Showing papers by "Dietrich Lemke published in 2001"

Infrared to millimetre photometry of ultra-luminous IR galaxies: new evidence favouring a 3-stage dust model

Abstract: Infrared to millimetre spectral energy distributions have been obtained for 41 bright ultra-luminous infrared galaxies. The observations were carried out with ISOPHOT between 10 and 200 micron and supplemented for 16 sources with SCUBA at 450 and 850 micron and with SEST at 1.3 mm. In addition, seven sources were observed at 1.2 and 2.2 $\mu$m with the 2.2 m telescope on Calar Alto. These new SEDs represent the most complete set of infrared photometric templates obtained so far on ULIRGs in the local universe.

Infrared to millimetre photometry of ultra-luminous ir galaxies: new evidence favouring a 3-stage dust model

Abstract: Infrared to millimetre spectral energy distributions (SEDs) have been obtained for 41 bright ultra- luminous infrared galaxies (ULIRGs). The observations were carried out with ISOPHOT between 10 and 200 m and supplemented for 16 sources with JCMT/SCUBA at 450 and 850 m and with SEST at 1.3 mm. In addition, seven sources were observed at 1.2 and 2.2 m with the 2.2 m telescope on Calar Alto. These new SEDs represent the most complete set of infrared photometric templates obtained so far on ULIRGs in the local universe. The SEDs peak at 60{100 m and show often a quite shallow Rayleigh-Jeans tail. Fits with one single modied blackbody yield a high FIR opacity and small dust emissivity exponent T >30 K) to cold (30 K >T >10 K) temperatures. This provides evidence for two dust stages, the cool starburst dominated one and the cold cirrus-like one. The third stage with several hundred Kelvin warm dust is identied in the AGN dominated ULIRGs, showing up as a NIR-MIR power- law flux increase. While AGNs and SBs appear indistinguishable at FIR and submm wavelengths, they dier in the NIR-MIR. This suggests that the cool FIR emitting dust is not related to the AGN, and that the AGN only powers the warm and hot dust. In comparison with optical and MIR spectroscopy, a criterion based on the SED shapes and the NIR colours is established to reveal AGNs among ULIRGs. Also the possibility of recognising evolutionary trends among the ULIRGs via the relative amounts of cold, cool and warm dust components is investigated.

FIRBACK: III. Catalog, source counts, and cosmological implications of the 170 mu m ISO

Abstract: The FIRBACK (Far Infrared BACKground) survey is one of the deepest imaging surveys carried out at 170 μm with ISOPHOT onboard ISO, and is aimed at the study of the structure of the Cosmic Far Infrared Background. This paper provides the analysis of resolved sources. After a validated process of data reduction and calibration, we perform intensive simulations to optimize the source extraction, measure the confusion noise (σ_c = 45 mJy), and give the photometric and astrometric accuracies. 196 galaxies with flux S > 3σ_c are detected in the area of 3.89 square degrees. Counts of sources with flux S > 4σ_c present a steep slope of 3.3 ± 0.6 on a differential "log N-log S"plot between 180 and 500 mJy. As a consequence, the confusion level is high and will impact dramatically on future IR deep surveys. This strong evolution, compared with a slope of 2.5 from Euclidian geometry, is in line with models implying a strongly evolving Luminous Infrared Galaxy population. The resolved sources account for less than 10% of the Cosmic Infrared Background at 170 μm, which is expected to be resolved into sources in the 1 to 10 mJy range.

FIRBACK: III. Catalog, Source counts, and cosmological implications of the 170 micron ISO Deep survey

Abstract: The FIRBACK (Far Infrared BACKground) survey is one of the deepest imaging surveys carried out at 170 microns with ISOPHOT onboard ISO, and is aimed at the study of the structure of the Cosmic Far Infrared Background. This paper provides the analysis of resolved sources. After a validated process of data reduction and calibration, we perform intensive simulations to optimize the source extraction, measure the confusion noise (sigma_c = 45 mJy), and give the photometric and astrometric accuracies. 196 galaxies with flux S > 3 sigma_c are detected in the area of 3.89 square degrees. Counts of sources with flux S > 4 sigma_c present a steep slope of 3.3 +/- 0.6 on a differential "logN-logS" plot between 180 and 500 mJy. As a consequence, the confusion level is high and will impact dramatically on future IR deep surveys. This strong evolution, compared with a slope of 2.5 from Euclidian geometry, is in line with models implying a strongly evolving Luminous Infrared Galaxy population. The resolved sources account for less than 10% of the Cosmic Infrared Background at 170 microns, which is expected to be resolved into sources in the 1 to 10 mJy range.

