Magnetic Fields over all Scales

Transcription

1 Magnetic Fields over all Scales Patrick Koch (ASIAA) 1 pc with: Hsuan-Gu Chou, Paul Ho, Ya-Wen Tang, Hsi-Wei Yen 30 mpc (CSO / 350µm, ~20 ) (JCMT / ~10 ) (SMA@ 345 GHz: ~ 3 to 0.7 ) JCMT Workshop, Taipei; January 23, 2015

2 goal: study magnetic field properties - working with the SMA, CSO (EACOA time), JCMT archive, ALMA - targets: high-mass star-forming systems to protostellar sources Tang+ 2009a, ApJ, 695, g5.89 Tang+ 2009b, ApJ, 700, W51 e2/e8 Koch+ 2010, ApJ, 721, magnetic fields and turbulence Tang+ 2010, ApJ, 717, Orion Koch+ 2012a, ApJ, 747, magnetic field strength technique Koch+ 2012b, ApJ, 747, magnetic field and star formation eff. Tang , ApJ, 763, W51 North Koch+ 2013, ApJ, 775, magnetic field interpretation Koch+ 2014, ApJ, 797, SMA + CSO sample analysis Yen , ApJ, in press -- dynamics and field in class O/I protostars

3 key questions: (1) morphology and role of the magnetic field, as a function of scale (2) quantitative assessment beyond imaging: field strength, level of turbulence, gravity, centrifugal force (3) microphysics: coupling of field to matter; e.g., combining magnetic field and velocity information, polarization properties as a function of frequency

4 Planck: Interstellar Medium Taurus molecular cloud complex; dust continuum at 350 GHz 15 resolution (Planck XXXII, arxiv: )

5 Planck: Interstellar Medium ξ=1: field aligned with ridges ξ=-1: field orthogonal to ridges magnetic field vs structure: - field tends to be aligned with ridges in diffuse ISM - alignment progressively changes as column density increases - interpretation: magnetic field is guiding material, possibly significant level of turbulence etc filamentary molecular cloud (Planck XXXII, arxiv: )

6 SMA: High-Resolution Cores in Star-Forming Regions Orion BN/KL Tang+10 W51 e2 Tang+09 NGC1333 IRAS 4A Girart+06 - among the currently highest-resolution polarization observations, ~ clearly resolved shaped and pinched field structures: often field closely aligned with gradients IRAS16293 Rao+09

7 more on smaller scales: SMA Polarization Legacy Program about 20 additional sources (new or deeper integration), high-mass sites with density > 10 5 cm -3 on scales pc (Zhang + SMA pol legacy, 2014, ApJ)

8 B major axis dominating in Planck data B major axis

9 SMA Polarization Legacy Program + CSO Archival data 50 sources magnetic field vs structure: - prevailing field orientation: roughly parallel to source minor axis - opposite to Planck result: field tends to be aligned with ridges in diffuse ISM - magnetic field very likely plays different roles as a function of scales qualitative analysis: * gravity dominating over field, typically supercritical allowing for faster collapse * field tension still significant, typically subcritical, slower or no collapse (Koch + SMA pol legacy, 2014, ApJ)

10 in between Planck and SMA (+ALMA) Scales 15 intermediate scales ~ 1? - filamentary structures - accretion zones goal: - fill in intermediate scales with the JCMT - look for magnetic field morphologies (+ dynamical velocity information) on intermediate scales

11 Earlier Example and Analysis: BIMA and SMA (BIMA: Lai et al., 2001) (SMA: Tang et al., 2009b) - distance 7 kpc, 5 Ultra-compact HII regions - collapsing phase, locally in e2, e mm (θ ~ 2.3 ) - uniform 0.87mm (θ ~ 0.7 ) - collapse - small scale structures resolved: split-monopole-like field structure - likely decoupled from larger scale field in envelope

12 W51 e2/e8: Filamentary Scale with BIMA Σ B <1: gravity dominating over field tension Σ B Σ B >1: field holding back gravitational collapse ϴ~2-3, Lai+2001) (Koch+2012b) magnetic field analysis: force ratio ΣB (Koch+ 12a,b) - new technique based on angle δ, utilizing field and dust continuum morphology - leads to dimensionless magnetic field-to-gravity force ratio

13 W51 e2/e8 : Filamentary Scale and beyond with SCUPOL (SCUPOL, Matthews+2009) -field structures in between and towards filaments and cores / envelopes - some information on how material is accumulated towards filaments and cores - outer zones: magnetic field has kept field tension, i.e., gravity not yet effective

14 Test Study with CSO / SHARP: G34 filament - CSO / Sharp observation, ϴ ~ 350 µm - clear detection in outer low-density region (Foster+2014) (Tang+ in prep.)

15 Possible Sample: SMA / CARMA Legacy Targets (CARMA, Hull+2014) (SMA, Zhang+2014)

16 What we would like to do with the JCMT: - samples: * SMA polarization legacy (also CARMA), Herschel, Planck-selected regions (high-/low-mass star-forming systems) * protostellar sources (based on SMA, CARMA) -needs: (1) SCUBA-2 (850µm and 450µm) + polarization with large fov, high-sensitivity in low-density regions (2) additional line information (field-gas coupling) - tools in place: quantitative assessment field strength, force ratio, turbulence