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: http://www.stsci.edu/~kgordon/magclouds_results/magclouds_results.html
Дата изменения: Thu Mar 26 20:52:20 2015 Дата индексирования: Sun Apr 10 16:36:55 2016 Кодировка: Поисковые слова: universe |
The dust properties in the Large and Small Magellanic clouds (LMC/SMC) are studied using the HERITAGE Herschel Key Project photometric data in five bands from 100 to 500 µm. Three simple models of dust emission were fit to the observations: a single temperature blackbody modified by a power-law emissivity (SMBB), a single temperature blackbody modified by a broken power-law emissivity (BEMBB), and two blackbodies with different temperatures, both modified by the same power-law emissivity (TTMBB). Using these models, we investigate the origin of the submillimeter excess, defined as the submillimeter emission above that expected from SMBB models fit to observations >200 µm. We find that the BEMBB model produces the lowest fit residuals with pixel-averaged 500 µm submillimeter excesses of 27% and 43% for the LMC and SMC, respectively. Adopting gas masses from previous works, the gas-to-dust ratios calculated from our fitting results show that the TTMBB fits require significantly more dust than are available even if all the metals present in the interstellar medium (ISM) were condensed into dust. This indicates that the submillimeter excess is more likely to be due to emissivity variations than a second population of colder dust. We derive integrated dust masses of (7.3 ± 1.7) × 105 and (8.3 ± 2.1) × 104 M☉ for the LMC and SMC, respectively. We find significant correlations between the submillimeter excess and other dust properties; further work is needed to determine the relative contributions of fitting noise and ISM physics to the correlations.
The full paper is available at ADS in multiple formats. Please see this paper for all the details on how the data and results below were obtained.
Please reference Gordon et. al. 2014, ApJ, 797, 85 if you use these results in a paper, talk, poster, etc. Thanks.
Spatially resolved fits were done using three different dust emission models. The 1st is a single temperature modified by a power law emissivity law (SMBB). The 2nd is the broken emissivity model with dust grains with a single temperature and a broken emissivity law (BEMBB). The 3rd is the two temperature model with 2 dust grains with different temperatures and a single unbroken emissivity law (TTMBB). Each dust emission model provides results in two flavors, depending on the prior/assumption on range of beta values allowed. The set of results are then priors are:
The "best fit" parameters are presented in 3 flavors.
The files are FITS files with extensions. Each extension has a different fit parameter and is identified by the 'extname' keyword in the extension header. The links are to .tar.gz files containing the spearate files.
SMC | LMC |
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These images are convolved to the SPIRE 500 micron resolution (using the Aniano et. al. 2011 kernels, MW foreground subtracted using a scaled version of the MW foreground HI map, and background subtracted (using a 2D polynomical surface to regions outside the galaxy). Note I've also include the HI data with the same background subtraction for consistency. The data come in two forms, "native SPIRE 500" and rebinned to 56" pixels to provide pixels that are nominally independent.
The links are to .tar.gz files containing the spearate files.
The images shown below are ordered:
PACS 100 micron, PACS 160 micron, SPIRE 250 micron
SPIRE 350 micron, SPIRE 500 micron, HI 21 cm
Copyright © 2015 Karl D. Gordon All Rights Reserved