Broadband infrared photometry of comet Hale-Bopp with ISOPHOT ?

Abstract: Comet Hale-Bopp was observed ve times with ISOPHOT, the photometer on board ESA's Infrared Space Observatory (ISO) between 4.6 and 2.8 AU. Each time, broadband photometry was performed using 4 dierent detectors, 5 apertures and 10 lters covering the range between 3.6 and 170 m. Background ob- servations were performed with identical instrument settings at the same positions on the sky several days after the comet observations. The observation strategy and the data reduction steps are described in some detail, including the techniques to correct for variable detector responsivity. The resulting inband power values of the Hale-Bopp observations and their uncertainties are given. The mean uncertainty is 25%. The nal fluxes were computed, taking into account the zodiacal background, possible oset of the comet's position from the center of the aperture, the brightness distribution within the coma, and the spectral energy distribution of the comet's emission. Strong thermal emission from a broad size distribution of dust particles was detected in all of the data sets, even at r =4 :6{4:9 AU pre-perihelion and 3.9 AU post-perihelion; the total thermal energy varied as r 3 . The 7.3{12.8 m color temperature was1.5 times the blackbody temperature, higher than that observed in any other comet. Silicate features at 10 and 25 m were prominent in all 5 data sets, the largest heliocentric distances that silicate emission has been detected in a comet. The presence of crystalline water ice grains is suggested from the 60 m excess emission at 4.6{4.9 AU, consistent with the observed QOH if the icy grains were slightly warmer than an equilibrium blackbody. The average albedo of the dust is higher than that of comet P/Halley, but lower than other albedo measurements for Hale-Bopp nearer perihelion. There is no evidence for a component of cold, bright icy grains enhancing the scattered light at 4.6 AU. Simple models for a mixture of silicate and absorbing grains were t to the ISO spectra and photometry at 2.8 AU. The observed flux at >100 mr equires a size distribution in which most of the mass is concentrated in large particles. Dust production rates of order 1:5 10 5 kg s 1 at 2.8 AU and 3 10 4 kg s 1 at 4.6 AU have been found. They correspond to dust to gas mass ratios of 6 to 10.

Far-infrared mapping of the starburst galaxy NGC 253 with ISOPHOT ?

Abstract: A 180 m map and strip maps at 120 and 180 m were obtained for the edge-on starburst galaxy NGC 253 with ISOPHOT, the photometer on board the Infrared Space Observatory .W e compare these observa- tions with those obtained by IRAS at 60 m and 100 m and derive the far{infrared spectral energy distribution at dierent locations in the galaxy. There is evidence for the presence of cold dust (T 20 K) both in the nucleus and in the disk. Extended emission dominated by cold dust is detected up to15 0 (10 kpc) along the major and minor axis; its spatial distribution is similar to that seen in the IRAS and ROSAT PSPC images. The emission along the minor axis is probably related to large-scale outflows of gas (superwinds) which originate in the nuclear starburst and maybe to star formation in the halo. The radial dependence of the dust temperature along the major axis is found using a radiative transfer code: we show that the dust scale length in the disk is40% larger than that of stars.

Dust emission from 3C radio galaxies and quasars: New ISO observations favour the unified scheme

