Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds
- ISSN: 0004637X
- DOI: 10.1086/305772
- arXiv: astro-ph/9710327v2
Abstract
We present a full-sky 100 mu m map that is a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed. Before using the ISSA maps, we remove the remaining artifacts from the IRAS scan pattern. Using the DIRBE 100 and 240 mu m data, we have constructed a map of the dust temperature so that the 100 mu m map may be converted to a map proportional to dust column density. The dust temperature varies from 17 to 21 K, which is modest but does modify the estimate of the dust column by a factor of 5. The result of these manipulations is a map with DIRBE quality calibration and IRAS resolution. A wealth of filamentary detail is apparent on many different scales at all Galactic latitudes. In high-latitude regions, the dust map correlates well with maps of H I emission, but deviations are coherent in the sky and are especially conspicuous in regions of saturation of H I emission toward denser clouds and of formation of H2 in molecular clouds. In contrast, high-velocity H I clouds are deficient in dust emission, as expected. To generate the full-sky dust maps, we must first remove zodiacal light contamination, as well as a possible cosmic infrared background (CIB). This is done via a regression analysis of the 100 mu m DIRBE map against the Leiden-Dwingeloo map of H I emission, with corrections for the zodiacal light via a suitable expansion of the DIRBE 25 mu m flux. This procedure removes virtually all traces of the zodiacal foreground. For the 100 mu m map no significant CIB is detected. At longer wavelengths, where the zodiacal contamination is weaker, we detect the CIB at surprisingly high flux levels of 32 13 nW m-2 sr-1 at 140 mu m and of 17 4 nW m-2 sr-1 at 240 mu m (95% confidence). This integrated flux ~2 times that extrapolated from optical galaxies in the Hubble Deep Field. The primary use of these maps is likely to be as a new estimator of Galactic extinction. To calibrate our maps, we assume a standard reddening law and use the colors of elliptical galaxies to measure the reddening per unit flux density of 100 mu m emission. We find consistent calibration using the B-R color distribution of a sample of the 106 brightest cluster ellipticals, as well as a sample of 384 ellipticals with B-V and Mg line strength measurements. For the latter sample, we use the correlation of intrinsic B-V versus Mg2 index to tighten the power of the test greatly. We demonstrate that the new maps are twice as accurate as the older Burstein-Heiles reddening estimates in regions of low and moderate reddening. The maps are expected to be significantly more accurate in regions of high reddening. These dust maps will also be useful for estimating millimeter emission that contaminates cosmic microwave background radiation experiments and for estimating soft X-ray absorption. We describe how to access our maps readily for general use.
Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds
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Maps of Dust IR Emission for Use in Estimation of Reddening
and CMBR Foregrounds
David J. Schlegel
University of Durham, Department of Physics, South Road, Durham DH1 3LE, United
Kingdom
and
Douglas P. Finkbeiner & Marc Davis
University of California at Berkeley, Departments of Physics and Astronomy, 601 Campbell
Hall, Berkeley, CA 94720
ABSTRACT
We present a full sky 100µm map that is a reprocessed composite of
the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and
confirmed point sources removed. Before using the ISSA maps, we remove the
remaining artifacts from the IRAS scan pattern. Using the DIRBE 100µm and
240µm data, we have constructed a map of the dust temperature, so that the
100µm map may be converted to a map proportional to dust column density.
The dust temperature varies from 17 K to 21 K, which is modest but does
modify the estimate of the dust column by a factor of 5. The result of these
manipulations is a map with DIRBE-quality calibration and IRAS resolution. A
wealth of filamentary detail is apparent on many different scales at all Galactic
latitudes. In high latitude regions, the dust map correlates well with maps of H I
emission, but deviations are coherent in the sky and are especially conspicuous
in regions of saturation of H I emission toward denser clouds and the formation
of H2 in molecular clouds. In contrast, high-velocity H I clouds are deficient in
dust emission, as expected.
To generate the full sky dust maps, we must first remove zodiacal light
contamination as well as a possible cosmic infrared background (CIB). This
is done via a regression analysis of the 100µm DIRBE map against the
Leiden-Dwingeloo map of H I emission, with corrections for the zodiacal light
via a suitable expansion of the DIRBE 25µm flux. This procedure removes
virtually all traces of the zodiacal foreground. For the 100µm map no significant
CIB is detected. At longer wavelengths, where the zodiacal contamination is
weaker, we detect the CIB at surprisingly high flux levels of 32± 13 nW/m2/sr
at 140µm, and 17 ± 4 nW/m2/sr at 240µm (95% confidence). This integrated
flux is ∼ 2 times that extrapolated from optical galaxies in the Hubble Deep
Field.
The primary use of these maps is likely to be as a new estimator of Galactic
extinction. To calibrate our maps, we assume a standard reddening law, and use
the colors of elliptical galaxies to measure the reddening per unit flux density
of 100µm emission. We find consistent calibration using the (B−R) color
distribution of a sample of 106 brightest cluster ellipticals, as well as a sample of
384 ellipticals with (B−V ) and Mg line-strength measurements. For the latter
sample, we use the correlation of intrinsic (B−V ) versus Mg2 index to greatly
tighten the power of the test. We demonstrate that the new maps are twice as
accurate as the older Burstein-Heiles reddening estimates in regions of low and
moderate reddening. The maps are expected to be significantly more accurate
in regions of high reddening. These dust maps will also be useful for estimating
millimeter emission that contaminates CMBR experiments and for estimating
soft X-ray absorption.
We describe how to readily access our maps for general use.
Subject headings: Cosmology: observations — dust — extinction — infrared:
ISM: continuum
1. Introduction
In the past 15 years, two NASA missions have revolutionized our knowledge of the
diffuse interstellar medium. The path-breaking Infrared Astronomy Satellite (IRAS) mission
of 1983 led to the first full-sky maps of the diffuse background radiation in four broadband
infrared channels, centered at 12, 25, 60, and 100µm, with a ∼ 5 arcminute beam. The
DIRBE experiment (Diffuse InfraRed Background Experiment) onboard the COBE satellite
imaged the full sky in 10 broad photometric bands from 1µm to 240µm with a beam of
0.7◦. This experiment, for all but the shortest wavelength channels, was active for 42
weeks in 1989-1990 before its 4He cryogen was exhausted. Although IRAS was optimized
to detect point sources and sources of small angular extent (Beichman et al. 1988), it has
been possible to create large area sky maps from the IRAS data stream (ISSA images:
Wheelock et al. 1994). Striping artifacts from time variation in the zodiacal foreground
emission has largely been filtered out of the individual ISSA maps, but artifacts remain and
the zero-point has large-scale drifts across the images. The DIRBE experiment had a much
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