Magnetic fields of our Galaxy on large and small scales

Magnetic fields of our Galaxy on large and small scales JinLin Han National Astronomical Observatories Chinese Academy of Sciences hjl@bao.ac.cn

A small work dedicated to IAU 242 Published on mid-march 2007 on time, A&A 464, 609

Magnetic fields of our Galaxy on large and small scales Background Galactic structure ISM & Masers Galactic B-fields: B large-scales Detection and modeling (co: R.N. Manchester & A.G. Galactic B-fields: B small-scales scales Observational results (partial Review) arm-separation! (co: R.N. Manchester & A.G. Lyne) Connection of Galactic B-fields B of large and small scales Conclusions

Magnetic fields of our Galaxy on large and small scales Background Galactic structure ISM & Masers Galactic B-fields: B large-scales Detection and modeling (co: R.N. Manchester & A.G. Lyne) Galactic B-fields: B small-scales scales Observational results (Review) Connection of Galactic B-fields B of large and small scales Conclusions

Why to study magnetic field? Origin: primordial or dynamo? Key information to cosmic rays! Key roles in star formation/clouds Hydrostatic balance & stability in ISM - However, Knowledge on the Galactic magnetic field is far from enough!

Our Milky Way Galaxy: Magnetic field? Optical sky Radio sky Our Galaxy: we live near the edge! We do not know the face-on structure what is the distribution of GMC/Star-formation regions! We want to work out Galactic magnetic fields: Where does it originate? How are they connected at large and small scales?

MilkyWay ISM: HI Clouds H2 or H+ /Dust Giant Clouds: Star- forming / HII regions /masers Structure Spiral arms? Permeated by the magnetic field lines! The Orion Nebula in the near-infrared (left panel: JHK "true-colour" image) and in the 1400 MHz radio continuum (right panel). The field shown is approximately 6' on a side.

Observational tracers of magnetic fields Polarization of starlight: perpendicular field in 2 or 3 kpc orientation // B ------------- 9000 stars Zeeman splitting: parallel field, in situ (masers, clouds) ν B // ------ 137 maser regions & 17 coulds Polarization at infrared, mm, submm: perpendicular field orientation // B ------------- clouds or regions Synchrotron radiation: vertical field structures (added) total intensity S B 2/7, p% B 2 u / B 2 t Faraday rotation: parallel field, integrated (the halo & disk) RM n e B // ds ------ 550 pulsars + >1200 EGSes

Starlight polarization: local field // arm 9000 stars have polarization measured mostly nearby (1~2kpc) polarization percentage increases with distance Zweibel & Heiles 1997, Nature 385,131 Berdyugin & Teerikorpi 2001, A&A 368,635

Magnetic fields of our Galaxy on large and small scales Background Galactic structure ISM & Masers Galactic B-fields: B large-scales Detection and modeling (co: R.N. Manchester & A.G. Lyne) Galactic B-fields: B small-scales scales Observational results (Review) Connection of Galactic B-fields B of large and small scales Conclusions IAU Symposium 242: Astrophysical Masers and their environments Mar.12-16 2007, Alice Springs, Australia

Galactic B-Field:10 years ago Halo B-field: no idea! 30kpc GC: Poloidal field Sun Galactic center Disk field: A few kpc! 3 models: which?

Large-scale Galactic B-fields: B Significant progress! New knowledge Fields near the GC Fields in the Galactic halo Fields in the Galactic disk IAU Symposium 242: Astrophysical Masers and their environments Mar.12-16 2007, Alice Springs, Australia

Poloidal & Toroidal fields near GC (from Novak et al. 2003) Predicted B-direction GC 150pc Toroidal fields (Novak et al. 2003, 2000) permeated in the central molecular zone (400pc*50pc) sub-mm obs of p% toroidal field directions determined by averaged RMs of plumes or SNR! Poloidal field filaments Unique to GC --- dipolar geometry! (Morris 1994; Lang et al.1999) IAU Symposium 242: Astrophysical Masers and their environments Mar.12-16 2007, Alice Springs, Australia

Magnetic fields in our Galaxy: near GC (from B.D.C. Chandran 2000) IAU Symposium 242: Astrophysical Masers and their environments Mar.12-16 2007, Alice Springs, Australia

To study halo field: unique to our Galaxy Extragalactic Radio Sources <B> away from us RM<0 RM distribution RM>0 <B> to us The largest edge-on Galaxy in the sky Pulsars and extragalactic radio sources as probes