Abstract: In order to test the unied scheme for luminous radio galaxies and quasars we observed 10 galaxy/quasar pairs from the 3CR catalogue with ISOPHOT at infrared wavelengths between 5 and 180 m. Each pair was selected such that both the 178 MHz luminosity and the redshift match as close as possible between the radio galaxy and the quasar in order to minimize eects of cosmic evolution. 13 of the 20 sources were detected in at least one waveband. 12 sources show clear evidence of a thermal bump at FIR wavelength, while in the remaining 7 sources the upper limits are still compatible with the presence of luminous dust emission. In agreement with the predictions of the unied scheme, the quasars and galaxies in our sample cannot be distinguished by their observed mid- and far-infrared properties. This is in contrast to the ndings on the basis of the IRAS scans which indicated that radio galaxies radiate signicantly less mid- to far-infrared emission than quasars. However, the IRAS samples are dominated by low-redshift sources ( z 0:8). At lower redshifts ( z< 0:5), however, some of the lobe-dominated FRII radio galaxies contain active nuclei which emit less UV-optical continuum than the quasars of similar radio power. As this division is mainly a function of redshift and less one of absolute radio power, we suggest that it is caused by the evolution of the nuclear fueling rate with cosmic epoch. In order to quantify the deviation from the purely aspect-dependent unied scheme at low redshifts a larger fraction of 3C radio galaxies has to be observed at mid- to far-infrared wavelengths with sensitivities which suce to yield secure detections rather than upper limits.

Dust emission from 3C radio galaxies and quasars: New ISO observations favour the unified scheme

Abstract: In order to test the unified scheme for luminous radio galaxies and quasars we observed 10 galaxy/quasar pairs from the 3CR catalogue with ISOPHOT at infrared wavelengths between 5 and 180 micron. Each pair was selected such that both the 178 MHz luminosity and the redshift match as close as possible between the radio galaxy and the quasar in order to minimize effects of cosmic evolution. 13 of the 20 sources were detected in at least one waveband. 12 sources show clear evidence of a thermal bump at FIR wavelength, while in the remaining 7 sources the upper limits are still compatible with the presence of luminous dust emission. In agreement with the predictions of the unified scheme, the quasars and galaxies in our sample cannot be distinguished by their observed mid- and far-infrared properties. This is in contrast to the IRAS results which indicated that radio galaxies radiate significantly less mid- to far-infrared emission than quasars. However, the IRAS samples are dominated by low-redshift sources (z 0.8). At lower redshifts (z < 0.5), however, some of the FRII radio galaxies contain active nuclei which emit less UV-optical continuum than the quasars of similar radio power. (abrigded)

Sky confusion noise in the far-infrared: Cirrus, galaxies and the cosmic far{infrared background ?

Abstract: We examined the sky confusion noise in 40 sky regions by analysing 175 far-infrared (90{200 m) maps obtained with ISOPHOT, the photometer on-board the Infrared Space Observatory. For cirrus elds with hBi > 5M Jy sr 1 the formula based on IRAS data (Helou & Beichman 1990) predicts confusion noise values within a factor of 2 of our measurements. The dependence of the sky confusion noise on the surface brightness was determined for the wavelength range 90 200 m. We veried that the confusion noise scales as N/hBi 1:5 , independent of the wavelength and conrmed N/ 2:5 for 100 m. The scaling of the noise value at dierent separations between target and reference positions was investigated for the rst time, providing a practical formula. Since our results conrm the applicability of the Helou & Beichman (1990) formula, the cirrus confusion noise predictions made for future space missions with telescopes of a similar size can be trusted. At 90 and 170 ma noise term with a Poissonian spatial distribution was detected in the faintest elds (hBi3 5M Jy sr 1 ), which we interpret as fluctuations in the Cosmic Far-Infrared Background (CFIRB). Applying ratios of the fluctuation amplitude to the absolute level of 10% and 7% at 90 and 170 m, respectively, as supported by model calculations, we achieved a new simultaneous determination of the fluctuation amplitudes and the surface brightness of the CFIRB. The fluctuation amplitudes are 7 2m Jy and 15 4 mJy at 90 and 170 m, respectively. We obtained a CFIRB surface brightness of B0 =0 :8 0: 2M Jy sr 1 (I =1 4 3n W m 2 sr 1 )a t 170m and an upper limit of 1.1 MJy sr 1 (I =3 7 nW m 2 sr 1 )a t 90m.

