Small Variation of the NIR and MIR Interstellar Extinction Laws

Using the data from APOGEE, WISE, and GLIMPSE, we explored the variation of the near-infrared (NIR) and mid-infrared (MIR) interstellar extinction laws of the Milky Way. We derived the IR extinction laws towards a number of different sightlines, including 24 bins along Galactic latitude (b) and 592 plates observed by APOGEE. Our results indicate that E(J-H)/E(J-K) show only subtle variation along b, Galactic longitude (l), or the depth of E(J-K). This suggests that the NIR extinction law can be considered as universal. Similarly, E(K-W1, W2, W3, [3.6], [4.5], [5.8], [8.0])/E(J-K) also show only small variation along b, l, or the extinction depth. The MIR extinction curve is flat, indicating that the MIR extinction law is likely universal.