Showing papers by "Dietrich Lemke published in 2003"

The ISO view of Palomar-Green quasars

Abstract: Mining the ISO data archive we provide the complete ISO view of PG quasars containing 64 infrared spectral energy distributions between 5 and 200 mu m. About half of the sample was supplemented by MAMBO and SCUBA (sub-)millimeter data. Since the PG quasars were selected optically, the high infrared detection rate of more than 80% suggests that every quasar possesses luminous to hyper-luminous dust emission with dust masses comparable to Seyferts and ultra-luminous IR galaxies (ULIRGs). The gas to-dust mass ratio (of those sources where CO measurements are available in the literature) is consistent with the galactic value providing further evidence for the thermal nature of the IR emission of radio quiet quasars. The SEDs represent templates of unprecedented detail and sensitivity. We suggest that the diversity of the SEDs reflects largely the evolution of the dust distribution, and we propose a classification of the SED shapes as well as an evolutionary scheme in which this variety can be understood. During the evolution the surrounding dust redistributes, settling more and more into a torus/disk like configuration, while the SEDs show an initial FIR bump, then an increasing MIR emission and a steeper near- to mid-infrared slope, both of which finally also decrease. Regarding cosmic evolution, our hyper-luminous quasars in the "local" universe at z=l do not show the hyper-luminous (LFIR >? 10(exp 13) L(sub sun)) starburst activity inferred for z=4 quasars detected in several (sub-)millimeter surveys. In view of several caveats this difference should be established further, but it already suggests that in the early dense universe stronger merger events led to more powerful starbursts accompanying the quasar phenomenon, while at later cosmic epochs any coeval starbursts obviously do not reach that high power and are outshone by the AGN. Additional information is included in the original extended abstract.

The spiral galaxy M33 mapped in the FIR by ISOPHOT. A spatially resolved study of the warm and cold dust.

Abstract: The Sc galaxy M 33 has been mapped with ISOPHOT in the far-infrared, at 60, 100, and 170 µm. The spatial resolution of these FIR maps allows the separation of spiral arms and interarm regions and the isolation of a large number of star-forming regions. The spectral energy distribution in the FIR indicates a superposition of two components, a warm one originating from dust at ∼45 K, and a cold one, at ∼16 K. The warm component is concentrated towards the spiral arms and the star-forming regions, and is likely heated by the UV radiation from OB stars. The cold component is more smoothly distributed over the disk, and heated by the diffuse interstellar radiation. For the about 60 star-forming regions detected the Hα/FIR flux ratio increases significantly with the distance from the galaxy center, probably due to decreasing extinction. An anti-correlation of FHa/F60 with F170 suggests the intrinsic extinction to be related to the cold dust surface brightness according to AV /S 170 ∼ 0.03 mag MJy −1 sr. For the total galaxy the star formation rate (SFR) derived from the FIR is in agreement with that derived from the de-extincted Hα emission. For individual star-forming regions, a consistency between SFRs derived from the optical and from the FIR requires only a fraction of the UV radiation to be absorbed locally. The individual star-forming regions also show a local radio-FIR correlation. This local correlation is, however, due to quite different components than to those that lead to the well-known global radio-FIR correlation for entire galaxies.

The spiral galaxy M33 mapped in the FIR by ISOPHOT: A spatially resolved study of the warm and cold dust

Abstract: The Sc galaxy M33 has been mapped with ISOPHOT in the far-infrared, at 60, 100, and 170mue. The spatial resolution of these FIR maps allows the separation of spiral arms and interarm regions and the isolation of a large number of star-forming regions. The spectral energy distribution in the FIR indicates a superposition of two components, a warm one originating from dust at ~45K, and a cold one, at ~16K. The warm component is concentrated towards the spiral arms and the star-forming regions, and is likely heated by the UV radiation from OB stars. The cold component is more smoothly distributed over the disk, and heated by the diffuse interstellar radiation. For the about 60 star-forming regions detected the H-alpha/FIR flux ratio increases significantly with the distance from the galaxy center, probably due to decreasing extinction. An anti-correlation of F_Ha/F_60 with F_170 suggests the intrinsic extinction to be related to the cold dust surface brightness according to A_V/S_170~0.03mag/MJy*sr. For the total galaxy the star formation rate (SFR) derived from the FIR is in agreement with that derived from the de-extincted H-alpha emission. For individual star-forming regions, a consistency between SFRs derived from the optical and from the FIR requires only a fraction of the UV radiation to be absorbed locally. The individual star-forming regions also show a local radio-FIR correlation. This local correlation is, however, due to quite different components than to those that lead to the well-known global radio-FIR correlation for entire galaxies.

