Line-of-Sight Reddening Predictions: Zero Points, Accuracies, the Interstellar Medium, and the Stellar Populations of Elliptical Galaxies

Revised (B-V)_0-Mg_2 data for 402 elliptical galaxies are given to test reddening predictions which can also tell us both what the intrinsic errors are in this relationship among gE galaxy stellar populations, as well as details of nearby structure in the interstellar medium (ISM) of our Galaxy and of the intrinsic errors in reddening predictions. Using least-squares fits, the explicit 1-sigma errors in the Burstein-Heiles (BH) and the Schlegel et al. (IR) predicted reddenings are calculated, as well as the 1-sigma observational error in the (B-V)_0-Mg_2 for gE galaxies. It is found that, in directions with E(B-V)<0.100 mag (where most of these galaxies lie), 1-sigma errors in the IR reddening predictions are 0.006 to 0.009 in E(B-V) mag, those for BH reddening prediction are 0.011 mag, and the 1-sigma agreement between the two reddening predictions is 0.007 mag. IR predictions have an accuracy of 0.010-0.011 mag in directions with E(B-V)>= 0.100 mag, significantly better than those of the BH predictions (0.024-0.025). Gas-to-dust variations that vary by a factor of 3, both high and low, exist along many lines-of-sight in our Galaxy. The approx 0.02 higher reddening zero point in E(B-V) previously determined by Schlegel et al. is confirmed, primarily at the Galactic poles. Despite this, both methods also predict many directions with E(B-V)<0.015 mag. Independent evidence of reddening at the North Galactic pole is reviewed, with the conclusion that there still exists directions at the NGP that have E(B-V)<<0.01. Two lines of evidence suggest that IR reddenings are overpredicted in directions with high gas-to-dust ratios. As high gas-to-dust directions in the ISM also include the Galactic poles, this overprediction is the likely cause of the E(B-V) = 0.02 mag larger IR reddening zero point.Comment: 5 figure

Experimental Phase Function and Degree of Linear Polarization Curves of Millimeter- sized Cosmic Dust Analogs

International audienceWe present laboratory measurements of the phase functions and degree of linear polarization (DLP) curves of a selection of millimeter-sized cosmic dust analog particles. The set includes particles with similar sizes but diverse internal structure (compact and porous) and absorbing properties. The measured phase functions are found to be in all cases very different from those of micron-sized particles. They show a monotonic decrease with increasing phase angle from the back- to the side-scattering region, reaching a minimum at large phase angles before a steep increase of the forward peak. This is in stark contrast to the phase functions of micron-sized particles, which are rather flat at low and intermediate phase angles. The maximum of the DLP for millimeter-sized compact particles is shifted toward larger phase angles (∼130°) compared to that of micron-sized particles (∼90°). Porosity plays an important role in the measured DLP curves: the maximum significantly decreases for increasing porosity as a result of multiple scattering within the particle. Large porous particles with highly absorbing inclusions can reproduce both the OSIRIS/Rosetta phase functions and ground-based DLP observations of comet 67P/Churyumov-Gerasimenko

Experimental Phase Function and Degree of Linear Polarization Curves of Millimeter-sized Cosmic Dust Analogs

We present laboratory measurements of the phase functions and degree of linear polarization (DLP) curves of a selection of millimeter-sized cosmic dust analog particles. The set includes particles with similar sizes but diverse internal structure (compact and porous) and absorbing properties. The measured phase functions are found to be in all cases very different from those of micron-sized particles. They show a monotonic decrease with increasing phase angle from the back- to the side-scattering region, reaching a minimum at large phase angles before a steep increase of the forward peak. This is in stark contrast to the phase functions of micron-sized particles, which are rather flat at low and intermediate phase angles. The maximum of the DLP for millimeter-sized compact particles is shifted toward larger phase angles (~130°) compared to that of micron-sized particles (~90°). Porosity plays an important role in the measured DLP curves: the maximum significantly decreases for increasing porosity as a result of multiple scattering within the particle. Large porous particles with highly absorbing inclusions can reproduce both the OSIRIS/Rosetta phase functions and ground-based DLP observations of comet 67P/Churyumov–Gerasimenko

Experimental phase function and degree of linear polarization curves of mm-sized cosmic dust analogs

International audienc