Infrared excess and molecular clouds : A comparison of new surveys of far - Infrared and H I 21 - cm emission at high latitudes

We have created a map of the large-scale infrared surface brightness in excess of that associated with the atomic interstellar medium, using region-by-region correlations between the far-infrared and 21-cm line surface brightness. Our study updates and extends a previous attempt with the Infrared Astronomical Satellite and Berkeley/Parkes H I surveys. The far-infrared observations used here are from the Cosmic Background Explorer Diffuse Infrared Background Experiment, which extends far-infrared wavelength coverage to 240 μm, so that we are reliably sampling the emission of large, thermal-equilibrium grains that dominate the dust mass. The H I data are from the combined Leiden-Dwingeloo and Parkes 21-cm line surveys. Using the maps of excess infrared emission at 100, 140, and 240 μm, we created an atlas and identified the coherent structures. These infrared excess clouds can be caused both by dust that is warmer than average, or by dust associated with gas other than the atomic interstellar medium. We find very few warm clouds, such as the H II region around the high-latitude B-type star α Vir. The majority of the infrared excess clouds are colder than the average atomic interstellar medium. These clouds are peaks of column density, and their excess infrared emission is due to dust associated with molecular gas. We identify essentially all known high-latitude molecular clouds in the infrared excess maps, and further identify a sample of new clouds with similar infrared properties. The infrared excess was correlated with CO line brightness, allowing us to measure