Unidentified infrared bands in the interstellar medium across the galaxy

Abstract: We present a set of 6–12 $\rm{\mu m}$ ISOPHOT-S spectra of the general interstellar medium of the Milky Way. This part of the spectrum is dominated by a series of strong, wide emission features commonly called the Unidentified Infrared Bands. The sampled area covers the inner Milky Way from l = -60°to +60° with a ten-degree step in longitude and nominal latitudes b = 0°, ± 1°. For each grid position the actual observed direction was selected from IRAS 100 $\rm{\mu m}$ maps to minimize contamination by point sources and molecular clouds. All spectra were found to display the same spectral features. Band ratios are independent of band strength and Galactic coordinates. A comparison of total observed flux in band features and IRAS 100 $\rm{\mu m}$ emission, a tracer for large interstellar dust grains, shows high correlation at large as well as small (1´) scales. This implies a strong connection between large dust grains and the elusive band carriers; the evolutionary history and heating energy source of these populations must be strongly linked. The average mid-infrared spectrum of the Milky Way is found to be GROUP the average spectrum of spiral galaxy NGC 891 GROUP The common spectrum can therefore be used as a template for the 6–12 $\rm{\mu m}$ emission of late-type spiral galaxies. Finally, we show that interstellar extinction only weakly influences the observed features even at $\lambda = 10\rm{\mu m}$, where the silicate absorption feature is strongest.

The Small Magellanic Cloud in the far infrared - I. ISO's 170 $\mu$m map and revisit of the IRAS 12–100 $\mu$m data

Abstract: The ISOPHOT experiment onboard the ISO satellite generated a complete view of the Small Magellanic Cloud (SMC) at 170 µm with 1.5 arcmin resolution. The map is analysed using an automated photometry program enabling accurate photometric characterization of the far infrared (FIR) emitting regions. An integrated FIR luminosity of 8 .5×10 7 Lis obtained, leading to a star formation rate of SFRFIR = 0.015 M� /yr. With an average dust temperature of , the total dust mass follows to MD = 3.7 × 10 5 M� . In this paper, the sources detected at 170 µm are compared with those obtainable from the IRAS satellite data. For this purpose, the 12 µm, 25 µm, 60 µm, and 100 µm IRAS high resolution (HiRes) maps of the SMC are re-examined using the same method. In contrast to former studies, this provides an all-band ISO/IRAS source catalog which is no longer based on eyeball classification, but relies on an algorithm which is capable of automated, repeatable photometry, even for irregular sources. In the mid infrared IRAS bands numerous bright FIR emitting regions in the SMC are detected and classified: 73 sources are found at 12 µm, 135 at 25 µm (most of them with Fν 30 K) for the first time. A comparison with earlier IRAS results suggests that many source flux densities in those studies have been under- or overestimated because of non-standardized fitting methods. Many sources with flux densities up to 40 Jy listed in former catalogs cannot be identified in our data.

Unidentified Infrared Bands in the Interstellar Medium across the Galaxy

Abstract: We present a set of 6-12 micron ISOPHOT-S spectra of the general interstellar medium of the Milky Way. This part of the spectrum is dominated by a series of strong, wide emission features commonly called the Unidentified Infrared Bands. The sampled area covers the inner Milky Way from l = -60 degr to +60 degr with a ten-degree step in galactic longitude and nominal latitudes 0,+-1 degr. For each grid position the actual observed direction was selected from IRAS 100 micron maps to minimize contamination by point sources and molecular clouds. All spectra were found to display the same spectral features. Band ratios are independent of band strength and Galactic coordinates. A comparison of total observed flux in band features and IRAS 100 micron emission, a tracer for large interstellar dust grains, shows high correlation at large as well as small 1-arcmin scales. This implies a strong connection between large dust grains and the elusive band carriers; the evolutionary history and heating energy source of these populations must be strongly linked. The average mid-infrared spectrum of the Milky Way is found to be similar to the average spectrum of spiral galaxy NGC 891 and the spectra of other spirals. The common spectrum can therefore be used as a template for the 6-12 micron emission of late-type spiral galaxies. Finally, we show that interstellar extinction only weakly influences the observed features even at lambda = 10 microns, where the silicate absorption feature is strongest.

Small-scale structure of the galactic cirrus emission

Abstract: We examined the Fourier power spectrum characteristics of cirrus structures in 13 sky fields with faint to bright cirrus emission observed with ISOPHOT in the 90-200 µm wavelength range in order to study variations of the spectral index α .W e found that α varies from field to field with -5.3 ≤ α ≤-2.1. It depends on the absolute surface brightness and on the hydrogen column density. We also found different spectral indices for the same sky region at different wavelengths. Longer wavelength measurements show steeper power spectra. This can be explained by the presence of dust at various temperatures, in particular of a cold extended component. For the faintest areas of the far-infrared sky we derive a wavelength-independent spectral index of α = -2.3 ± 0.6 for the cirrus power spectrum. The application of the correct spectral index is a precondition for the proper disentanglement of the cirrus foreground component of the Cosmic Far-Infrared Background and its fluctuations.

