The three dimensional dynamic structure of the inner Orion Nebula

Abstract

The three dimensional structure of the brightest part of the Orion Nebula is assessed in the light of published and new data. We find that the widely accepted model of a concave blister of ionized material needs to be altered in the southwest direction from the Trapezium, where we find that the Orion-S feature is a separate cloud of very optically thick molecules within the body of ionized gas, which is probably the location of the multiple embedded sources that produce the outflows that define the Orion-S star formation region. Evidence for this cloud comes from the presence of H2CO lines in absorption in the radio continuum and discrepancies in the extinction derived from radio-optical and optical only emission. We present an equilibrium Cloudy model of the Orion-S cloud, which successfully reproduces many observed properties of this feature. We also report the discovery of an open-sided shell of [O III] surrounding the Trapezium stars, revealed through emission line ratio images and the onset of radiation shadows beyond some proplyds. We show that the observed properties of the shell are consistent with it being a stationary structure, produced by shock interactions between the ambient nebular gas and the high-velocity wind from theta^1 Ori C. We examine the implications of the recently published evidence for a large blueshifted velocity of theta^1 Ori C with respect to the Orion Molecular Cloud, which could mean that this star has only recently begun to photoionize the Orion Nebula. We show that current observations of the Nebula do not rule out such a possibility, so long as the ionization front has propagated into a pre-existing low-density region. In addition, a young age for the Nebula would help explain the presence of nearby proplyds with a short mass-loss timescale to photoablation.

AJ in press, 18 pages, 7 figures (2 in full color)

References in corpus (13)

• Kinematic Structure of the Orion Nebula Cluster and its Surroundings
• Million-Degree Plasma Pervading the Extended Orion Nebula
• Visual Binaries in the Orion Nebula Cluster
• Monitoring the Large Proper Motions of Radio Sources in the Orion BN/KL Region
• Visual/infrared interferometry of Orion Trapezium stars: Preliminary dynamical orbit and aperture synthesis imaging of the Theta 1 Orionis C system
• The magnetic field and confined wind of the O star ${\theta }^1$~Orionis~C
• Sensitivity of PDR Calculations to Microphysical Details
• Silicon Monoxide Observations Reveal a Cluster of Hidden Compact Outflows in the OMC1 South Region
• High Velocity Features in the Orion Nebula
• Long-term monitoring of theta1 OriC: the spectroscopic orbit and an improved rotational period
• Small scale behavior of the physical conditions and the abundance discrepancy in the Orion nebula
• Large Scale Flows from Orion-South
• Optical interferometric observations of Theta 1 Orionis C from NPOI and implications for the system orbit

Cited by in corpus (2)

• A New Class of Nascent Eclipsing Binaries with Extreme Mass Ratios
• Dramatic Evolution of the Disk-Shaped Secondary in the Orion Trapezium Star Theta1 Ori B1 (BM Ori): MOST Satellite Observations