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Cited by 144Astrophysical Phenomena and ObservationsStellar, planetary, and galactic studiesAstrophysics and Star Formation Studies

DYNAMICS OF IONIZED GAS AT THE GALACTIC CENTER: VERY LARGE ARRAY OBSERVATIONS OF THE THREE-DIMENSIONAL VELOCITY FIELD AND LOCATION OF THE IONIZED STREAMS IN SAGITTARIUS A WEST

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Zhao, Jun-Hui, Morris, Mark R., Goss, W. M., An, Tao·2009·The Astrophysical Journal
DOI 10.1088/0004-637x/699/1/186
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Abstract

We present new results based on high-resolution observations of Sgr A West at the Galactic center with the Very Large Array (VLA) at 1.3 cm. By combining recent observations with those made at earlier epochs with the VLA at wavelengths of 1.3 and 3.6 cm, we measured proper motions for 71 compact H ii components in the central 80'' (3 pc, assuming D = 8 pc). Using VLA archival data for the H92α radio recombination line, we also investigated radial velocities in the LSR velocity range from +200 to −415 km s −1 . Combining proper motion and radial velocity measurements, we have determined the three-dimensional velocity distribution in Sgr A West. We find that the three ionized streams (Northern Arm, Eastern Arm, and Western Arc) in the central 3 pc can be modeled with three bundles of Keplerian orbits around Sgr A*. Assuming that each of the observed streams of ionized gas follows a single orbit, we determined the five orbital parameters ( a , e , Ω, ω, i ) for each of them using least-square fitting to the loci of the streams. The degeneracy in the orbital solutions for both the direction of flow and the two mirror images can be further resolved using the information obtained from the velocity measurements. Our results confirm earlier results on the streams in the Western Arc and the Northern Arm to be in Keplerian orbits, suggesting that the stream in the Eastern Arm is also consistent with an elliptical orbit. All three are confined within the central 3 pc. Both the Northern and Eastern Arm streams have high eccentricities ( e = 0.83 ± 0.10 and 0.82 ± 0.05, respectively), while the Western Arc stream is nearly circular, with e = 0.2 ± 0.15. All three streams orbit around Sgr A* in a counterclockwise sense (viewed from the Earth) and have orbital periods in the range 4–8 × 10 4 yr. To verify the fit, the distributions of radial and transverse velocity vectors in Sgr A West were also computed using the Keplerian model and they show good agreement with both the proper motion and radial velocity data. In addition, the computed orbits suggest that the Northern and Eastern Arm streams may collide in the "Bar" region (a few arcsec south of Sgr A*) and that most of the orbiting ionized gas in the "Bar" region is located behind Sgr A*. We also report an ionized nebula associated with IRS 8, including a bow shock in radio continuum emission which shows excellent agreement with near infrared observations. From the H92α line data, we find evidence of substantial interaction between the IRS 8 nebula and the Northern Arm stream occurring in the bow-shock region. Other new morphological features revealed in our high-resolution image include (1) a helical structure in the Northern Arm, suggesting that MHD plays an important role in the motion of the ionized gas, in addition to the dynamics determined by the central gravitational field, and (2) a linear feature in the IRS 16 region, suggesting that the compressed edge of the Northern Arm may result from the collective winds and radiation pressure from the high mass stars in the IRS16 cluster.

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  • The CND (inclination ≈70°) and ionized streams (inclination ≈50°) are significantly misaligned with the large scale Galactic plane (inclination=90°).

    “The CND(inclination ≈ 70 ◦ ) and ionized streams (inclination ≈ 50 ◦ ) are significantly misaligned with the large scale Galactic plane (inclination = 90 ◦ ) (Jackson et al. 1993; Paumard et al. 2004; Zhao et al. 2009; Genzel et al. 2010), an important issue I will come back to below.”

    From The Fermi/eROSITA bubbles: a look into the nuclear outflow from the Milky Way (2024) · cites this paper as Zhao et al. 2009

    Section 5.1 (page unavailable) gives fitted inclinations of 139° ± 10°, 122° ± 5°, and 117° ± 3° for the three ionized streams. Their complementary angles are roughly 41°–63°, consistent with a loose description of the streams as inclined by about 50°, but the paper uses a different angle convention. The passages found do not establish the CND’s ≈70° inclination or state the Galactic-plane comparison. (LLM, conf=0.84)

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Research works printed but not linked: 2

  1. Tanner, A., Ghez, A. M., Morris, M. R., & Christou, J. C. 2005, ApJ, 620, 744 · DOI
  2. Zhao, J.-H., & Goss, W. M 1999, in ASP Conf. Ser. 186, The Central Parsecs of the Galaxy, ed. H. Falcke, A. Cotera, W. J. Duschl, F. Melia, & M. J. Rieke (San Francisco, CA: ASP), 224

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Authors
Zhao, J.-H., Morris, M. R., Goss, W. M., & An, T.
Affiliations
  • Center for Astrophysics Harvard & Smithsonian (US)
  • University of California, Los Angeles (US)
  • National Radio Astronomy Observatory (US)
  • Chinese Academy of Sciences (CN)
Corresponding author
Zhao, Jun-Hui
ORCID
Venue
The Astrophysical Journal
Publisher
American Astronomical Society
Published
2009-06-10
Volume
699
Issue
1
Pages
186-214
ISSN
  • 0004-637X (ISSN-L)
  • 1538-4357
DOI
10.1088/0004-637x/699/1/186
OpenAlex
W2156835784
Cited by
144
References
66
Citations by year
2026: 9 · 2025: 5 · 2024: 4 · 2023: 10 · 2022: 3 · 2021: 5 · 2020: 10 · 2019: 10 · 2018: 9 · 2017: 10 · 2016: 9 · 2015: 11 · 2014: 6 · 2013: 18 · 2012: 12
FWCI
4.20
Type
journal article
Language
en
Open access
Locations
  • The Astrophysical Journal (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • arXiv (Cornell University)
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysical Phenomena and Observations
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Stellar, planetary, and galactic studies
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysics and Star Formation Studies
Keywords
Sgr A West, Sgr A*, Keplerian orbits, orbital elements, proper motions, radial velocity, H II regions, three-dimensional velocity field, orbital eccentricity, orbital period, galactic bars

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