Anti-symmetric RM sky (inner Galaxy): A0 dynamo (Han et al. 1997 A&A322, 98) Evidence for global scale High anti-symmetry to the Galactic coordinates Only in inner Galaxy nearby pulsars show it at higher latitudes Implications Consistent with field configuration of A0 dynamo The first dynamo mode identified on galactic scales

RMs of EGRs for the halo B-field B Only about 1200 RMs available in literature up to now... We have used Effelsberg -100m telescope to make a RM survey of 1700 sources, enlarge the cover density by a factor of three in most sky area

Southern RM sky? We are applying Parkes-64m telescope to improve the southern RM sky, enlarging the cover density by a factor of 20!

Magnetic fields of our Galaxy on large and small scales Galactic B-fields: B large-scales Detection and modeling (co: R.N. Manchester & A.G. Lyne) New knowledge Fields near the GC Fields in the Galactic halo Fields in the Galactic disk IAU Symposium 242: Astrophysical Masers and their environments Mar.12-16 2007, Alice Springs, Australia

Pulsars: Unique probes for Large-scale Galactic B-field 太阳银河中心 RM ne B // ds DM ne ds <B> = RM / DM

Why? Pulsars as probes for Galactic B-field Polarized. Widely spread in our Galaxy. Faraday rotation: e3 RM = 2π m e2 c 4 PSR Sun λ (l ) 2 n e ( l ) B ( l )[ ] dl = 0. 820 B λ obs Distances estimated from pulse dispersion: DM =»» <=== the delay tells DM t = 8.3 103 DM ν ν 3 MHz sec»» the rotation of position angles tells RM value ===>» Average field strength is B 1.232 RM µg DM RM = Dist Dist 0 0 n e dl ne dl PA λ 1 PA λ 2 λ12 λ 22

Pulsar RM distribution in Galactic plane Red: new measurements by Parkes 64m telescope (Han et al. 2006)

Pulsar Rotation Measure Authors Hamilton & Lyne (1987) Rand & Lyne (2004): Qiao et al. (1995) Van Ommen et al. (1997) Han et al. (1999) Crawford (2001): No. of RMs 163 27 48 24 63 7 No. New RMs 119 27 33 2 54 7 Mitra et al. (2003): Weisberg et al. (2003) Han et al. (2006): Total No. of pulsar RM published: ~ 554 11 36 223 11 17 196

Pulsar RM distribution in Galactic plane red: new measurements by Parkes 64m telescope RM B =1.232 µ G DM Han et al. 2002, ApJ 570, L17

Measured magnetic field in the Galactic disk RM B =1.232 µ G DM (Han et al. 2006, ApJ 642, 868)

Measured magnetic field in the Galactic disk always counterclockwise in arm region! clockwise in interarm region? Different from previous models! Tighter BSS? More data still needed! Han et al. 2006, ApJ 642, 868

Radial dependence of regular field strength (Han et al. 2006) B B R regular 0 B ( R R (R) =B0 exp[ RB = 2.1± 0.3µ G = 8.5 ± 4.7kpc ) ]

Measured magnetic field in the Galactic disk by pulsar rotation measures (Han et al. 2006)

Magnetic fields of our Galaxy on large and small scales Background Galactic structure ISM & Masers Galactic B-fields: B large-scales Detection and modeling (co: R.N. Manchester & A.G. Lyne) Galactic B-fields: B small-scales scales Observational results (Review) Connection of Galactic B-fields B of large and small scales Conclusions

Small-scale Galactic B-fields: B Great progress! Radio Polarization surveys of Galactic plane show B-field B structure Polarization obs of clouds Zeeman splitting mapping Spacial magnetic energy spectrum

Radio Polarization surveys of Galactic plane show B-field B structure Effelsberg Polarization Survey 20cm Parkes 2.7GHz polarization survey Canadian Galactic plane survey Southern Galactic plane survey VLA Galactic plane survey Galactic Arecibo-LFA survey Urumqi polarization survey of our Galaxy at 6cm

I (top( top) ) and PI (bottom( bottom) ) of a 24 x 9 9 large section centered at = 162,0,0 21cm Effelsberg Galactic Medium Latitude Survey From Wolfgang Reich s talk

