Large Area ISO Survey (ELAIS) is a collaboration involving 19 European institutes (in addition to the authors and others at their institutes the following people and others their institutes are involved I. Gonzalez-Serrano, E. Kontizas, K. Mandolesi, J. Masegosa, K. Mattila, H. Norgaard-Nielsen, I. Perez-Fournon, M. Ward) and is the largest open time project being undertaken by ISO. We expect to detect at least 1000 extra-galactic objects and a similar number of Galactic sources.