Radio recombination lines toward the galactic center lobe

C. J. Law, D. Backer, F. Yusef-Zadeh, R. Maddalena

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


The Galactic center (GC) lobe is a degree-tall shell seen in radio continuum images of the GC region. If it is actually located in the GC region, formation models would require massive energy input (e.g., starburst or jet) to create it. At present, observations have not strongly constrained the location or physical conditions of the GC lobe. This paper describes the analysis of new and archival single-dish observations of radio recombination lines toward this enigmatic object. The observations find that the ionized gas has a morphology similar to the radio continuum emission, suggesting that they are associated. We study averages of several transitions from H106α to H191ϵ and find that the line ratios are most consistent with gas in local thermodynamic equilibrium. The radio recombination line widths are remarkably narrow, constraining the typical electron temperature to be less than about 4000 K. These observations also find evidence of pressure broadening in the higher electronic states, implying a gas density of ne = 910+310-450 cm-3. The electron temperature, gas pressure, and morphology are all consistent with the idea that the GC lobe is located in the GC region. If so, the ionized gas appears to form a shell surrounding the central 100 parsecs of the galaxy with a mass of roughly 105 MȮ, similar to ionized outflows seen in dwarf starbursts.

Original languageEnglish (US)
Pages (from-to)1070-1081
Number of pages12
JournalAstrophysical Journal
Issue number2
StatePublished - 2009


  • Galaxy: center
  • Radio lines: General

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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