S-PASS, a new view of the polarized sky

Gianni Bernardi

SKA SA

On behalf of the S-PASS team

CMB2013, Okinawa, June 10-14th 2013

CMBleaks from CMB2013…

Thank you for the great conference!

Motivation 1: Polarized synchrotron emission is a foreground for CMB observations;

Motivation 2: Galactic science (particularly the magnetic field)Synchrotron polarized emission magnetic field orientation (and strength)

Synchrotron polarized emission at multiple frequencies Faraday rotation measurement of the magnetic field strength, orientation and direction parallel to the line of sight

Θ=Θ0+RM λ2 RM=∫

L

0

ne B⃗ ⋅d l⃗

RM 220 rad m− 2( ne0.03cm− 3 )( B∥

3 μG )( L3kpc )

Motivation 2: Galactic science

37543 extragalactic RMs (reprocessing of NVSS data, Taylor et al. 2009) simultaneously show large-scale coherence & small-scale fluctuations

Predecessor: the Parkes Galactic Meridian Survey (PGMS) PI: E. Carretti

• 5° deg b-strip at l ~ 254°;

• 2.3 GHz, 160 MHz bandwidth (2 MHz channels with high spectral isolation to reject RFI);

• 9’ arcmin angular resolution;

• 0.3 mK/pixel sensitivity (3’ pixel);

• 0.3 on axis instrumental pol;

• < 1% off axis instrumental pol;

Carretti et al., 2010

Map-making

• Cross scans and Emerson & Grave map-making technique of data at constant azimuth;

• A quadratic fit to each elevation bin removes the ground pick up effectively

• Disc region b > -20°, small scale structure;

• Halo region b < -40°, lack of small scale structure, smooth emission;

Foregrounds for CMB B-mode

Evolution: the S-band Parkes All-Sky Survey (S-PASS) E. Carretti (PI), G. Bernardi. B.M. Gaensler. M. Haverkorn, M.Kesteven, S. Poppi. L. Staveley-Smith

• To survey the polarized emission of the entire southern sky at 2.3 GHz

– Dec < 0º (unshaded area);– Parkes: 2.3 GHz ;– 224 MHz BW (100+ ch);– FWHM = 9’;– sbeam < 1.0 mK;

– 2000 h– 175 nights in 2.5 yrs

– Started 07, completed in 2010– Goals: synchrotron emission, Galactic magnetic field, CMB foregrounds

depolarization

• All sky maps at 1.4 GHz, FWHM 36’;• Single channel surveys: no RM measures;

• Galactic Disc strongly depolarized |b| < 30° call for higher frequency (depolarization is frequency dependent)

The 1.4 GHz scenario

• small area basket weaving: not an option for S-PASS– ground emission contamination (EL dependant)– high speed requires significant overhead for short scans (10o-20o)– short scans: mean emission on area scale is lost

• New exotic/non-standard scanning strategies has been developed for S-PASS– AZ scans – Long AZ scans at South Pole EL to cover all Dec in one haul (~115o)– uses the Sky rotation to observe all RA 24 hrs.– each day/night a zig-zag track is observed in the sky– one zig-zag per night: accurate start timing is required

Mapping: fast (120°/8 min), extended AZ scans (minimize ground pick up and 1/f noise)

Results: total & polarized intensity

Results: Stokes Q

Results: Stokes U

WMAP & S-PASS

Page et al. (2003) model

WMAP & S-PASS

23 GHz

2.3 GHz

Northern Lobe

Southern Lobe

Giant Magnetized Outflows from the Centre of the Milky Way

Carretti et al., 2013

Conclusions

• Synchrotron polarization is a unique probe of the ISM, particularly of the Galactic magnetic field and the density of the thermal gas. It is also a relevant contaminant for CMB polarization observations on large scales, particularly looking for the CMB B-mode;

• We have completed a 2.3 GHz polarization survey of the southern sky with 9’ resolution. The survey has SNR > 5 (9’ arcmin beam) over 96% of the observed sky;

• We “stumbled upon” two giant polarized plumes connected with the Galactic Centre they morphologically match the γ-ray bubbles – and the extended Planck haze. The plumes/haze/bubbles can be explained as the result of massive star formation at the Galactic Centre – but it might not be the end of the story;

• Several ongoing activities: foreground estimates in low emission regions, comparison with the 1.4 GHz and 23 GHz data, analysis of bright regions (Gum nebula), point source RM;

• We aim at a near future data release (~2 months?); people could use it to estimate foreground contamination in the CMB data a/o include them in their foreground subtraction process (the high latitude emission does not seem to be affected by Faraday rotation – wee next C-BASS talk for more on this);

THANK YOU