Unveiling the role of the magnetic field at the smallest scales of star formation

Transcription

1 Unveiling the role of the magnetic field at the smallest scales of star formation Photo credit: C. Hull Chat Hull Jansky Fellow Harvard-Smithsonian Center for Astrophysics National Radio Astronomy Observatory 28 March 2017 NRAO Postdoc Symposium Charlottesville, VA

2 Overview Introduction: to magnetized star formation on large (~1 pc) & small (~1000 AU) scales Default assumption: the strong-field case Large-scale observations suggest strong fields. Small-scale observations sometimes do but not always ALMA results definitively show a weak-field case ALMA results also show a case where the magnetic fields are shaped by the bipolar outflow! Chat Hull NRAO Postdoc Symposium 28 Mar

3 Scales of star formation > 1 pc 0.1 pc cloud core 1000 AU < 100 AU envelope disk Chat Hull NRAO Postdoc Symposium 28 Mar

4 Intro: Magnetized star formation on large (cloud, ~parsec) scales Chat Hull NRAO Postdoc Symposium 28 Mar

5 Magnetic fields on cloud scales Musca dark cloud Fields perpendicular to cloud s long axis: fields may be dynamically important 10 pc Polarization Magnetic field Pereyra & Magalhães 2004 Chat Hull NRAO Postdoc Symposium 28 Mar

6 Polarization (dust absorption) ALIGNED DUST GRAINS Polarization traces magnetic field orientation ORDERED MAGNETIC FIELD BACKGROUND STAR (unpolarized) Chat Hull NRAO Postdoc Symposium 28 Mar

7 Polarization (dust emission) ALIGNED DUST GRAINS Polarization must be rotated by 90º to show magnetic field orientation ORDERED MAGNETIC FIELD BACKGROUND STAR (unpolarized) Chat Hull NRAO Postdoc Symposium 28 Mar

8 Magnetic fields on cloud scales Musca dark cloud 10 pc Polarization Magnetic field Pereyra & Magalhães 2004 Chat Hull NRAO Postdoc Symposium 28 Mar

9 Magnetic fields on cloud scales Musca dark cloud 10 pc 353 GHz (850 microns) Pereyra & Magalhães 2004 E,B Planck XXXIII, 2014 Planck XXXIII, 2014 Chat Hull NRAO Postdoc Symposium 28 Mar

10 Magnetic field from dust emission (Planck) is consistent with dust absorption (optical) Magnetic fields on cloud scales Musca dark cloud 10 pc Pereyra & Magalhães 2004 agnetic field Polarization Magnetic field Planck XXXIII, 2014 Chat Hull NRAO Postdoc Symposium 28 Mar

11 Magnetic fields on large (Planck) scales 20 pc Scaled to nearby SFRs. 2. Locations and sizes of the regions selected Planck for Collaboration analysis. The2015, background paper XXXV map is the gas column density, N, derived fro Chat Hull NRAO Postdoc Symposium 28 Mar

12 Magnetic fields on large (Planck) scales 20 pc Scaled to nearby SFRs Planck Collaboration planckandthemagneticfield.info Chat Hull NRAO Postdoc Symposium 28 Mar

13 HRO analysis HRO = Histogram of Relative Orientation (see Soler+2013) The HRO characterizes the relationship between magnetic fields and filamentary structures in the dust and gas Number DENSE GAS Planck XXXV (Soler+2015) B filament Chat Hull NRAO Postdoc Symposium 28 Mar

14 HRO analysis A random HRO indicates that the magnetic field is not dictating the morphology of the star-forming material Number Planck XXXV (Soler+2015) B filament Chat Hull NRAO Postdoc Symposium 28 Mar

15 Musings on large (Planck) scales Planck conclusions: B-fields in dense gas tend to be to filament axis Formed by gravitational collapse along field lines? B-fields are important on large (~pc) scales But what about small (<1000 AU) scales? Chat Hull NRAO Postdoc Symposium 28 Mar

16 What is the role of the magnetic field in star formation? Fundamental? Incidental? Chat Hull NRAO Postdoc Symposium 28 Mar

17 Intro: Magnetized star formation on small (<1000 AU) scales Chat Hull NRAO Postdoc Symposium 28 Mar

18 The strong-field scenario (C) (D) The large-scale magnetic field in the ISM (~100 pc) seems to be preserved (E) (F) in the small-scale cores (0.1 pc) (G) (H) Hua-bai Li+2009 Chat Hull NRAO Postdoc Symposium 28 Mar

