Magnetic Field Structure in Molecular Clouds by Polarization Measurements

1. Magnetic Field Structure in Molecular Clouds by Polarization Measurements Collaborators: C. Eswaraiah (ARIES), S. P. Lai (NTHU), C. D. Lee (NCU), C. C. Lin (NCU), A. K. Pandey (ARIES), Shuji Sato (Nagoya U), Y. H. Shi (NCU), Bohe Su (NCU), M. Tamura (NAOJ), J. W. Wang (NTHU) Wen-Ping Chen National Central University

2. Magnetic Field and Star Formation • What is the field strength and structure on different length scales (hence densities) from the molecular cloud, core, to protostar? • B suppresses cloud fragmentation/collapse; ambipolar diffusion reduces the strength, hence the influence of, the field. • Bcollates filaments? Guides core collapse and mass outflows?

3. Observations in OIR Stahler & Pallo 2004 Scattering by dust Dichroic extinction by aligned dust Observations in FIR to mm Courtesy: Tamura Polarized thermal emission by dust aligned by B

4. Polarization of Background Stars --- Dichroic extinction by thermalized, magnetically aligned dust • Background stars should be otherwise unpolarized. • IR less extinction than the optical, so probes deeper into the cloud (more background stars) but less effective • To derive the Binformation, need to sort out which mechanism is at work. • To infer if cloud geometry influenced by B, need to isolate other effects, e.g., by shocks. The Rho Oph cloud (Vrba et al. 1976) The Rho Oph cloud (Stahler & Palla 2004; data from Loren 1989 and Goodman et al. 1990)

5. Our program To probe the B structure • on protostellar scales and on the inner part of a cloud core by SMA, and soon by ALMA; disk/outflow configuration • on the outer part of a cloud core by NIR polarization (e.g., SIRPOL) • on the periphery of a cloud core by optical polarization (e.g., TRIPOL)

6. SIRPOL--- SIRIUS(Simultaneous IR imager for Unbiased Survey) with polarimeter • IRSF 1.4 m telescope at SAAO • Simultaneous JHKs imaging polarimeter • FOV 7.7’, (1 K x 1 K x 3 bands, 0.45”/pix) • Imaging sensitivity, J=19.2, H=18.6, Ks=17.3 mag (S/N=5; 60 min) • Pol sensitivity, J < 16.5, H < 15.7, Ks < 14.5 (dP < 0.3-1%) Tamura et al. 2006 on the Orion Nebula

7. The Carina nebula(NGC 3372) RA = 10:45:08.5, Dec = ‒59:52:04 is a large bright nebula powered by UV radiation from 65 O-type stars and 3 WNH stars (Smith et al. 2008), including the most massive and luminous star in the Milky Way, Eta Carinae. At a distance of 2.3 kpc, the Carina nebula is a good laboratory to study massive star formation. RCW 57A (NGC 3576) RA= 11:11:54.8Dec = ‒61:18:26 is among the brightest Galactic HII regions, hosting many IR excess stars and some high-mass Class 0/I objects (Barbosa et al. 2003). At a distance of 2.4 kpc (Persi et al. 1994), RCW57 is also a good target to study star formation in a turbulent environment.

8. Carina Nebula RCW 57A DSS 5 deg

9. Only reliable measurements (ΔP < 0.5% or P/ΔP > 3 and ΔH < 0.05 mag) are included.

10. H band 12CO(J = 1−0) emission (Yonekura et al. 2004) Carina nebula RCW 57A

11. Carina nebula [Background = foreground = Galactic] in polarization because the SIRPOL field is devoid of dense cloud.  No B information The whole region was mosaicked in the spring of 2012.

12. Rcw 57A Hour-glass shaped B threading the elongated cloud [S II]

13. Grey lines: H-band pol Central curve: 13CO Dashed lines: HII region (3.4 cm) Pluses: H2O maser sources Filled squares: IRAS sources Triangles: Class I Open squares: Class II cavities, bubble H-band stellar polarization overlaid on the WISE 4.6 micron image Eswaraiah+2012 prep

14. Foreground stars toward RCW57A and Carina Nebula with V-band polarization (Heiles 2000) and Hipparcos parallaxes (van Leeuwen 2007). • By assuming Pmax= 1.0%, max =0.55 micron, K=1.15 and by using the Serkowski's relation P/Pmax= exp[ -K * ln2 (max/ ) ] So the foreground polarization in NIR is negligible • PJ < 0.65 % (J=1.25 micron)PH < 0.46 % (H=1.63 micron) PKs < 0.30 % (K=2.14 micron) • P internal in RCW 57A • no external perturber to shape the cloud

15. TRIPOL--- Tri-color Imaging Polarimeter • Designed and fabricated by Prof. Shuji Sato of Nagoya U. • Prototype completed in 2011, tested on Lulin one-meter telescope (LOT) , now on the 75 cm telescope at SAAO. • Second unit completed in 2012, now as facility instrument at Lulin. • Meant to be simple, robust, versatile, and economic, particularly suitable for small telescopes. • Simultaneous imaging at gri bands

16. 3 Color Imaging & a Polarizer plain imager CCD F10 -------------------------------------------------------------------------------------------------------------- g 3 channel 3-CCD i ½-plate r polarization wire-grid or birefringence

18. SBIG ~3000 US$

19. TRIPOL first light images: M16 in g’ (left), r’, and i’. TRIPOL images of M1 (top) polarized intensity and (bottom) total intensity in g’, r’, and i’ (left to right)

20. T Tauri stars HL Tau XZ Tau i’ r’ g’ TRIPOL images taken with the LOT in August 2011

21. CB3 --- a dark globule CB 3 g band

22. Ward-Thompson et al. (2009)

23. Conclusions • Polarization is a powerful tool to infer the magnetic field configuration in molecular clouds. • A combination of extinction (OIR) and thermal emission (FIR to mm) measurements will yield the field structure from small- to large-length scales. • In RCW 57A, there is possible evidence of B controlled cloud contraction. • Full operation of TRIPOL is scheduled in December 2012 to study cores with YSOs, starless cores, etc.