Figure 3: ζ and σ cloud distribution within the GP. The ratio of λ5797/λ5780 DIB equivalent width is thought to probe the UV radiation field. The σ sightlines, where have W (5797)/W (5780) < 0.3, sample regions with high UV intensity as the λ5797 DIB carrier is suppressed while the λ5780 DIB carrier is enhanced, and typically probe the envelopes of clouds. The ζ sightlines, where W (5797)/W (5780) > 0.3, sample regions where the λ5797 DIB carrier is protected from high energy photons and the λ5780 DIB carrier is suppressed, and typically probe the interiors of clouds (but not the highest densities). As is clear from the map, the LB and the passage towards Loop I are filled with σ clouds due to the harsh environment, but still some small ζ clouds can be found immersed within it.
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