19 10 10 Consistent fields at even smaller scales sometimes Magnetic field orientation is frequently consistent from 10, AU scales Declination (J s 54.0 s Right Ascension (J2000) B field Declination (J2000) 53.5 but s 4 sometimes h 39 m 53.0 s it isn t 54.4 s 54.2 s 54.0 s 53.8 s Right Ascension (J2000) 53.6 s Declination (J2000) 25 (c) HH s 58.0 s 57.0 s 56.0 s Right Ascension (J2000) 6000 AU 55.0 s Declination (J2000) 35 B field h 43 m 54.0 s 45 (c) L1527 Hull+2014, TADPOL survey 56.0 s 55.0 s 54.0 s 53.0 s Right Ascension (J2000) 3000 AU 4 h 39 m 51.0 s me as Figure 4. (a) The velocity ranges of the CO(J = 2 1) line wing Figure emission 17. L1527. are 29.6 Same to 12.6 as Figure km s 1 4. (redshifted) (a) The velocity and 6.3 ranges to of the CO(J = 2 1) line wing emission are 12.9 to 9.7 km s 1 (redshifted) and 2 SL = 1.03 K km s 1.(b)σ I = 3.5mJybeam 1. (blueshifted). σ SL = 0.32 K km s 1.(b)σ I = 1.0mJybeam 1. e and associated FITS images and machine-readable tables are available in (A thecolor onlineversion journal.) of this figure and associated FITS images and machine-readable tables are available in the online journal.) 52.0 s B field See also Davidson+2014, incl. C. Hull Chat Hull NRAO Postdoc Symposium 28 Mar

20 The canonical picture: hourglass fields The typical initial condition for the magnetic field in models of star-forming cores is an hourglass with its symmetry axis aligned with the core s rotation axis (see also Fiedler & Mouschovias 1993) Allen, Li, & Shu 2003 Chat Hull NRAO Postdoc Symposium 28 Mar

21 The canonical picture Note the thin, blue magnetic field lines in an hourglass shape ~50 AU Credit: Bill Saxton, NRAO/AUI KALYPSO project, Harvard/CfA 21

22 Sightings of the fabled hourglass B-field IRAS 4A L1157 Girart AU 1000 AU Hull+2014, TADPOL survey See also Stephens+2013, incl. C. Hull 500 AU Chat Hull NRAO Postdoc Symposium 28 Mar

23 CARMA Combined Array for Research in Millimeter-wave Astronomy Consortium: Berkeley, Caltech, Illinois, Maryland, Chicago 6 10-m, 9 6-m, and m telescopes Observations at 1 cm, 3 mm, and 1 mm (polarization!) Photo credit: C. Hull Was located in Cedar Flat, CA (near Bishop) This is me installing a 1 mm polarization receiver between 2010 and

24 TADPOL survey Chat Hull NRAO Postdoc Symposium 28 Mar

25 TADPOL results 1000 AU L1157 Hull+2014, ApJS, 213, 153 See also: Stephens+ (incl. C. Hull) 2013, ApJL, 769, L15 Chat Hull NRAO Postdoc Symposium 28 Mar

26 Chat Hull NRAO Postdoc Symposium 28 Mar Credit: Bill Saxton, NRAO/AUI KALYPSO project, Harvard/CfA

27 TADPOL results Ser-emb 8, 8(N) 1000 AU Hull+2014, ApJS, 213, 153 Chat Hull NRAO Postdoc Symposium 28 Mar

28 Outflow vs. B-field: distribution 0 CDF º 0 45º Random 70 90º Hull+2013, ApJ, 768, 159 (plot updated Feb 14) Simulation: outflows & B-fields aligned within a 20º cone (tightly aligned) Simulation: outflows & B-fields are randomly oriented Simulation: outflows & B-fields aligned between 70 90º (preferentially misaligned) 0º θ outflow θ B-field (deg) 90º Chat Hull NRAO Postdoc Symposium 28 Mar

29 ALMA observations Chat Hull NRAO Postdoc Symposium 28 Mar

30 ALMA Photo credit: C. Hull Chat Hull NRAO Postdoc Symposium 28 Mar

31 Cycle 2, 3, & 4 ALMA obs. Ser-emb 6 (a.k.a. SMM1) Class 0 CORE POLARIZATION (PI: Hull) 0.36ʺ dust 850 um Ser-emb 8(N) 0.36ʺ and 1ʺ lines & 1 mm Cycles 3 & 4: 0.06ʺ dust 850 um Ser-emb 8 Probing ~1000 à25 AU disk scales Hull+2014, TADPOL survey Chat Hull NRAO Postdoc Symposium 28 Mar

32 JCMT Serpens Main 85,000 AU Hull, Mocz, Burkhart+2017, under revision (data from Matthews+2009) Chat Hull NRAO Postdoc Symposium 28 Mar

33 CARMA Ser-emb 8(N) Ser-emb 8 15,000 AU Hull, Mocz, Burkhart+2017, under revision (data from Hull+2014) Chat Hull NRAO Postdoc Symposium 28 Mar

