The GBT Diffuse Ionized Gas Survey: Tracing the Diffuse Ionized Gas around the Giant Hii Region W43
Abstract
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 $\mathrm{km}\,{{\rm{s}}}^{-1}$ , 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 $\mathrm{km}\,{{\rm{s}}}^{-1}$ . While the 100 $\mathrm{km}\,{{\rm{s}}}^{-1}$ component is associated with W43 at a distance of ∼6 kpc, the origin of the 40 $\mathrm{km}\,{{\rm{s}}}^{-1}$ component is less clear. Since the distribution of the 40 $\mathrm{km}\,{{\rm{s}}}^{-1}$ 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 $\mathrm{km}\,{{\rm{s}}}^{-1}$ DIG at a similar distance as the 100 $\mathrm{km}\,{{\rm{s}}}^{-1}$ 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2020
- DOI:
- 10.3847/1538-4357/ab643e
- arXiv:
- arXiv:1912.08657
- Bibcode:
- 2020ApJ...889...96L
- Keywords:
-
- Interstellar medium;
- Galactic radio sources;
- Radio astronomy;
- Interstellar abundances;
- H II regions;
- Warm ionized medium;
- Surveys;
- Photodissociation regions;
- 847;
- 571;
- 1338;
- 832;
- 694;
- 1788;
- 1671;
- 1223;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 17 pages, 12 figures, 1 table. Accepted for publication in ApJ