AN IMPRINT OF MOLECULAR CLOUD MAGNETIZATION IN THE MORPHOLOGY OF THE DUST POLARIZED EMISSION

We describe a morphological imprint of magnetization found when considering the relative orientation of the magnetic field direction with respect to the density structures in simulated turbulent molecular clouds. This imprint was found using the Histogram of Relative Orientations (HRO), a new technique that utilizes the gradient to characterize the directionality of density and column density structures on multiple scales. We present results of the HRO analysis in three models of molecular clouds in which the initial magnetic field strength is varied, but an identical initial turbulent velocity field is introduced, which subsequently decays. The HRO analysis was applied to the simulated data cubes and mock-observations of the simulations produced by integrating the data cube along particular lines of sight. In the three-dimensional analysis we describe the relative orientation of the magnetic field B with respect to the density structures, showing that: (1) the magnetic field shows a preferential orientation parallel to most of the density structures in the three simulated cubes, (2) the relative orientation changes from parallel to perpendicular in regions with density over a critical density nT in the highest magnetization case, and (3) the change of relative orientation is largest for the highest magnetization and decreases in lower magnetization cases. This change in the relative orientation is also present in the projected maps. In conjunction with simulations, HROs can be used to establish a link between the observed morphology in polarization maps and the physics included in simulations of molecular clouds.

[1]  Zhi-Yun Li,et al.  Magnetically Regulated Star Formation in Three Dimensions: The Case of the Taurus Molecular Cloud Complex , 2008, 0804.4201.

[2]  A. Lazarian,et al.  Radiative torques: analytical model and basic properties , 2007, 0707.0886.

[3]  M. Houde,et al.  MAGNETIC FIELDS AND INFALL MOTIONS IN NGC 1333 IRAS 4 , 2009, 0907.1301.

[4]  Alyssa A. Goodman,et al.  Optical polarization maps of star-forming regions in Perseus, Taurus, and Ophiuchus , 1990 .

[5]  M. L. Norman,et al.  Magnetic field diagnostics based on far-infrared polarimetry: tests using numerical simulations , 2001 .

[6]  L. Mundy,et al.  MISALIGNMENT OF MAGNETIC FIELDS AND OUTFLOWS IN PROTOSTELLAR CORES , 2012, 1212.0540.

[7]  R. Larson.  Turbulence and star formation in molecular clouds , 1980 .

[8]  B. T. Draine,et al.  Radiative Torques on Interstellar Grains. III. Dynamics with Thermal Relaxation , 2002 .

[9]  P. Koch,et al.  MAGNETIC FIELD STRENGTH MAPS FOR MOLECULAR CLOUDS: A NEW METHOD BASED ON A POLARIZATION–INTENSITY GRADIENT RELATION , 2012, 1201.4263.

[10]  P. Hennebelle,et al.  Molecular cloud evolution – IV. Magnetic fields, ambipolar diffusion and the star formation efficiency , 2011, 1101.3384.

[11]  A. Goodman,et al.  THE ANGULAR MOMENTUM OF MAGNETIZED MOLECULAR CLOUD CORES: A TWO-DIMENSIONAL–THREE-DIMENSIONAL COMPARISON , 2010, 1003.5118.

[12]  E. Ostriker,et al.  Theory of Star Formation , 2007, 0707.3514.

[13]  A. Banday,et al.  Modelling the Galactic magnetic field on the plane in two dimensions , 2009, 0907.3994.

[14]  Richard M. Crutcher,et al.  Detection of the CN Zeeman Effect in Molecular Clouds , 1999 .

[15]  A. Boss,et al.  Protostars and Planets VI , 2000 .

[16]  Richard A. Young,et al.  SIMULATION OF HUMAN RETINAL FUNCTION WITH THE GAUSSIAN DERIVATIVE MODEL. , 1986 .

[17]  P. Koch,et al.  DUST CONTINUUM AND POLARIZATION FROM ENVELOPE TO CORES IN STAR FORMATION: A CASE STUDY IN THE W51 NORTH REGION , 2012, 1212.0656.

[18]  R. Teyssier.  Cosmological hydrodynamics with adaptive mesh refinement - A new high resolution code called RAMSES , 2001, astro-ph/0111367.

[19]  S. Masi,et al.  First detection of polarization of the submillimetre diffuse galactic dust emission by Archeops , 2003, astro-ph/0306222.

[20]  B. Draine,et al.  Infrared extinction and polarization due to partially aligned spheroidal grains: Models for the dust toward the BN object , 1985 .

