Poster

Modeling the Infrared Extinction Law and Reestimating the Extinction at the Visual Band towards the Galactic Center

¹Jian Gao, ²Aigen Li, ¹Biwei Jiang (¹Beijing Normal University, ²Universtiy of Missouri)

Towards the Galactic center (GC), the recent observed extinction curve by Fritz et al. (2011) shows a steeper near-infrared (NIR) extinction than the one obtained by previous studies, and shows a same flat mid-infrared (MIR) extinction consistent with the one towards other sightlines. Using a mixed dust model consisting of graphite grains and amorphous silicate grains with a dust grain size distribution dn/da ~ a^axe^(-a/ac) (50Å < a < 1 mm), we fitted the extinction curve towards the GC from 1 to 19 mm. Our dust model can well model the standard average extinction curve of Rv = 3.1 for the diffuse interstellar medium. Although it can reproduce the steep NIR extinction and the strong silicate features, the fitting results show that the dust model isn't good enough to reproduce the flat extinction in the MIR wavelength range. Some groups of dust grains with different size distribution or something else may be necessary to explain the flat MIR extinction towards many different sightlines. Our best modeled extinction curve shows that the extinction at the visual band Av is about 38 - 42 mag, larger than the previous estimated Av ~ 31 towards the GC. In the meanwhile, from the ultraviolet (UV) to NIR wavelength range, the modeled extinction curve shows that the extinction towards the GC is more similar to the theoretical extinction curve of Rv = 2.1, rather than the one with Rv = 3.1. The extinction curve toward the GC obtained by Fritz et al. (2011) may be a combination with the steep extinction from UV to NIR bands of Rv = 2.1, the flat MIR extinction of Rv = 5.5, and the strong silicate absorption features of Rv = 3.1.

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