Far-Infrared Emission from Intracluster Dust in Abell Clusters

Abstract: The ISOPHOT instrument aboard ISO has been used to observe extended FIR emission of six Abell clusters. The raw profiles of the I_(120 um) / I_(180 um) surface brightness ratio including zodiacal light show a bump towards Abell 1656 (Coma), dips towards Abell 262 and Abell 2670, and are without clear structure towards Abell 400, Abell 496, and Abell 4038. After subtraction of the zodiacal light, the bump towards Abell 1656 is still present, while the dips towards Abell 262 and Abell 2670 are no longer noticable. This indicates a localized excess of emitting material outside the Galaxy towards Abell 1656, while the behavior in Abell 262 and Abell 2670 can be reconciled with galactic cirrus structures localized on the line-of-sight to these clusters. The excess towards Abell 1656 (Coma) is interpreted as thermal emission from intracluster dust distributed in the hot X-ray emitting intracluster medium. The absence of any signature for intracluster dust in five clusters and the rather low inferred dust mass in Abell 1656 indicates that intracluster dust is likely not responsible for the excess X-ray absorption seen in cooling flow clusters. These observations thereby represent a further unsuccessful attempt in detecting the presumed final stage of the cooling flow material, in accord with quite a number of previous studies in other wavelengths regions. Finally, the observed dimming of the high-redshift supernovae is unlikely be attributable to extinction caused by dust in the intracluster or even a presumed intercluster medium.

A far infrared view of low mass star formation in the Cederblad 110 nebula of Chamaeleon I

Abstract: The Cederblad 110 reflection nebula contains several young stellar objects previously discovered by IRAS and sub-mm observations. This cluster was revisited with ISO’s FIR cameras and mapped with higher spatial resolution. All sources were also mapped for the first time near the maximum of their spectral energy distribution at 200 μm. In addition, two new FIR-sources were discovered. The new data enabled parameters of the young objects to be determined, such as their luminosity, temperature and mass of the circumstellar dust. These parameters were related to the YSO classes of the various objects ranging from the pure protostar Class O to Class III. Cederblad 110 can be viewed as a compact volume of active low mass star formation in a dense ridge of molecular gas of the Chamaeleon I cloud detected e.g. in HNC and CO lines. The star formation efficiency in the 0.001 pc cluster volume is high; about 20% of the gas is now bound into stars.

Dense gas and cold dust in the dark core B217

Abstract: The Barnard object B217 was observed in the infrared and radio region. The 170 m continuum was detected with ISOPHOT, the ammonia 1.3 cm radio lines with the Eelsberg 100 m-telescope. Mapping B217SW in (J;K )=( 1; 1) and (2; 2) inversion lines revealed the temperature and density distribution of the gas and made it possible to investigate the dynamical state of this dense core inside B217. The ISOPHOT Serendipity Survey (ISOSS) detected the cold dust emission of B217 in all of 3 slews crossing the region. Combining ISOSS with IRAS data, we derive the core parameters of the dust from FIR emission and compare them with the NH3 data, which sample the densest region of the core. This study shows the power of combining ISOSS 170 mw ith IRAS/HIRES data in order to study the dust characteristics in nearby star forming regions on small spatial scales. The (170m/100m) dust colour temperature is 11 K{12 K in the dense cores and 12 K{14 K in the other regions of B217. The low dust temperatures cannot be explained by attenuation of the interstellar radiation eld alone and may reflect a change in the optical properties of the dust as compared to diuse clouds. In B217SW, molecular depletion through freeze-out onto grains is suggested by the comparison of our FIR and NH3 data with previous C 18 O observations. On the basis of our ammonia data investigation, we nd in B217SW dense gas with kinetic temperatures between 9 K and 12 K, increasing outwards. Using near-infrared extinction and NH3 collisional excitation calculations, the fractional ammonia abundance (N(NH3)=N (H2)) is found to be 3{5 10 8 , and the comparison of gas and dust observations supports this range. Knowing the ammonia abundance, we calculate the thermal, turbulent and gravitational energies of the dense core, which appears to be close to hydrostatic equilibrium. Our results are compatible with B217SW being now on the verge of collapse or in an early collapse phase.

ISOPHOT - Photometric Calibration of Point Sources

Abstract: All observations by the aperture photometer (PHT-P) and the far-infrared (FIR) camera section (PHT-C) of ISOPHOT included reference measurements against stable internal fine calibration sources (FCS) to correct for temporal drifts in detector responsivities. The FCSs were absolutely calibrated in-orbit against stars, asteroids and planets, covering wavelengths from 3.2 to 240 micron. We present the calibration concept for point sources within a flux-range from 60 mJy up to 4500 Jy for staring and raster observations in standard configurations and discuss the requisite measurements and the uncertainties involved. In this process we correct for instrumental effects like nonlinearities, signal transients, time variable dark current, misalignments and diffraction effects. A set of formulae is developed that describes the calibration from signal-level to flux densities. The scatter of 10 to 20 % of the individual data points around the derived calibration relations is a measure of the consistency and typical accuracy of the calibration. The reproducibility over longer periods of time is better than 10 %. The calibration tables and algorithms have been implemented in the final versions of the software for offline processing and interactive analysis.