[21]  R. Teyssier,et al.  A high order Godunov scheme with constrained transport and adaptive mesh refinement for astrophysical magnetohydrodynamics , 2006 .

[22]  R. Klessen,et al.  Accretion-driven turbulence as universal process: galaxies, molecular clouds, and protostellar disks , 2009, 0912.0288.

[23]  J. Scalo,et al.  On the Probability Density Function of Galactic Gas. I. Numerical Simulations and the Significance of the Polytropic Index , 1997, astro-ph/9710075.

[24]  J. Weingartner,et al.  Radiative Torques on Interstellar Grains. II. Grain Alignment , 1996, astro-ph/9611149.

[25]  A. Goodman,et al.  ANCHORING MAGNETIC FIELD IN TURBULENT MOLECULAR CLOUDS , 2009, 0908.1549.

[26]  B. T. Draine,et al.  Radiative Torques on Interstellar Grains: I. Superthermal Spinup , 1996 .

[27]  R. Klessen,et al.  The link between molecular cloud structure and turbulence , 2010, 1001.2453.

[28]  M. Tamura,et al.  NEAR-INFRARED-IMAGING POLARIMETRY TOWARD SERPENS SOUTH: REVEALING THE IMPORTANCE OF THE MAGNETIC FIELD , 2011, 1104.2977.

[29]  A. Chepurnov,et al.  Polarization of Dust Emission in Clumpy Molecular Clouds and Cores , 2006, astro-ph/0611324.

[30]  Ralf Klessen,et al.  Clump morphology and evolution in MHD simulations of molecular cloud formation , 2008, 0808.0986.

[31]  P. Kronberg,et al.  Rotation measures and the galactic magnetic field. , 1980 .

[32]  N. Peretto,et al.  The Pipe Nebula as seen with Herschel: formation of filamentary structures by large-scale compression? , 2012, 1203.3403.

[33]  Enrico Fermi,et al.  Magnetic fields in spiral arms , 1953 .

[34]  Brazil,et al.  Polarimetry toward the IRAS Vela Shell. II. Extinction and Magnetic Fields , 2007, astro-ph/0702550.

[35]  M. Juvela,et al.  The Power Spectrum of Supersonic Turbulence in Perseus , 2006, astro-ph/0611248.

[36]  N. Peretto,et al.  Herschel view of the Taurus B211/3 filament and striations: evidence of filamentary growth? , 2012, 1211.6360.

[37]  R. Klessen.  Star Formation in Molecular Clouds , 2011, 1109.0467.

[38]  James J. Bock,et al.  BLAST: THE MASS FUNCTION, LIFETIMES, AND PROPERTIES OF INTERMEDIATE MASS CORES FROM A 50 deg2 SUBMILLIMETER GALACTIC SURVEY IN VELA (ℓ ≈ 265°) , 2009, 0904.1207.

[39]  A. Lyne,et al.  Pulsar Rotation Measures and the Large-Scale Structure of the Galactic Magnetic Field , 2006, astro-ph/0601357.

[40]  Jessie L. Dotson,et al.  DISPERSION OF MAGNETIC FIELDS IN MOLECULAR CLOUDS. II. , 2008, 0909.5227.

[41]  James J. Bock,et al.  BLAST: RESOLVING THE COSMIC SUBMILLIMETER BACKGROUND , 2009, 0904.1205.

[42]  P. Padoan,et al.  A Super-Alfvénic Model of Dark Clouds , 1999, astro-ph/9901288.

[43]  Di Li,et al.  THE MAGNETIC FIELD IN TAURUS PROBED BY INFRARED POLARIZATION , 2011, 1108.0410.

[44]  A. Lazarian,et al.  Radiative torque alignment: essential physical processes , 2007, 0707.3645.

[45]  N. Ysard,et al.  Separation of anomalous and synchrotron emissions using WMAP polarization data , 2008, 0802.3345.

[46]  G. Novak,et al.  DISPERSION OF OBSERVED POSITION ANGLES OF SUBMILLIMETER POLARIZATION IN MOLECULAR CLOUDS , 2007, 0707.2818.

[47]  V. Ossenkopf,et al.  Turbulent velocity structure in molecular clouds , 2000, astro-ph/0012247.

[48]  R. Klessen,et al.  From the warm magnetized atomic medium to molecular clouds , 2008, 0805.1366.

[49]  California Institute of Technology,et al.  Dispersion of Magnetic Fields in Molecular Clouds , 2008 .

