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Title: EVIDENCE FOR H{sub 2} FORMATION DRIVEN DUST GRAIN ALIGNMENT IN IC 63

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{sub 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{sub 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{sub 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{sub 2}. We compare our observations to ab initio modeling based on Radiative Torque Alignment (RAT) theory.
Authors:
; ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ; ;  [6] ;  [7]
  1. SOFIA Science Center, USRA, NASA Ames Research Center, M.S. N211-3 Moffett Field, CA 94035 (United States)
  2. Finnish Centre for Astronomy with ESO, University of Turku, Väisäläntie 20, FI-21500 Piikkiö (Finland)
  3. Institute for Astrophysical Research, Boston University, Boston, MA 02215 (United States)
  4. Observatories of the Carnegie Institution, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
  5. Gemini Observatory, Northern Operations Center, 670 N. A'ohoku Place, Hilo, HI 96720 (United States)
  6. Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706 (United States)
  7. Tuorla Observatory, University of Turku, Väisäläntie 20, FI-21500 Piikkiö (Finland)
Publication Date:
OSTI Identifier:
22270824
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 775; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; ASYMMETRY; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; COSMIC DUST; FLUORESCENCE; FORMATION HEAT; HYDROGEN; INFRARED RADIATION; INTERSTELLAR GRAINS; MOLECULES; NEBULAE; POLARIZATION; STARS; VISIBLE RADIATION