CO-Line and Radio Continuum Study of Elephant Trunks: The Pillars of Creation in M16

Abstract

Molecular-line and radio continuum properties of the elephant trunks (ET, pillars of creation) in M16 are investigated by analyzing the 12CO(J=1-0), 13CO(J=1-0) and C18O(J=1-0)-line survey data with the Nobeyama 45-m telescope and the Galactic plane radio survey at 20 and 90 cm with the Very Large Array. The head clump of Pillar West I is found to be the brightest radio source in M16, showing thermal spectrum and property of a compact HII region with the nearest O5 star in NGC 6611 being the heating source. The radio pillars have cometary structure concave to the molecular trunk head, and the surface brightness distribution obeys a simple illumination law by a remote excitation source. The molecular density in the pillar head is estimated to be several $10^4$ H$_2$ cm$^{-3}$ and molecular mass $\sim 13-40 M\odot$. CO-line kinematics reveals random rotation of the clumps in the pillar tail at $\sim 1-2$ km/s, comparable to the velocity dispersion and estimated Alfven velocity. It is suggested that the random directions of velocity gradients would manifest a torsional magnetic oscillation of the clumps around the pillar axis.