Radio Recombination Lines at Thirty Years

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Session 27 -- Hat Creek
Oral presentation, Tuesday, 8:30-12:30, Dwinelle 155 Room

[27.03] Radio Recombination Lines at Thirty Years

W. M. Goss (NRAO)

The discovery of radio recombination lines (RRL) in the early 1960's coincided with the early years of the Hat Creek Telescope. A major galactic survey of 46 sources was carried out by Nan Dieter and published in 1967 (ApJ, Vol. 150, p. 435). Dieter's work showed how RRL could be used to investigate the physical conditions of HII regions and to study galactic kinematics.

After almost 30 years of research, the sensitivity and resolution of RRL investigations have progressed dramatically. I will summarize recent VLA research with angular resolutions of a few arc sec and sensitivities of about 0.1 mJy/beam. Examples are an H92 alpha survey of Sgr A West (Roberts and Goss), an He92 alpha survey in W3 (Wood, Benaglia, et al.) which shows anomalous helium lines and H lines with large line widths ($>$ 100 kms$^{-1}$) in G25.5+0.2 (Subrahmanyan, et al.), Sgr B2 (Gaume, et al.) and NGC 7538 (Benaglia, et al.). Finally, using the VLA, RRLs have been discovered in 5 extragalactic systems by Zhao, Anantharamaiah, et al.

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