Faraday Screen G191.2+2.4 From Wolfgang Reich s talk

Urumqi polarization Survey of our Galaxy First region: published 2007 March: Sun et al. A&A 463, 993 Known Objects HII region Sh 183 SNR G126.2+1.6 SNR G127.1+0.5 Reflective Nubula Sh 185 New Objects New HII region G124.0+1.4 New HII region G124.9+0.1 Newly discovered shell

Faraday Screen:G124.9+0.1 PI map dist:2.8 kpc size:22 pc ne:1.6 cm -3 Model-fitting: ψ=-50 o f=0.85 c=0.6 B =3.9 µg Emisivity: 6.3mK kpc -1

Small-scale Galactic B-fields: B Great progress! Radio Polarization surveys of Galactic plane show B-field B structure (Masers environment) Polarization observations of clouds Maser spots: VLBI? Single dish survey? Zeeman splitting Fish s s & Vlemmings Mapping polarization of clouds Vlemmings s review Crutcher s & Vlemmings s review (Masers environment) Statistics: Spatial magnetic energy spectrum

Spatial fluctuation spectrum for electron density Big Powerlaw in the Sky 10 pc (Armstrong, Rickett & Spangler 1995) Kolmogorov over 12 orders in scale? 1000 km B-field & electrons coupling? If so, B-energy spectrum?

Pulsar RM distribution onto Galactic plane red: new measurements by Parkes 64m telescope = PSR Sun RM n ( l) dl e( l) B

Spatial magnetic energy spectrum of our Galaxy (Han et al. 2004, ApJ 610, 820) By pulsar RM/DM Email from A. Minter Minter & Spangler 1996

Spiral arm RM structure function: * more turbulent than interarm region * turbulent at smaller scale (~17pc) (Haverkorn et al. 2006, ApJ 637, L33)

Magnetic fields of our Galaxy on large and small scales Background Galactic structure ISM & Masers Galactic B-fields: B large-scales Detection and modeling (co: R.N. Manchester & A.G. Lyne) Galactic B-fields: B small-scales scales Observational results (Review) Connection of Galactic B-fields B of large and small scales Conclusions

Connection of Galactic B-fields B of large and small scales Beck et al. 1991, IAUS 146, 209

Connection of Galactic B-fields B of large and small scales Galactic plane Li et al. 2006: ApJ ApJ 648, 340 (Results of SPARO 2003) Mapped large-scale magnetic fields in four GMCs Statistically significant correlation with the orientation of the Galactic plane. Field direction tends to be preserved during the process of GMC formation.

What happen to the B-fields B inside the clouds? Preserved from ISM B-field? Turbulence destroy the field structure? Fish et al. 2003 Reid et al. 1987

Previous results on the distribution of Zeeman splitting data Davies (1974): same sense of the Galaxy rotation!

Previous results on the distribution of Zeeman splitting data Davies (1974): same sense of the Galaxy rotation! Reid & Silverstein (1990) : 14/17 OH confirm!

Previous results on the distribution of Zeeman splitting data Davies (1974): same sense of the Galaxy rotation! Reid & Silverstein (1990) : 14/17 OH confirm! Caswell & Vaile (1995): 11/17 Baudry et al. (1997): 28/46 Fish et al.(2003) 41/74 OH

Measured magnetic field in the Galactic disk by pulsar rotation measures (Han et al. 2006)

Collecting data

The Galactic distribution of Zeeman data * Clear structure for the field directions * Field reversals in radial?

Statistics and model-comparison 1. count in rings 2. count in spirals

Magnetic fields of our Galaxy on large and small scales Background Galactic structure ISM & Masers Galactic B-fields: B large-scales Detection and modeling (co: R.N. Manchester & A.G. Lyne) Galactic B-fields: B small-scales scales Observational results (Review) Connection of Galactic B-fields B of large and small scales Conclusions

Conclusions Galactic B-fields: B large-scales GC: poloidal + toroidal fields Halo field: RM sky Disk field: Best measured by RMs of pulsars Galactic B-fields: B small-scales scales Polarization survey of the Galactic plane Polarization observations of clouds Zeeman splitting measurements or VLBI for maser spots Statistics: spatial spectrum or where is more turbulent Connection of Galactic B-fields B of large and small scales? Yes! Clouds fields, on average, may delineate the large- scale ISM B-field! B Used as complimentary tracers for large-scale fields

Thanks for your attention! Wisdom from this Chinese: Investigators using various tracers or approaches probe different parts of magnetic fields, and find different and even contradictory results, which are right in their own sense, but could be all left (not wrong) and complementary for reality.