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تسجيل مستخدم جديدVLA and GBT Observations of Orion B (NGC 2024, W12) : Photo-dissociation Region Properties and Magnetic field
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D. Anish Roshi
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We present images of C110$alpha$ and H110$alpha$ radio recombination line (RRL) emission at 4.8 GHz and images of H166$alpha$, C166$alpha$ and X166$alpha$ RRL emission at 1.4 GHz, observed toward the starforming region NGC 2024. The 1.4 GHz image with angular resolution $sim$ 70arcsec is obtained using VLA data. The 4.8 GHz image with angular resolution $sim$ 17arcsec is obtained by combining VLA and GBT data. The similarity of the LSR velocity (10.3 kms) of the C110$alpha$ line to that of lines observed from molecular material located at the far side of the HII region suggests that the photo dissociation region (PDR) responsible for C110$alpha$ line emission is at the far side. The LSR velocity of C166$alpha$ is 8.8 kms. This velocity is comparable with the velocity of molecular absorption lines observed from the foreground gas, suggesting that the PDR is at the near side of the HII region. Non-LTE models for carbon line forming regions are presented. Typical properties of the foreground PDR are $T_{PDR} sim 100$ K, $n_e^{PDR} sim 5$ cmthree, $n_H sim 1.7 times 10^4$ cmthree, path length $l sim 0.06$ pc and those of the far side PDR are $T_{PDR} sim$ 200 K, $n_e^{PDR} sim$ 50 cmthree, $n_H sim 1.7 times 10^5$ cmthree, $l sim$ 0.03 pc. Our modeling indicates that the far side PDR is located within the HII region. We estimate magnetic field strength in the foreground PDR to be 60 $mu$G and that in the far side PDR to be 220 $mu$G. Our field estimates compare well with the values obtained from OH Zeeman observations toward NGC 2024.
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