Extinction Law at a Distance up to 25 kpc toward the Galactic Poles

TL;DR

This study analyzes how the infrared interstellar extinction law varies with distance up to 25 kpc toward the Galactic poles, revealing different extinction characteristics near the Galactic plane and halo.

Contribution

It provides the first detailed analysis of the extinction law variation with distance up to 25 kpc toward the Galactic poles using multi-catalog photometry.

Findings

Conventional extinction law applies within 100 pc of the Galactic plane.

Different extinction coefficients are observed in the Galactic halo.

Far from the plane, larger dust grains dominate the extinction properties.

Abstract

Photometry from the Tycho-2, 2MASS, and WISE catalogues for clump and branch giants at a distance up to 25 kpc toward the Galactic poles has allowed the variations of various characteristics of the infrared interstellar extinction law with distance to be analyzed. The results obtained by the extinction law extrapolation method are consistent for different classes of stars and different characteristics as well as with previous studies. The conventional extinction law with a low infrared extinction is characteristic of only a thin layer no farther than 100 pc from the Galactic plane and of two thin layers near $Z=-600$ and $+500$ pc. Far from the Galactic plane, in the Galactic halo, the infrared extinction law is different: the extinction in the $Ks$, $W1$, $W2$, $W3$, and $W4$ bands is, respectively, $0.17$, $0.16$, $0.16$, $0.07$, and $0.03$ of the extinction in the $V$ band. The accuracy of these coefficients is $0.03$. If the extinction law reflects primarily the grain size distribution, then the fraction of large dust grains far from the Galactic plane is greater than that in the circumsolar interstellar medium.