A cold focal plane chopper for Herschel-PACS - critical components and reliability

Abstract: A chopper acts as an optical switch within the entrance optics of the PACS instrument onboard the ESA Space Observatory HERSCHEL to discriminate the light of faint celestial sources from a large background flux, which is basically due to the thermal radiation of the only moderately cooled 3.5mtelescope (≈ 80K). This chopper primarily consists of a small electrically driven tilting mirror with a high position accuracy for the full range of elongations up to ±9◦ to be operated at 4K with a power dissipation of less than 4mW. At a chopping frequency of up to 10Hz in square wave modulation scheme a duty cycle of 80% is to be achieved. After a pre-development phase at MPIA, which resulted in an optimized and cold tested prototype, the industrial optimization and implementation of the PACS chopper started in 2000 in a cooperation with the company Zeiss (Oberkochen). We focus on the new design of the chopper and its critical components, including the recently developed double-stage flexural pivots as high reliable bearings of the chopping mirror axis. The monolithic CuBe2 layout has to resist vibration loads of up to 45g during the launch of the ARIANE 5 carrier and to guarantee for an accurate motion in a cryogenic environment during a lifetime of at least 3 years in space, which corresponds to 630 Mio cycles of the chopper. Other components like the cryomotor and the rotor will be considered with respect to the selection of optimal materials, the reliability of mechanical linkages and the compensation of thermal stresses within the whole multi-material chopper assembly. I. HERSCHEL SATELLITE In 2007 ESA will launch the HERSCHEL satellite (formerly known as FIRST) as another cornerstone mission of its ”Horizon 2000 long term programme” [1]. This multi-user device will be the biggest and most powerful infrared observatory of its time. With a wavelength coverage between 60 and 670μm it will be sensitive especially in the far-infrared and submillimeter region, thus exploring radiation in a very unknown range of the electromagnetic spectrum. Scientific objectives, which will be addressed by HERSCHEL, range from the exploration of the distant universe and the question how first stars and galaxies were born, across the formation of planetary systems up to the investigation of our own solar system. 3.5m primary mirror sun shield + collector cryostat + scientific instruments

Sky Confusion Noise in the Far-Infrared: Cirrus, Galaxies and the Cosmic Far-Infrared Background

Abstract: We examined the sky confusion noise in 40 sky regions by analysing 175 far-infrared (90--200 $\mu$m) maps obtained with ISOPHOT, the photometer on-board the Infrared Space Observatory. For cirrus fields with $\rm > 5$ MJysr$^{-1}$ the formula based on IRAS data (Helou & Beichman, \cite{Helou+Beichman_90}) predicts confusion noise values within a factor of 2 to our measurements. The dependence of the sky confusion noise on the surface brightness was determined for the wavelength range 90 $\le \lambda \le$ 200 $\mu$m. We verified that the confusion noise scales as N ~ ^{1.5}, independent of the wavelength and confirmed N ~ lambda^{2.5}$ for lambda >= 100$um. The scaling of the noise value at different separations between target and reference positions was investigated for the first time, providing a practical formula. Since our results confirm the applicability of the Helou & Beichman (1990) formula, the cirrus confusion noise predictions made for future space missions with telescopes of a similar size can be trusted. At 90 and 170um a noise term with a Poissonian spatial distribution was detected in the faintest fields ( <= 3-5 MJysr^{-1}), which we interpret as fluctuations in the Cosmic Far-Infrared Background (CFIRB). Applying ratios of the fluctuation amplitude to the absolute level of 10% and 7% at 90 and 170um, respectively, as supported by model calculations, we achieved a new simultaneous determination of the fluctuation amplitudes and the surface brightness of the CFIRB. The fluctuation amplitudes are 7(+/-)2 mJy and 15(+/-)4 mJy at 90 and 170um, respectively. We obtained a CFIRB surface brightness of B(0)=0.8(+/-)0.2 MJysr^{-1} (nuI_nu=14(+/-)3nWm^-2sr^-1) at 170um and an upper limit of 1.1 MJysr^{-1} (nuI_nu=37 nWm^-2sr^-1) at 90um.

