The GBT Diffuse Ionized Gas Survey (GDIGS): Discrete Sources

Abstract

The Green Bank Telescope Diffuse Ionized Gas Survey (GDIGS) traces ionized gas in the Galactic midplane by observing radio recombination line (RRL) emission from 4 to 8 GHz. The nominal survey zone is 32.°3 > ℓ > −5°, ∣ b ∣ < 0.°5. Here, we analyze GDIGS Hn α ionized gas emission toward discrete sources. Using GDIGS data, we identify the velocity of 35 H ii regions that have multiple detected RRL velocity components. We identify and characterize RRL emission from 88 H ii regions that previously lacked measured ionized gas velocities. We also identify and characterize RRL emission from eight locations that appear to be previously unidentified H ii regions and 30 locations of RRL emission that do not appear to be H ii regions based on their lack of mid-infrared emission. This latter group may be a compact component of the Galactic Diffuse Ionized Gas. There are an additional 10 discrete sources that have anomalously high RRL velocities for their locations in the Galactic plane. We compare these objects’ RRL data to ^13 CO, H i, and mid-infrared data, and find that these sources do not have the expected 24 μ m emission characteristic of H ii regions. Based on this comparison we do not think these objects are H ii regions, but we are unable to classify them as a known type of object.

Keywords

• Warm ionized medium
• Interstellar plasma
• H II regions
• Interstellar line emission
• Interstellar medium