Expanding bubbles in Orion A: [C _II] observations of M42, M43, and NGC 1977

The Orion Molecular Cloud is the nearest massive-star forming region. Massive stars have profound effects on their environment due to their strong radiation fields and stellar winds. Stellar feedback is one of the most crucial cosmological parameters that determine the properties and evolution of the interstellar medium in galaxies.

We aim to understand the role that feedback by stellar winds and radiation play in the evolution of the interstellar medium. Velocity-resolved observations of the [C _II] 158microm fine-structure line allow us to study the kinematics of UV-illuminated gas. Here, we present a square-degree-sized map of [C _II] emission from the Orion Nebula complex at a spatial resolution of 16″ and high spectral resolution of 0.2kms^-1, covering the entire Orion Nebula (M42) plus M43 and the nebulae NGC 1973, 1975, and 1977 to the north. We compare the stellar characteristics of these three regions with the kinematics of the expanding bubbles surrounding them.

We use [C ^II] 158microm line observations over an area of 1.2deg² in the Orion Nebula complex obtained by the upGREAT instrument onboard SOFIA.

The bubble blown by the O7V star θ ¹ Ori C in the Orion Nebula expands rapidly, at 13kms^-1. Simple analytical models reproduce the characteristics of the hot interior gas and the neutral shell of this wind-blown bubble and give us an estimate of the expansion time of 0.2 Myr. M43 with the B0.5V star NU Ori also exhibits an expanding bubble structure, with an expansion velocity of 6kms^-1. Comparison with analytical models for the pressure-driven expansion of H _II regions gives an age estimate of 0.02 Myr. The bubble surrounding NGC 1973, 1975, and 1977 with the central B1V star 42 Orionis expands at 1.5kms^-1, likely due to the over-pressurized ionized gas as in the case of M43. We derive an age of 0.4 Myr for this structure.

We conclude that the bubble of the Orion Nebula is driven by the mechanical energy input by the strong stellar wind from θ ¹ Ori C, while the bubbles associated with M43 and NGC 1977 are caused by the thermal expansion of the gas ionized by their central later-type massive stars.