34 ALMA Ser-emb AU Hull, Mocz, Burkhart+2017, under revision Chat Hull NRAO Postdoc Symposium 28 Mar 2017

35 Chat Hull NRAO Postdoc Symposium 28 Mar LIC image credit: Phil Mocz

36 JCMT CARMA ALMA 85,000 AU [= 0.41 pc] 15,000 AU [= 0.08 pc] 3500 AU Hull, Mocz, Burkhart+2017, under revision

37 JCMT CARMA ALMA 85,000 AU [= 0.41 pc] 15,000 AU [= 0.08 pc] 3500 AU The ALMA-scale magnetic field, which is attached to the forming stellar system, is not reminiscent of the large-scale field. No hourglass! This is in contrast to 50 years of theory, and to recent papers such as Li+2009, who suggested that the large-scale mean field direction could be preserved all the way down to the scale of forming stars. Hull, Mocz, Burkhart+2017, under revision

38 B=1 Keep an eye on the magnetic field strength here (in microgauss) AREPO simulations Chat Hull NRAO Postdoc Symposium 28 Mar

39 B=1 JCMT scales JCMT/CARMA scales ALMA scales 1 million AU [= 5 pc] AU [= 0.2 pc] 3000 AU Hull, Mocz, Burkhart+2017, under revision

40 B=10 1 million AU [= 5 pc] AU [= 0.2 pc] 3000 AU Hull, Mocz, Burkhart+2017, under revision

41 B=30 1 million AU [= 5 pc] AU [= 0.2 pc] 3000 AU Hull, Mocz, Burkhart+2017, under revision

42 B=100 1 million AU [= 5 pc] AU [= 0.2 pc] 3000 AU Hull, Mocz, Burkhart+2017, under revision

43 HRO analysis HRO = Histogram of Relative Orientation (see Soler+2013) The HRO characterizes the relationship between magnetic fields and filamentary structures in the dust and gas Number DENSE GAS Planck XXXV (Soler+2015) B filament Chat Hull NRAO Postdoc Symposium 28 Mar

44 HRO analysis A random HRO indicates that the magnetic field is not dictating the morphology of the star-forming material Number Planck XXXV (Soler+2015) B filament Chat Hull NRAO Postdoc Symposium 28 Mar

45 HRO analysis: ALMA & AREPO The ALMA data exhibit a random HRO. The strongly magnetized simulation, has a dynamically important magnetic field, but is inconsistent with our ALMA data Data Field strength really weak weak moderate strong Hull, Mocz, Burkhart+2017, under revision B filament B filament Chat Hull NRAO Postdoc Symposium 28 Mar

46 A statistical comparison shows that the ALMA observations best match the weakly magnetized simulations 1 million AU [= 5 pc] AU [= 0.2 pc] 3000 AU We have shown an alternate mode of star formation where the small-scale magnetic field morphology is dictated by turbulence and not by the large-scale magnetic field Hull, Mocz, Burkhart+2017, under revision 46

47 CARMA ALMA No. 2, 2006 CLOUD EVOLUTION WITH OBLIQUE FIELD 1237 Hull, Mocz, Burkhart+2017, under revision FUTURE WORK: are the deviations at small scales due to toroidal wrapping of fields by disk rotation? This will be answered by my Cycle 3 enlarged view of the center. ~30 AU polarization observations, which were recently taken! Fig. 10. Same as Fig. 5 (left), but for model C45. The lower left inset is an Fig. 11. Same as Fig. 1, but for C00 at the core formation epoch. 47

48 The plot thickens Serpens SMM1, the nearby neighbor of Ser-emb 8, has an outflow that is shaping the magnetic field! Chat Hull NRAO Postdoc Symposium 28 Mar

49 a 5,000 AU JCMT Multi-scale obs. of Serpens SMM1 80,000 AU [= 0.39 pc] d d ALMA b CARMA c a b 12,000 AU c SMA Hull, Girart+2017, in prep. 1,000 AU

50 Smoothing of polarized intensity maps a ALMA (native resolution) b ALMA (smoothed to CARMA res.) c Same linear scale as panel a CARMA (native resolution) Hull, Girart+2017, in prep.

51 Hull, Girart+2017, in prep.

52 Outflow shaping the magnetic field Hull, Girart+2017, in prep.

53 Summary (Ser-emb 8) ~100 AU resolution ALMA observations of magnetic fields in Ser-emb 8 Field orientation not preserved from large scales No hourglass! High-DR, ALMA-resolution AREPO simulations Initial conditions of the cloud dictate what we see at small scales We see an alternate mode of star formation where the field morphology is dictated by turbulence and not by a strong B-field Chat Hull NRAO Postdoc Symposium 28 Mar

54 Summary (Ser SMM1) The outflow from Serpens SMM1 appears to be shaping the magnetic field Why is this? More evolved? Hints of an hourglass but one created by the outflow? Chat Hull NRAO Postdoc Symposium 28 Mar

55 Fin Chat Hull NRAO Postdoc Symposium 28 Mar