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2013ApJ...775...84A
Evidence for H<SUB>2</SUB> Formation Driven Dust Grain Alignment in IC 63
Andersson, B. -G. ( SOFIA Science Center, USRA, NASA Ames Research Center, M.S. N211-3 Moffett Field, CA 94035, USA ); Piirola, V. ( Finnish Centre for Astronomy with ESO, University of Turku, Väisäläntie 20, FI-21500 Piikkiö, Finland ); De Buizer, J. ( SOFIA Science Center, USRA, NASA Ames Research Center, M.S. N211-3 Moffett Field, CA 94035, USA ); Clemens, D. P. ( Institute for Astrophysical Research, Boston University, Boston, MA 02215, USA ); Uomoto, A. ( Observatories of the Carnegie Institution, 813 Santa Barbara Street, Pasadena, CA 91101, USA ); Charcos-Llorens, M. ( SOFIA Science Center, USRA, NASA Ames Research Center, M.S. N211-3 Moffett Field, CA 94035, USA ); Geballe, T. R. ( Gemini Observatory, Northern Operations Center, 670 N. A'ohoku Place, Hilo, HI 96720, USA ); Lazarian, A. ( Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706, USA ); Hoang, T. ( Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706, USA ); Vornanen, T. ( Tuorla Observatory, University of Turku, Väisäläntie 20, FI-21500 Piikkiö, Finland ) show affiliations
The Astrophysical Journal, Volume 775, Issue 2, article id. 84, 16 pp. (2013).
Published in Oct 2013
In the interstellar medium (ISM), molecular hydrogen is expected to form almost exclusively on the surfaces of dust grains. Due to that molecule's large formation energy (-4.5 eV), several dynamical effects are likely associated with the process, including the alignment of asymmetric dust grains with the ambient magnetic field. Such aligned dust grains are, in turn, believed to cause the broadband optical/infrared polarization observed in the ISM. Here, we present the first observational evidence for grain alignment driven by H2 formation, by showing that the polarization of the light from stars behind the reflection nebula IC 63 appears to correlate with the intensity of H2 fluorescence. While our results strongly suggest a role for "Purcell rockets" in grain alignment, additional observations are needed to conclusively confirm their role. By showing a direct connection between H2 formation and a probe of the dust characteristics, these results also provide one of the first direct confirmations of the grain-surface formation of H2. We compare our observations to ab initio modeling based on Radiative Torque Alignment (RAT) theory.
Keywords:
Free Keywords: ISM: individual objects: IC 63; ISM: magnetic fields; dust; extinction; polarization
Astronomy: ISM: individual objects: IC 63; ISM: magnetic fields; dust; extinction; polarization
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