Modeling the infrared extinction toward the galactic center

Jian Gao,Aigen Li,B W Jiang

doi:10.5047/eps.2013.05.016

Jian Gao, Aigen Li + Show 1 more

Open Access

https://doi.org/10.5047/eps.2013.05.016

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Abstract

We model the ~ 1–19 μ m infrared (IR) extinction curve toward the Galactic Center (GC) in terms of the standard silicate-graphite interstellar dust model. The grains are taken to have a power law size distribution with an exponential decay above some size. The best-fit model for the GC IR extinction constrains the visual extinction to be AV ~ 38–42 mag. The limitation of the model, i.e., its difficulty in simultaneously reproducing both the steep ~ 1–3 μ m near-IR extinction and the flat ~ 3–8 μ m mid-IR extinction is discussed. We argue that this difficulty could be alleviated by attributing the extinction toward the GC to a combination of dust in different environments: dust in diffuse regions (characterized by small RV and steep near-IR extinction), and dust in dense regions (characterized by large RV and flat UV extinction).

Highlights

The wavelength dependence of the interstellar extinction—known as the “interstellar extinction law”—is one of the primary sources of information about the interstellar grain population (Draine, 2003)
We model the ∼ 1–19 μm infrared (IR) extinction curve toward the Galactic Center (GC) in terms of the standard silicate-graphite interstellar dust model
The limitation of the model, i.e., its difficulty in simultaneously reproducing both the steep ∼ 1–3 μm near-IR extinction and the flat ∼ 3–8 μm mid-IR extinction is discussed. We argue that this difficulty could be alleviated by attributing the extinction toward the GC to a combination of dust in different environments: dust in diffuse regions, and dust in dense regions

Summary

Introduction

The wavelength dependence of the interstellar extinction—known as the “interstellar extinction law (or curve)”—is one of the primary sources of information about the interstellar grain population (Draine, 2003). It is worth noting that the flat MIR extinction curves determined for various sightlines all appear to agree with the extinction predicted by the standard silicate-graphite interstellar grain model for RV = 5.5 (Weingartner and Draine, 2001) (hereafter WD01), which indicates a dust size distribution favoring larger sizes compared to that for RV = 3.1. We try to use the standard interstellar grain model which consists of graphite and silicate grains (Draine and Lee, 1984) to fit the observed IR extinction curve toward the GC of Fritz et al (2011) and constrain the total optical extinction (AV) toward the GC. For Si, they adopt the solar abundance of Si/H = 3.63 × 10−5, but assuming a complete depletion in dust Their CASE A models tried to seek the best fit by varying the total volume per H in

Findings

Model Extinction

Discussion