Coherence in Dense Cores

 

Summary: In the series of papers listed below, we show that "dense cores" of gas in the interstellar medium which form stars like our Sun can be thought of as "Islands of Calm in a Turbulent Sea."

It has been known for some time that these dense cores have nearly thermal line widths, and that the medium around them has highly non-thermal line widths. These papers are about the transition from the non-thermal (self-similar, fractal, turbulent) regime to the almost-thermal ("coherent") regime.

Paper I: "Coherence in Dense Cores. I. NH3 Observations," (J. Barranco & A. Goodman ) presents very high-senistivity NH3 mapping of low-mass star-forming dense cores. The mapping data show that spectral line width does not increase with size scale inside these cores, and we conclude that the cores exhibit velocity coherence, as opposed to the more turbulent behavior which characterizes the larger-scale clouds which surrounds the cores.

Paper II: "Coherence in Dense Cores. II. The Transition to Coherence," (A. Goodman, J. Barranco, D. Wilner & M. Heyer). Maps of the environs of the cores studied in Paper I show line width increasing with size. The point where line width levels off is identified as the "transition to coherence."

Highlights of the Papers Include:

  1. Demonstration that velocity dispersion is nearly constant inside low-mass cores.
  2. Arguments that the gas filling factor inside cores is much higher than in their surroundings.
  3. Discussion of the cause of this "transition to coherence," favoring a scenario where dissipation imposes an inner scale on a magnetized turbulent cascade.
  4. Definition of Four Distinct Types of Line Width-Size Relations, and discussion of the important physical distinctions among them.

A description of recent work on this project is also available in a recent observing proposal to IRAM. (Click here for: PDF file of text, Figure 1)

Current observations are described and analyzed at our "Coherent Dense Cores Collaboration Page."

Credits:

Most of the NH3 observations used in these papers were carried out at the Haystack Observatory, in Westford, MA. The C18O observations are from the UMASS/Five College Radio Astronomy Observatory in Amherst, MA. The OH observations in Paper II are from the NAIC Arecibo Observatory in Arecibo, PR.

Please E-mail Alyssa Goodman for information beyond what's available here.

Last Update: November 1999