| Résumé | The Green Bank Telescope Diffuse Ionized Gas Survey (GDIGS) is a fully sampled radio recombination line (RRL) survey of the inner Galaxy at C-band (4-8 GHz). We average together ~15 Hnα RRLs within the receiver bandpass to improve the spectral signal-to-noise ratio. The average beam size for the RRL observations at these frequencies is ~2'. We grid these data to have spatial and velocity spacings of 30" and 0.5 km, s⁻¹, respectively. Here we discuss the first RRL data from GDIGS: A 6 deg² area surrounding the Galactic H II region complex W43. We attempt to create a map devoid of emission from discrete H II regions and detect RRL emission from the diffuse ionized gas (DIG) across nearly the entire mapped area. We estimate the intensity of the DIG emission by a simple empirical model, taking only the H II region locations, angular sizes, and RRL intensities into account. The DIG emission is predominantly found at two distinct velocities: ~40 and ~100 km s⁻¹. While the 100 km s⁻¹ component is associated with W43 at a distance of ~6 kpc, the origin of the 40 km s⁻¹ component is less clear. Since the distribution of the 40 km s⁻¹ emission cannot be adequately explained by ionizing sources at the same velocity, we hypothesize that the plasma at the two velocity components is interacting, placing the 40 km s⁻¹ DIG at a similar distance as the 100 km s⁻¹ emission. We find a correlation between dust temperature and integrated RRL intensity, suggesting that the same radiation field that heats the dust also maintains the ionization of the DIG. |
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