Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-09-04
Astrophys.J.596:L239-L242,2003
Astronomy and Astrophysics
Astrophysics
11 pages, 4 figures, accepted for publication in ApJL (Oct 20, 2003)
Scientific paper
10.1086/379502
It has been suggested that under average interstellar field strengths the cyclotron interaction between ions and magnetic fields is strong enough to narrow the linewidth and suppress the line wings in the ion spectra. We present evidence for the cyclotron interaction effect at arcsec scale on the velocity dispersions in the spectra of ion/neutral molecular species in DR21(OH) observed with the OVRO-MMA. Using a spatial resolution $\sim$ 3 times higher than previous CSO observations by Houde et al. (2002), we show that H$^{13}$CO$^+$ and H$^{13}$CN are coexistent at the scale of our observations (6\arcsec). In the eastern parts of the DR21(OH) core where the dynamics is simple, the ion linewidths are indeed narrower than the neutral linewidths with an average ion-to-neutral linewidth ratio of 0.82$\pm$0.04. We use our results, along with the existing Zeeman and dust/CO polarization data on small scales, to derive the 3-D magnetic field structure. We obtain a field strength of $0.44\pm$0.12 mG with inclination of 36\deg to the line of sight, directed toward the observer, and a position angle of $-$75\deg in the plane of the sky. With the full magnetic field strength derived here, we are able to conclude that the MM1 core of DR21(OH) is magnetically supercritical; although turbulence provides the dominant support.
Lai Shih-Ping
Langer William D.
Velusamy Thangasamy
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