Far-infrared mapping of the starburst galaxy NGC 253 with ISOPHOT

Abstract: A 180 micron map and strip maps at 120 and 180 microns were obtained for the edge-on starburst galaxy NGC 253 with ISOPHOT, the photometer on board the Infrared Space Observatory. We compare these observations with those obtained by IRAS at 60 micron and 100 micron and derive the far--infrared spectral energy distribution at different locations in the galaxy. There is evidence for the presence of cold dust (T < 20 K) both in the nucleus and in the disk. Extended emission dominated by cold dust is detected up to 15 arcmin (~ 10 kpc) along the major and minor axis; its spatial distribution is similar to that seen in the IRAS and ROSAT PSPC images. The emission along the minor axis is probably related to large-scale outflows of gas (superwinds) which originate in the nuclear starburst and maybe to star formation in the halo. The radial dependence of the dust temperature along the major axis is found using a radiative transfer code: we show that the dust scale length in the disk is ~ 40% larger than that of stars.

The ISOPHOT 170 Micron Serendipity Sky Survey : A Plea to FIRST

Abstract: The ISOPHOT Serendipity Survey utilized the slew time between ISO’s pointed observations with strip scanningmeasurements of the sky in the far-infrared (FIR) at 170µm. The integral 170µm fluxes for compact sources derived from the slews are put on an absolute flux level by usinga number of g alaxies as calibrator sources observed with ISOPHOT’s photometric mappingmode, supplemented by Serendipity Survey observations of two planets and two asteroids with available model fluxes. A first group of 115 well-observed sources with a high signalto-noise ratio in all four detector pixels havinga g alaxy association were extracted from the slew data with low (I100µm ≤ 15 MJy/sr) cirrus background. For all but a few galaxies, the 170µm fluxes are determined for the first time, which represents a significant increase in the number of galaxies with measured FIR fluxes beyond the IRAS 100µm limit. The large fraction of sources with a high F170µm/F100µm flux ratio indicates that a very cold (T < 20 K) dust component is present in many galaxies. The typical mass of the coldest dust component is MDust =1 0 7.5 ±0.5 M� , a factor 2 – 10 larger than that derived from IRAS fluxes alone. As a consequence, the gas-to-dust ratios are much closer to the canonical value for the Milky Way. A similar Serendipity Survey with FIRST has the prospects of deliveringFIR data with a much hig her angular resolution (PACS) or at longer wavelengths (SPIRE) than ISOPHOT, thereby providingeither crucial information for the identification of compact sources in confused regions or extending the spectral coverage for a large number of sources and findingrare classes of very cold FIR emitters.

Far Infrared Extragalactic Background Radiation: Source Counts with ISOPHOT

Abstract: As a part of the ISOPHOT CIRB (Cosmic Infrared Background Radiation) project we have searched for point-like sources in eight fields mapped at two or three wavelengths be- tween 90 m and 180m. Most of the 55 sources detected are suspected to be extragalactic and cannot be associated with pre- viously known objects. It is probable, also from the far-infrared (FIR) spectral energy distributions, that dust-enshrouded, dis- tant galaxies form a significant fraction of the sources. We present a tentative list of new extragalactic FIR-sources and discuss the uncertainties involved in the process of extract- ing point sources from the ISOPHOT maps. Based on the an- alyzed data we estimate the number density of extragalactic sources at wavelengths 90 m, 150 m and 180m and at flux density levels down to 100 mJy to be 110 5 sr 1 ,2 10 5 sr 1 , and 310 5 sr 1 , respectively. Strong galaxy evolution models are in best agreement with our results, although the number of detections exceeds most model predictions. No-evolution models can be rejected at a high confidence level. Comparison with COBE results indicates that the detected sources correspond to > 20% of the extragalactic background light at 90 m. At longer wavelengths the corresponding fraction is 10%. in the CIRB. Some central, but still largely open, astrophysical problems to be addressed through CIRB measurements include the formation and early evolution of galaxies, and the star for- mation history of the universe.