Line derived infrared extinction towards the Galactic Center

TL;DR

This study derives the infrared extinction curve towards the Galactic Center using hydrogen emission lines and continuum observations, revealing a grayer extinction at longer wavelengths and suggesting complex dust composition.

Contribution

It provides the first detailed extinction curve from 1 to 19 microns towards the Galactic Center, incorporating composite dust models including ices.

Findings

Extinction at 2.166 microns is 2.62 +/- 0.11.

Extinction slope shortward of 2.8 microns is -2.11 +/- 0.06.

Dust models require composite particles with ices to fit the observations.

Abstract

We derive the extinction curve towards the Galactic Center from 1 to 19 micron. We use hydrogen emission lines of the minispiral observed by ISO-SWS and SINFONI. The extinction free flux reference is the 2 cm continuum emission observed by the VLA. Towards the inner 14" * 20" we find an extinction of A(2.166 micron)=2.62 +/- 0.11, with a power-law slope of alpha=-2.11 +/- 0.06 shortward of 2.8 micron, consistent with the average near infrared slope from the recent literature. At longer wavelengths, however, we find that the extinction is grayer than shortward of 2.8 micron. We find it is not possible to fit the observed extinction curve with a dust model consisting of pure carbonaceous and silicate grains only, and the addition of composite particles, including ices, is needed to explain the observations. Combining a distance dependent extinction with our distance independent extinction we derive the distance to the GC to be R_0=7.94 +/- 0.65 kpc. Towards Sgr A* (r<0.5") we obtain A_H=4.21 +/- 0.10, A_Ks=2.42 +/- 0.10 and A_L'=1.09 +/- 0.13.