Figure 2.

Color-composite visible image of the Orion Nebula (M42) taken with the ACS instrument on board the Hubble Space Telescope (HST). The assigned colors are: red and orange for [S ii] and Hα, blue for B, and green for V filters respectively (Robberto et al. 2013). (Left): Green contours show the integrated intensity (W) of the H41α recombination line (from 3 to 21 K km s⁻¹ in steps of 2 K km s⁻¹). The white dotted 200″ (0.4 pc) radius circle is centered on θ¹ Ori C, the brightest star of the Trapezium. We define the “extended cloud face” component to lie outside this circle. Middle: Black contours show the total [C ii] 158 μm integrated intensity (v_LSR=−30 to +30 km s⁻¹ with W from 0 to 1300 K km s⁻¹ in steps of 150 K km s⁻¹). Right: [C ii] “blue-shifted streamer” (emission from v_LSR=−2 to +5 km ⁻¹) with W from 0 to 60 K km s¹ (cyan) and from 80 to 140 K km s¹ (blue), all in steps of 20 K km s⁻¹. This emission coincides with the Northern dark lane and with the Dark bay seen in visible-light images of the Nebula. The Orion hot core in the BN/KL region and Orion S positions are indicated by red and blue stars respectively. The positions where line spectra have been extracted (shown in Figure 3) are indicated by cyan squares.