Kinematics and electron temperatures in the core of OrionA

A map of the core of OrionA, with a 42′′ resolution in the 64α recombination line of hydrogen, covering ∼5′ by ∼5′, is presented. The Vlsr distribution shows a complex variation about the center of the ionized gas emission: From ∆α=-200′′ to +300′′, the Vlsr varies from -5km s−1 to +2km s−1 then to -4km s−1, finally rising to +3km s−1. A search for cold (Te ∼3000K) ionized gas toward the KL nebula has revealed no measurable differences in Te between this region and other parts of OrionA. The average Te from our data is 8300±200K. We find no significant difference between Te values determined from radio recombination lines and those determined from forbiddenoptical lines of [O III], although theTe value fromBalmer decrement data is markedly lower. The turbulent velocity varies by <5% over the region mapped. On the basis of our 2.45′ resolution, high dynamic range 6 cm continuum map, we find that the emission falls off faster in the East than in theWest. We find support for the model in which OrionA is ionization bounded in the East but density bounded in the West. The ionized gas in the West is flowing in the direction of the Sun, while the more positive Vlsr values in the east may be caused by the flow of ionized gas off the foreground Dark Bay. This ionized region may have little fine scale structure, since there is little continuum emission in interferometer maps.