Sensitive Observations of Radio Recombination Lines in Orion and W51: The Data and Detection of Systematic Recombination Line Blueshifts Proportional to Impact Broadening

Abstract

Sensitive spectral observations made in two frequency bands near 6.0 and 17.6 GHz are described for Orion and W51. Using frequency switching we were able to achieve a dynamic range in excess of 10,000 without fitting sinusoidal or polynomial baselines. This enabled us to detect lines as weak as T${}_{A}1mKinthesestrongcontinuumsources.Hydrogenrecombinationlineswith$Δn$ as high as 25 have been detected in Orion. In the Orion data, where the lines are stronger, we have also detected a systematic shift in the line center frequencies proportional to linewidth that cannot be explained by normal optical depth effects.

22 pages, 13 figures. Accepted for publication in Astrophysics and Space Science

Cited by in corpus (5)

• A 1.3 cm Line Survey toward Orion KL
• Ionization Profiles of Galactic HII Regions
• On the Ionization of Luminous WMAP Sources in the Galaxy : Constraints from He Recombination Line Observations with the GBT
• On The Apparent Narrowing of Radio Recombination Lines at High Principal Quantum Numbers
• New Clues to the Impact Broadening Mystery in Radio Recombination Lines