Interstellar Extinction Law toward the Galactic Center II: V, J, H, and Ks Bands

TL;DR

This study measures the interstellar extinction ratios toward the Galactic center in optical and near-infrared bands, revealing a steep decline in extinction at longer wavelengths and a notably small Ks band extinction.

Contribution

It provides direct observational extinction ratios in V, J, H, and Ks bands toward the Galactic center, refining the understanding of the extinction law in this region.

Findings

Extinction ratios A(V)/E(V-J)=1.251±0.014 and A(J)/E(V-J)=0.225±0.007.

Derived extinction ratios A(J)/A(V)=0.188±0.005 and A(V):A(J):A(H):A(Ks)=1:0.188:0.108:0.062.

Ks band extinction is approximately 1/16 of A(V), much smaller than previously assumed.

Abstract

We have determined the ratios of total to selective extinction directly from observations in the optical V band and near-infrared J band toward the Galactic center. The OGLE (Optical Gravitational Lensing Experiment) Galactic bulge fields have been observed with the SIRIUS camera on the IRSF telescope, and we obtain A(V)/E(V-J)=1.251+-0.014 and A(J)/E(V-J)=0.225+-0.007. From these ratios, we have derived A(J)/A(V) = 0.188+-0.005; if we combine A(J)/A(V) with the near-infrared extinction ratios obtained by Nishiyama et al. for more reddened fields near the Galactic center, we get A(V) : A(J) : A(H) : A(Ks) = 1 : 0.188 : 0.108 : 0.062, which implies steeply declining extinction toward the longer wavelengths. In particular, it is striking that the Ks band extinction is \approx 1/16 of the visual extinction A(V) much smaller than one tenth of A(V) so far employed.