A dense molecular ring surrounding the nonthermal galactic center radio shell G359.1-0.5

Keven I. Uchida*, Mark Morris, J. Bally, M. Pound, F. Yusef-Zadeh

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Scopus citations


A new 12CO survey of the Galactic center region reveals a nearly continuous ring of molecular gas that is centered on and concentric with the nonthermal radio continuum shell G359.1-0.5. The molecular feature has high radial velocities, between -60 and -190 km s-1, indicating that it is likely to be located at the distance of the Galactic center ; its diameter is then about 75 pc. The mass of the ring, based on its integrated CO line emission, is about 2.5 × 106 M⊙. We hypothesize that the expansion of the CO ring was initiated by the winds, radiation, and supernova ejecta from a massive central cluster of O-type stars. Some evidence for a central star cluster is provided by VLA radio continuum observations which show a cluster of point radio sources near the center of remnant G359.1-0.5. If the CO ring is as close to the Galactic center as it appears in projection (which we believe to be the case) then a velocity difference of about 100 km s-1 between its eastern and western edges (in the Galactic coordinate frame) might in large part be the result of shear motions in the Galactic center region. In support of our shear hypothesis, a computer code has been written to model the expansion of a mass-accumulating shell in a differentially rotating medium. We find that a superbubble generated by ∼ 200 O-type stars, under conditions observed in the Galactic center region, compares both kinematically and morphologically with the observed molecular feature. If, however, the CO ring is much farther from the Galactic center (> 1 kpc) than it appears, then the effects of shear will be reduced. Under these circumstances, much or all of the observed velocity difference between the edges of the ring might be attributed to expansion. The expansion energy of the ring will then be large, at least 6 × 1052 ergs, requiring the combined winds and radiation from many hundreds of O-type stars and their subsequent supernova explosions as a central energy source.

Original languageEnglish (US)
Pages (from-to)128-138
Number of pages11
JournalAstrophysical Journal
Issue number1
StatePublished - 1992


  • Galaxy: center
  • ISM: individual (G359.1 -0.5)
  • ISM: molecules

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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