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Astron. Astrophys. 332, 739-747 (1998)

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Small-scale structures in the far-infrared background *

Uwe Herbstmeier 1, Péter Ábrahám 1, 2, Dietrich Lemke 1, R.J. Laureijs 3, Ulrich Klaas 1, 3, Kalevi Mattila 4, Christoph Leinert 1, Christian Surace 1 and Michael Kunkel 1

1 Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
2 Konkoly Observatory of the Hungarian Academy of Sciences, P.O. Box 67, 1525 Budapest, Hungary
3 ISO Science Operation Centre, Astrophysics Division, Space Science Department of ESA, Villafranca, P.O. Box 50727, E-28080 Madrid, Spain
4 University of Helsinki, Observatory, P.O. Box 14, Tähtitorninmäki, FIN-00014 Helsinki, Finland

Received 22 September 1997 / Accepted 20 January 1998

Abstract

Four fields with areas ranging from 80 to 2000 arcmin2 have been mapped with the photometer on board of the Infrared Space Observatory (ISO) at 90 and around 180 µm 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 90 µm 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 180 µm 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 [FORMULA] as for the 90 µm component is found. For cirrus clouds the spatial frequency spectrum in the far-infrared has a similar shape as that derived from 21 cm line observations of the interstellar neutral hydrogen. In faint regions the fluctuations are caused presumably by randomly distributed extragalactic sources. Future 3 m class space telescopes surveying the sky around 200 µm will not be hampered by cirrus over most of the sphere.

Key words: methods: observational – ISM: structure – Infrared: ISM: continuum – diffuse radiation

* 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

Send offprint requests to: Uwe Herbstmeier (uherbst@mpia-hd.mpg.de)

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© European Southern Observatory (ESO) 1998

Online publication: March 23, 1998
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