Person:

Finkbeiner, Douglas

We present predicted full-sky maps of submillimeter and microwave emission from the diffuse interstellar dust in the Galaxy. These maps are extrapolated from the 100 μm emission and 100/240 μm flux ratio maps that Schlegel, Finkbeiner, & Davis generated from IRAS and COBE/DIRBE data. Results are presented for a number of physically plausible emissivity models. The correlation of COBE/FIRAS data with the simple Schlegel, Finkbeiner, & Davis (ν2 emissivity power law) extrapolation is much tighter than with other common dust templates such as H I column density or 100 μm emission. Despite the apparent success of the Schlegel, Finkbeiner, & Davis extrapolation, the assumed ν2 emissivity is inconsistent with the FIRAS data below 800 GHz. Indeed, no power-law emissivity function fits the FIRAS data from 200 to 2100 GHz. In this paper we provide a formalism for a multicomponent model for the dust emission. A two-component model with a mixture of "silicate" and "carbon-dominated" grains (motivated by Pollack et al.) provides a fit to an accuracy of ~15% to all the FIRAS data over the entire high-latitude sky. Small systematic differences are found between the atomic and molecular phases of the ISM. COBE/DMR has observed microwave emission that is correlated with thermal dust emission. However, this emission is higher than our model predicts by factors of 1.2, 2.4, and 20 at 90, 53, and 31 GHz, respectively. This provides evidence that another emission mechanism dominates dust emission at frequencies below ~60 GHz. Our predictions for the thermal (vibrational) emission from Galactic dust at ν < 3000 GHz are available for general use. These full-sky predictions can be made at the DIRBE resolution of 40' or at the higher resolution of 6farcm1 from the Schlegel, Finkbeiner, & Davis DIRBE-corrected IRAS maps.

We present a full-sky 100 μm 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 μm data, we have constructed a map of the dust temperature so that the 100 μm 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 μm 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 μm flux. This procedure removes virtually all traces of the zodiacal foreground. For the 100 μm 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 μm and of 17 ± 4 nW m-2 sr-1 at 240 μm (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 μm 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