The JWST-NIRCam View of Sagittarius C. II. Evidence for Magnetically Dominated HII Regions in the CMZ
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2024
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| author | Bally, John Crowe, Samuel Fedriani, Rubén Ginsburg, Adam Schödel, Rainer Andersen, Morten Tan, Jonathan C. Li, Zhi-Yun Nogueras-Lara, Francisco Cheng, Yu Law, Chi-Yan Wang, Q. Daniel Zhang, Yichen Zhang, Suinan |
| author_facet | Bally, John Crowe, Samuel Fedriani, Rubén Ginsburg, Adam Schödel, Rainer Andersen, Morten Tan, Jonathan C. Li, Zhi-Yun Nogueras-Lara, Francisco Cheng, Yu Law, Chi-Yan Wang, Q. Daniel Zhang, Yichen Zhang, Suinan |
| contents | We present JWST-NIRCam narrow-band, 4.05 $μ$m Brackett-$α$ images of the Sgr C HII region, located in the Central Molecular Zone (CMZ) of the Galaxy. Unlike any HII region in the Solar vicinity, the Sgr C plasma is dominated by filamentary structure in both Brackett-$α$ and the radio continuum. Some bright filaments, which form a fractured arc with a radius of about 1.85 pc centered on the Sgr C star-forming molecular clump, likely trace ionization fronts. The brightest filaments form a `$π$-shaped' structure in the center of the HII region. Fainter filaments radiate away from the surface of the Sgr C molecular cloud. The filaments are emitting optically thin free-free emission, as revealed by spectral index measurements from 1.28 GHz (MeerKAT) to 97 GHz (ALMA). But, the negative in-band 1 to 2 GHz spectral index in the MeerKAT data alone reveals the presence of a non-thermal component across the entire Sgr C HII region. We argue that the plasma flow in Sgr C is controlled by magnetic fields, which confine the plasma to rope-like filaments or sheets. This results in the measured non-thermal component of low-frequency radio emission plasma, as well as a plasma $β$ (thermal pressure divided by magnetic pressure) below 1, even in the densest regions. We speculate that all mature HII regions in the CMZ, and galactic nuclei in general, evolve in a magnetically dominated, low plasma $β$ regime. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2412_10983 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | The JWST-NIRCam View of Sagittarius C. II. Evidence for Magnetically Dominated HII Regions in the CMZ Bally, John Crowe, Samuel Fedriani, Rubén Ginsburg, Adam Schödel, Rainer Andersen, Morten Tan, Jonathan C. Li, Zhi-Yun Nogueras-Lara, Francisco Cheng, Yu Law, Chi-Yan Wang, Q. Daniel Zhang, Yichen Zhang, Suinan Astrophysics of Galaxies We present JWST-NIRCam narrow-band, 4.05 $μ$m Brackett-$α$ images of the Sgr C HII region, located in the Central Molecular Zone (CMZ) of the Galaxy. Unlike any HII region in the Solar vicinity, the Sgr C plasma is dominated by filamentary structure in both Brackett-$α$ and the radio continuum. Some bright filaments, which form a fractured arc with a radius of about 1.85 pc centered on the Sgr C star-forming molecular clump, likely trace ionization fronts. The brightest filaments form a `$π$-shaped' structure in the center of the HII region. Fainter filaments radiate away from the surface of the Sgr C molecular cloud. The filaments are emitting optically thin free-free emission, as revealed by spectral index measurements from 1.28 GHz (MeerKAT) to 97 GHz (ALMA). But, the negative in-band 1 to 2 GHz spectral index in the MeerKAT data alone reveals the presence of a non-thermal component across the entire Sgr C HII region. We argue that the plasma flow in Sgr C is controlled by magnetic fields, which confine the plasma to rope-like filaments or sheets. This results in the measured non-thermal component of low-frequency radio emission plasma, as well as a plasma $β$ (thermal pressure divided by magnetic pressure) below 1, even in the densest regions. We speculate that all mature HII regions in the CMZ, and galactic nuclei in general, evolve in a magnetically dominated, low plasma $β$ regime. |
| title | The JWST-NIRCam View of Sagittarius C. II. Evidence for Magnetically Dominated HII Regions in the CMZ |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2412.10983 |