Far infrared observations of pre-protostellar sources in Lynds 183

Abstract: Using ISOPHOT maps at 100 and 200 μ m and raster scans at 100, 120, 150 and 200 μ m we have detected four unresolved far-infrared sources in the high latitude molecular cloud L 183. Two of the sources are identified with 1.3 mm continuum sources found by Ward-Thompson et al. ([CITE], [CITE]) and are located near the temperature minimum and the coincident column density maximum of dust distribution. For these two sources, the ISO observations have enabled us to derive temperatures (~8.3 K) and masses (~1.4 and 2.4 $M_{\odot}$). They are found to have masses greater than or comparable to their virial masses and are thus expected to undergo gravitational collapse. We classify them as pre-protostellar sources. The two new sources are good candidates for pre-protostellar sources or protostars within L 183.

A very young star forming region detected by the ISOPHOT Serendipity Survey

Abstract: We present a multi-wavelength study of the star forming region ISOSS J 20298+3559, which was identified by a cross-correlation of cold compact sources from the 170 μ m ISOPHOT Serendipity Survey (ISOSS) database coinciding with objects detected by the MSX, 2MASS and IRAS infrared surveys. ISOSS J 20298+3559 is associated with a massive dark cloud complex ( M ~ 760 $M_{\odot}$) and located in the Cygnus X giant molecular cloud. We derive a distance of 1800 pc on the basis of optical extinction data. The low average dust temperature ( T ~ 16 K) and large mass ( M ~ 120 $M_{\odot}$) of the dense inner part of the cloud, which has not been dispersed, indicates a recent begin of star formation. The youth of the region is supported by the early evolutionary stage of several pre- and protostellar objects discovered across the region: I) two candidate Class 0 objects with masses of 8 and 3.5 $M_{\odot}$, II) a gravitationally bound, cold ( T ~ 12 K) and dense ( n (H 2 ) ~ 2 $\times$ 10 5 cm -3 ) cloud core with a mass of 50 $M_{\odot}$ and III) a Herbig B2 star with a mass of 6.5 $M_{\odot}$ and a bolometric luminosity of 2200 $L_{\odot}$, showing evidence for ongoing accretion and a stellar age of less than 40 000 years. The dereddened SED of the Herbig star is well reproduced by an accretion disc + star model. The externally-heated cold cloud core is a good candidate for a massive pre-protostellar object. The star formation efficiency in the central cloud region is about 14%.

NGST MIRI instrument

Abstract: The MIRI is the mid-IR (5-28μm) instrument for NGST and provides for imaging, cororographic, high- and low-resolution spectroscopic capabilities. Unlike to the other instruments on NGST, the MIRI must be cooled - to reduce the thermal background from the optics and because the detectors require an operating temperature of about 7k.. In this paper we summarise the science goals, the proposed overall opto-mechanical concept, the thermal design aspects, the detectors and the expected sensitivity of the instrument.

A gas and dust rich giant elliptical galaxy in the ISOPHOT Serendipity Survey

Abstract: We present a multi-wavelength study of the unusual galaxy ISOSS J 15079+7247. With a bolometric luminosity of LFIR ∼ 2 × 10 12 Lthis object is one of the most luminous galaxies detected by the 170 µm ISOPHOT Serendipity Survey (ISOSS). We have obtained 1.2 mm continuum and CO (1-0) line observations, optical spectra and deep R-band images of the system. The CO emission originates from a giant elliptical galaxy at redshift z = 0.2136, yielding a molecular gas mass of 2.9 × 10 10 M� . The high gas mass favors the picture that the dust emission is associated with the elliptical galaxy. The nature of the ultraluminous IR emission can be explained by an opaque, hidden starburst in the center of the elliptical. The huge dust mass of 5 × 10 8 Mcorresponds to a visual extinction of AV ∼ 1000 mag. This is consistent with the non-detection of any optical signatures of a strong starburst in ISOSS J 15079+7247 and the strength of non-thermal radio continuum emission.

Cryomechanisms for positioning the optical components of the mid-infrared instrument (MIRI) for NGST

Abstract: Mechanisms operating in the cryovacuum are required to rotate filter and dichroic wheels, to tilt gratings and to flip in the beam of an internal calibration source. The design proposed here is based on similar mechanisms flown successfully on the liquid helium cooled European ISO-satellite and being presently under qualification for ESA's cooled HERSCHEL-satellite. Their main characteristics are high reliability during the 10 year lifetime in space, high precision and low heat dissipation in the cryovacuum.

Cryomechanisms for the instruments MIRI and NIRSpec on the James Webb Space Telescope (JWST)

Abstract: The Mid-Infrared Instrument (MIRI) and the Near-Infrared Spectrograph (NIRSpec) of the JWST require various mechanisms for positioning optical elements in cryo-vacuum environment (7K resp. 35K): Wheels for exchanging filters, gratings and prisms, a flip mirror for switching between the sky and internal calibration sources and a linear actuator for refocusing purposes will have to be developed. In order to fulfill the stringent requirements of the mission, comprising to survive a warm ARIANE 5 launch, to guarantee high accuracy positioning in the cryovacuum with minimal power dissipation, to be operational with high reliability during 10 years of lifetime and to be testable under various environmental conditions, we propose a low cost and low schedule risk approach, based on the successful flight experience and qualification heritage from ESA’s infrared missions ISO and HERSCHEL.