The Global Magneto-Ionic Medium Survey

Transcription

1 The Global Magneto-Ionic Medium Survey

2 The Global Magneto-Ionic Medium Survey studying the polarized emission from the Galaxy

3 The Global Magneto-Ionic Medium Survey GMIMS studying the polarized emission from the Galaxy

4 2. Wielebinski, The Past Shakeshaft, Low-Resolution & Pauliny-Toth, 1962 Mapping 408 MHz Angular resolution 8 o The discovery of polarization was the final proof that the Galactic radio emission was generated by the synchrotron mechanism Equipartition between magnetic field and relativistic electrons Magnetic field is about 5 μg

5 1.411 GHz Dwingeloo polarization survey Brouw & Spoelstra, 1976, AAS, 26, 129 Highest frequency coverage of the whole Northern sky. Beam 0.6 deg, sampling 2 to 5 deg. Sky coverage 2%

6 1.4 GHz total intensity beam 36 arcmin 1.4 GHz polarized intensity DRAO 26-m 2006

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8 1.4 GHz total intensity beam 36 arcmin 1.4 GHz polarized intensity

9 The polarized sky does not resemble the total-intensity sky

10 Faraday Rotation Faraday rotation dominates the appearance of the polarized sky at decimetre wavelengths

11 Faraday Rotation The astrophysics is in this product Faraday rotation dominates the appearance of the polarized sky at decimetre wavelengths

12 Global Magneto-Ionic Medium Survey Synchrotron radiation is generated everywhere in the Milky Way Faraday rotation occurs along most paths In principle, the extended polarized emission can tell us about Galactic magnetic fields We have set out to map the magnetic field by mapping polarized emission from the entire sky, North and South using big single antennas from 300 MHz to 1800 MHz beamwidths 0.5 to 1 degree with many frequency channels exploiting RM synthesis

13 The GMIMS Consortium Tom Landecker (PI) Andrew Gray Maik Wolleben Kevin Douglas Jo-Anne Brown Russ Taylor Ettore Carretti Naomi McClure-Griffiths Alex Hill David McConnell Bryan Gaensler Xiaohui Sun Cormac Purcell John Dickey Roland Crocker Wolfgang Reich Dominic Schnitzeler Ann Mao Paddy Leahy Andrew Fletcher Marijke Haverkorn Han Jinlin DRAO Canada U Calgary Canada U Capetown CSIRO Australia U Sydney Australia U Tasmania Australia Australian National University Max-Planck-Institut, Germany U Manchester UK U Newcastle UK Radboud U Netherlands NOAC China

14 The Global Magneto-Ionic Medium Survey Frequency band MHz MHz MHz SOUTH Parkes Parkes 64-m 64-m 100% 100% NORTH DRAO 26-m 100% status of observations

15 The Global Magneto-Ionic Medium Survey Frequency band MHz MHz MHz SOUTH Parkes Parkes 64-m 64-m NORTH 90% done for 290 to 480 MHz 0% DRAO 26-m 95% status of data processing

16 The Global Magneto-Ionic Medium Survey Frequency band MHz MHz MHz SOUTH Parkes Parkes 64-m 64-m NORTH 90% done for 290 to 480 MHz 0% DRAO 26-m 95% status of data processing

17 The DRAO Survey to 1750 MHz

18 New techniques in wideband antennas and processing FPGA processor, BW 500 MHz

19 DRAO GMIMS Survey 90 DEC % DEC % -30 0h R.A. 24h

20 1.4 GHz Total Intensity Reich & Reich Galactic Centre mostly synchrotron emission

21 Rotation Measure Synthesis of the Northern Sky GHz (resolution 1 deg)

22 Previous Faraday Rotation Maps current FR maps of the sky have low angular resolution. Pulsars (Han et al, 1999) A0 dynamo EG sources (Taylor et al, 2009)

23 A New (High-Resolution) Faraday Rotation Map - Using a peak finder algorithm we can use the RM-Synthesis cube to generate a FR map. - Small-scale structure in the FR sky: 4 filaments, must be structures in the magnetic field Wolleben et al. (2010)

24 RM Bubble 60 rad/m 2 0 rad/m 2 - Polarized, filamentary structures at +60 rad m -2, 0 rad m -2, and -50 rad m rad/m 2 - parts of a shell; roughly resembling the shape of a bubble - highly Faraday rotated

25 RM Bubble - Polarized filaments associated - with an HI bubble - large local - partly positive correlation between PI and HI; other parts anti-correlated; also depends on velocity (LAB HI Survey, Kalberla 2005) - no Hα emission: B II 30 μg Wolleben et al. (2010)

26 RM Bubble? - Suggests that antisymmetry in the northern Galactic halo actually caused by a local object with a strong magnetic field. - But also makes an important point: We have to use all probes available (Pulsars, EGS, and the diffuse emission) to study the magnetic field.

27 data reduction by Maik Wolleben and Kevin Douglas MHz DRAO 26-m

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29 Absolute calibration aperture efficiency The survey is calibrated using strong point sources. The aperture efficiency converts Janskys to Kelvins. (Xuan Du)

30 Target dates: Completion of processing for DRAO data: March 2015 Completion of processing for Parkes MHz: December 2014 Start of processing for Parkes data: January 2015