Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published May 20, 2012 | Published
Journal Article Open

Evidence for Environmental Changes in the Submillimeter Dust Opacity


The submillimeter opacity of dust in the diffuse interstellar medium (ISM) in the Galactic plane has been quantified using a pixel-by-pixel correlation of images of continuum emission with a proxy for column density. We used multi-wavelength continuum data: three Balloon-borne Large Aperture Submillimeter Telescope bands at 250, 350, and 500 μm and one IRAS band at 100 μm. The proxy is the near-infrared color excess, E(J – K_s), obtained from the Two Micron All Sky Survey. Based on observations of stars, we show how well this color excess is correlated with the total hydrogen column density for regions of moderate extinction. The ratio of emission to column density, the emissivity, is then known from the correlations, as a function of frequency. The spectral distribution of this emissivity can be fit by a modified blackbody, whence the characteristic dust temperature T and the desired opacity σ_e(1200) at 1200 GHz or 250 μm can be obtained. We have analyzed 14 regions near the Galactic plane toward the Vela molecular cloud, mostly selected to avoid regions of high column density (N_H > 10^(22) cm^(–2)) and small enough to ensure a uniform dust temperature. We find σ_e(1200) is typically (2-4) × 10^(–25) cm^2 H^(–1) and thus about 2-4 times larger than the average value in the local high Galactic latitude diffuse atomic ISM. This is strong evidence for grain evolution. There is a range in total power per H nucleon absorbed (and re-radiated) by the dust, reflecting changes in the strength of the interstellar radiation field and/or the dust absorption opacity. These changes in emission opacity and power affect the equilibrium T, which is typically 15 K, colder than at high latitudes. Our analysis extends, to higher opacity and lower temperature, the trend of increasing σ_e(1200) with decreasing T that was found at high latitudes. The recognition of changes in the emission opacity raises a cautionary flag because all column densities deduced from dust emission maps, and the masses of compact structures within them, depend inversely on the value adopted.

Additional Information

© 2012 American Astronomical Society. Received 2011 December 22; accepted 2012 March 14; published 2012 May 1. The BLAST collaboration acknowledges the support of NASA through grant numbers NAG5-12785, NAG5-13301, and NNGO-6GI11G, the Canadian Space Agency (CSA), the UK Particle Physics & Astronomy Research Council (PPARC), and Canada's Natural Sciences and Engineering Research Council (NSERC). We thank the Columbia Scientific Balloon Facility (CSBF) staff for their outstanding work. Finally, we appreciate the careful reading of the manuscript by the referee, B. T. Draine, which has led to some clarification and elaboration of the analysis.

Attached Files

Published - Martin2012p18398Astrophys_J.pdf


Files (944.3 kB)
Name Size Download all
944.3 kB Preview Download

Additional details

August 22, 2023
October 17, 2023