A1 Refereed original research article in a scientific journal
Evidence for H2 Formation Driven Dust Grain Alignment in IC 63
Authors: B-G Andersson, V Piirola, J De Buizer, D P Clemens, A Uomoto, M Charcos-Llorens, T R Geballe, A Lazarian, T Hoang, T Vornanen
Publisher: IOP PUBLISHING LTD
Publishing place: BRISTOL; TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND
Publication year: 2013
Journal: Astrophysical Journal
Journal name in source: Astrophysical Journal
Journal acronym: Astrophys.J.
Number in series: 2
Volume: 775
Issue: 2
First page : 84
Last page: 84
Number of pages: 16
ISSN: 0004-637X
DOI: https://doi.org/10.1088/0004-637X/775/2/84(external)
Abstract
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 H-2 formation, by showing that the polarization of the light from stars behind the reflection nebula IC 63 appears to correlate with the intensity of H-2 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 H-2 formation and a probe of the dust characteristics, these results also provide one of the first direct confirmations of the grain-surface formation of H-2. We compare our observations to ab initio modeling based on Radiative Torque Alignment (RAT) theory.
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 H-2 formation, by showing that the polarization of the light from stars behind the reflection nebula IC 63 appears to correlate with the intensity of H-2 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 H-2 formation and a probe of the dust characteristics, these results also provide one of the first direct confirmations of the grain-surface formation of H-2. We compare our observations to ab initio modeling based on Radiative Torque Alignment (RAT) theory.
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