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Radio studies of the Galactic center. I - The Sagittarius A complex
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The Sagittarius A Complex is a prominent radio source at the Galactic center. The study combines VLA observations at 90 cm, 20 cm, and 6 cm to derive spectral‑index and optical‑depth maps that constrain the three‑dimensional structure of the complex. At 90 cm the thermal Sgr A West is seen in absorption against the nonthermal Sgr A East, proving it lies in front; the Sgr A East shell shows a low‑frequency turnover (optical depth 1–2) from free‑free absorption (emission measure ≈10⁵ pc cm⁻⁶ at T_e≈5000 K), and the surrounding halo also turns over, indicating a mix of thermal and nonthermal gas with the thermal component responsible for the absorption across Sgr A East. Publication: The Astrophysical Journal, July 1989, DOI 10.1086/167635.
view Abstract Citations (161) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radio Studies of the Galactic Center. I. The Sagittarius A Complex Pedlar, A. ; Anantharamaiah, K. R. ; Ekers, R. D. ; Goss, W. M. ; van Gorkom, J. H. ; Schwarz, U. J. ; Zhao, Jun-Hui Abstract VLA observations of the Sgr A complex at 90 cm, 20 cm, and 6 cm are combined to obtain spectral index and optical depth distributions across the source and are used to constrain the three-dimensional structure at the Galactic center. At 90 cm the 'spiral' structure of the thermal source Sgr A West is clearly seen in absorption against the nonthermal emission of Sgr A East, showing conclusively that the former is in front of the latter. The entire shell of Sgr A East shows a low-frequency turnover corresponding to an optical depth of 1-2. This turnover corresponds to free-free absorption with an emission measure of about 100,000 pc/cm exp 6 if the electron temperature is about 5000 K. The approximately 7 arcmin halo surrounding Sgr A East and West also shows a low-frequency turnover. It is suggested that the halo contains a mixture of thermal and nonthermal gas and that the thermal component is responsible for the absorption extending across Sgr A East. Publication: The Astrophysical Journal Pub Date: July 1989 DOI: 10.1086/167635 Bibcode: 1989ApJ...342..769P Keywords: Centimeter Waves; Galactic Nuclei; Galactic Structure; Milky Way Galaxy; Radio Astronomy; Active Galactic Nuclei; Sagittarius Constellation; Star Formation; Supernovae; Very Large Array (Vla); Astrophysics; GALAXIES: NUCLEI; GALAXIES: THE GALAXY; INTERFEROMETRY full text sources ADS | data products SIMBAD (7) Related Materials (1) Part 2: 1991MNRAS.249..262A