Near-Infrared Extinction in The Coalsack Globule 2

Abstract

We have conducted J, H, and Ks imaging observations for the Coalsack Globule 2 with the SIRIUS infrared camera on the IRSF 1.4 m telescope at SAAO, and determined the color excess ratio, E(J-H)/E(H-Ks). The ratio is determined in the same photometric system as our previous study for the rho Oph and Cha clouds without any color transformation; this enables us to directly compare the near-infrared extinction laws among these regions. The current ratio E(J-H)/E(H-Ks) = 1.91 +- 0.01 for the extinction range 0.5 < E(J-H) <1.8 is significantly larger than the ratios for the rho Oph and Cha clouds (E(J-H)/E(H-Ks) = 1.60-1.69). This ratio corresponds to a large negative index alpha = 2.34 +- 0.01 when the wavelength dependence of extinction is approximated by a power law which might indicate little growth of dust grains, or larger abundance of dielectric non-absorbing components such as silicates, or both in this cloud. We also confirm that the color excess ratio for the Coalsack Globule 2 has a trend of increasing with decreasing optical depth, which is the same trend as the rho Oph and Cha clouds have.

arXiv comment13 pages, 5 figures, and 2 tables, ApJ

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• 86 GHz SiO maser survey of late-type stars in the Inner Galaxy III. Interstellar extinction and colours of the SiO targets
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• Line derived infrared extinction towards the Galactic Center
• The Mid-Infrared Extinction Law and its Variation in the Coalsack Nebula
• Evidence for Grain Growth in Molecular Clouds: A Bayesian Examination of the Extinction Law in Perseus
• Impact of distance determinations on Galactic structure. I. Young and intermediate-age tracers
• Near-Infrared Circular Polarimetry and Correlation Diagrams in the Orion BN/KL Region: Contribution of Dichroic Extinction
• UV Extinction as a More Fundamental Measure of Dust than E(B-V) or A(V)