Horsehead Nebula and the IC 434 I-front

Illustration showing the likely configuration of the Horsehead Nebula and the IC 434 I-front. Our line of sight is from below and in front of the figure. σ Ori is located about 4 pc to the right and slightly behind the plane of the sky from our vantage point. The thin solid line shows the I-front, with cyan vectors indicating the approximate direction of the ionized photoablation flow. The thick solid line shows the approximate location where CO is dissociated into C I and O I. Most [C II] emission is located between this line and the I-front. The thick dashed line indicates the likely location of the D-type shock or compression wave pushed into the Orion B cloud on the left. The black dotted regions are meant to indicate preexisting dense clumps in the cloud and the compressed layer between the advancing H II region driven D-type shock or compression wave.

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