Extinction Ratios in the Inner Galaxy as Revealed by the VVV Surve

摘要

Interstellar extinction toward the Galactic Center (GC) is large and significantly differential. Its reddening and dimming effects in red clump (RC) stars in the Galactic Bulge can be exploited to better constrain the extinction law toward the innermost Galaxy. By virtue of a deep and complete catalog of more than 30 million objects at ∣l∣≤ 2°.7 and ∣b∣≤ 1°.55 obtained from VVV survey observations, we apply the RC method to infer the selective-to-total extinction ratios in the Z, Y, J, H, and K_s broadband near-infrared filters. The measured values are smaller than previously reported, and are not constant, with mean values of, e.g., A_KS/E(J - K_s) = 0.428 ± 0.005 ± 0.04 and A_KS/E(H - K_s) = 1.104 ± 0.022 ± 0.2. We also obtain a ratio A_Z:A_Y:A_J:A_H:A_KS of 7.74:5.38:3.30:1.88:1.0, implying extinction toward the GC to follow a distribution as a function of wavelength steeper than previously reported, consistent with a power law Aλ ∝ λ~(-2.47) in the near-infrared.