Extended Data Fig. 4: HI spectra toward DR21.
From: Ionized carbon as a tracer of the assembly of interstellar clouds
a, The HI absorption spectrum is shown in black, the 100 colored spectra represent the HI emission within a square of \(2{0}^{{\prime} }\times 2{0}^{{\prime} }\) around DR21 in a grid of \({1}^{{\prime} }\). b, The black curve is again the absorption HI spectrum toward DR21, the blue curve is the HI emission spectrum (off), and the orange curve shows the Gaussian fit to the blue off spectrum.