[50]  James M. Stone,et al.  Density, Velocity, and Magnetic Field Structure in Turbulent Molecular Cloud Models , 2000, astro-ph/0008454.

[51]  J. Fiege,et al.  Polarized Submillimeter Emission from Filamentary Molecular Clouds , 2000, astro-ph/0005363.

[52]  Antonio Pereyra,et al.  Polarimetry toward the Musca Dark Cloud. I. The Catalog , 2004 .

[53]  A. Z. Dolginov,et al.  Orientation of cosmic dust grains , 1976 .

[54]  C. D. Wilson,et al.  MAGNETIC FIELDS IN STAR-FORMING MOLECULAR CLOUDS. II. THE DEPOLARIZATION EFFECT IN THE OMC-3 FILAMENT OF ORION A , 2001 .

[55]  G. Kowal,et al.  DENSITY STUDIES OF MHD INTERSTELLAR TURBULENCE: STATISTICAL MOMENTS, CORRELATIONS AND BISPECTRUM , 2008, 0811.0822.

[56]  G. Kowal,et al.  Studies of Regular and Random Magnetic Fields in the ISM: Statistics of Polarization Vectors and the Chandrasekhar-Fermi Technique , 2008, 0801.0279.

[57]  David Nutter,et al.  The balloon-borne large-aperture submillimeter telescope for polarimetry-BLASTPol: performance and results from the 2010 Antarctic flight , 2012, Other Conferences.

[58]  C. Loore,et al.  The Formation of Stars , 1992 .

[59]  M. Lombardi,et al.  ON THE STAR FORMATION RATES IN MOLECULAR CLOUDS , 2010, 1009.2985.

[60]  J. Greenstein,et al.  The Polarization of Starlight by Aligned Dust Grains. , 1951 .

[61]  Peter G. Martin,et al.  Interstellar polarization from a medium with changing grain alignment , 1974 .

[62]  W. A. Hiltner,et al.  Polarization of Light From Distant Stars by Interstellar Medium. , 1949, Science.

[63]  H. Roussel,et al.  From filamentary clouds to prestellar cores to the stellar IMF: Initial highlights from the Herschel Gould Belt survey , 2010, 1005.2618.

[64]  A. Lazarian,et al.  GRAIN ALIGNMENT INDUCED BY RADIATIVE TORQUES: EFFECTS OF INTERNAL RELAXATION OF ENERGY AND COMPLEX RADIATION FIELD , 2008, 0812.4576.

[65]  S. Basu,et al.  Three-dimensional Simulation of Magnetized Cloud Fragmentation Induced by Nonlinear Flows and Ambipolar Diffusion , 2008, 0804.4303.

[66]  Gopal Narayanan,et al.  Large-Scale Structure of the Molecular Gas in Taurus Revealed by High Linear Dynamic Range Spectral Line Mapping , 2008, 0802.2206.

[67]  T. Mouschovias.  Nonhomologous contraction and equilibria of self-gravitating, magnetic interstellar clouds embedded in an intercloud medium: Star formation. I Formulation of the problem and method of solution , 1976 .

[68]  R. Klessen,et al.  Comparing the statistics of interstellar turbulence in simulations and observations - Solenoidal versus compressive turbulence forcing , 2009, 0905.1060.

[69]  Giles A Novak,et al.  Detection of submillimeter polarization in the Orion nebula , 1984 .

[70]  Magnetic fields in molecular clouds , 2012 .

[71]  B. Draine,et al.  Theory of Interstellar Shocks , 1993 .

[72]  John E. Vaillancourt.  Polarized Emission from Interstellar Dust , 2007 .

[73]  University of Chicago,et al.  Statistical Assessment of Shapes and Magnetic Field Orientations in Molecular Clouds through Polarization Observations , 2009, 0907.3730.

[74]  Alyssa Goodman,et al.  Theoretical Models of Polarized Dust Emission from Protostellar Cores , 2001 .

[75]  F. Adams,et al.  Star Formation in Molecular Clouds: Observation and Theory , 1987 .

[77]  Structure Function Scaling in the Taurus and Perseus Molecular Cloud Complexes , 2002, astro-ph/0207568.

[78]  Ramprasad Rao,et al.  Magnetic Fields in the Formation of Sun-Like Stars , 2006, Science.

[79]  P. Hennebelle,et al.  Turbulent molecular clouds , 2012, 1211.0637.

[80]  J. Dotson,et al.  Polarized Far-Infrared Emission from the Core and Envelope of the Sagittarius B2 Molecular Cloud , 1997 .