Polarization Surveys with the DRAO 26-m Telescope at 1.4 GHz Maik Wolleben, T. Landecker, O. Davison Dominion Radio Astrophysical Observatory W. Reich, R. Wielebinski Max-Planck-Institut für Radioastronomie

Outline 1)- The DRAO 26-m Polarization Survey (finished) - Brief Representation of Data 2)- The DRAO/MPI Rotation Measure Survey (ongoing )

Specifications TELESCOPE PARAMETER diameter: 25.6m polar mounting resolution: 37 arcmin aperture efficiency: 55 % hard limits: -34 to 90 deg system temperature: 125 K SURVEY PARAMETER frequency:1410 MHz bandwidth:12 MHz observing mode:drift scanning pixel-size:15 arcmin integration time:60 s / pixel First observing period: Nov 2002 – May 2003, coverage 17% Second observing period: Jun 2004 – Mar 2005, coverage 42%

Coverage - about 350 Meridian drift scans - about 350 Meridian drift scans - carried out by night (to avoid solar interference and ionospheric FR) - carried out by night (to avoid solar interference and ionospheric FR) - fully sampled along right ascension - fully sampled along right ascension - incomplete sampling along declination - incomplete sampling along declination

Calibration After correction: ● Effelsberg-MB scale ● Agrees with southern sky survey (Parkes-MB) ● Pole temperature 80mK Stokes U'Stokes Q' this response pattern (above) is not calibrated (max %pol roughly 6%) 1. ¼ of the observed signal is coming through the side lobes 2. instrumental polarization: side lobes are polarized → ground radiation correction

Calibration Observing & Calibration Strategy about 1000 pointings congruent with the Leiden/Dwingeloo 1 polarization survey: → provides zero-levels in Stokes U and Q (absolute levels) → used for the gain calibration of the receiving system (Müller matrix) ground radiation profiles: → required to extrapolate absolute zero-levels below 0° declination comparison with Effelsberg Medium Latitude Survey: → refines the (relative) temperature scale - includes correction for main-beam instrumental polarization - residual side lobe polarization visible along the Galactic plane (l ≈0° - 60°) - systematic errors due to scanning effects (system temperature variations) 1 A survey of linear polarization at 1415 MHz: Spoelstra, T. A. Th., A&AS, 1972

Errors correlation coefficients r U =0.89, r Q =0.86: → rms-noise: 12 mK (U), 33 mK (Q) NCP-measurement gives: → rms-noise of 12 mK in U and Q

Map of Polarized Intensity combined with southern sky polarization survey at 1.4 GHz (Testori, J. C.; Reich, P.; Reich, W., in The Magnetized Interstellar Medium, 2004 the ultimate goal: all-sky polarization map preliminary version

The l=140° Region HαHα PI HαHα HαHα VTSS & WHAM

The l=140° Region HαHαPI H II regions can be used to: - derive the distance to the origin of polarized emission - derive local synchrotron emissivity towards H II regions > more complicated if there is depolarization and Faraday rotation < apparently, some H II regions do not cause depolarization: - the role of magnetic fields in HII regions? - H II regions with/without B-field?

The l=140° Region B-star dist: ≈ pc S 203 dist: ≈3.8 kpc S 185 dist: ≈210 pc O-star dist: ≈1.2 kpc

The “Depolarization Patch“ observation - low PI and %pol towards inner Galaxy - small scale structure - striking sharp upper and lower boundaries intuitive statements Either caused by: - depolarization along the line-of-sight (depth depolarization) pro: symmetry about Galactic plane total power or - depolarization by a local Faraday screen pro: explains lack of polarized emission from the North-Polar Spur (dist. ≈150 pc)

Data Availability data available within the next two months! then, interpolated data can be downloaded as: J2000 fits format - interpolated U, Q - coverage mask (to retrieve original coverage) - anything else (if requested) Galactic

Future: The DRAO/MPI Rotation Measure Survey frequency range: 1300 MHz – 1800 MHz # channels: about 1,000 – 10,000 fully Nyquist sampled between declination -30° and +90° scans along the Meridian (not drift scanning) rms per 500 MHz band: 0.3 mK observing time: 1.5 years What's next? Digital Polarimetry!

Future: The DRAO/MPI Rotation Measure Survey RM..... RM 25x n e = 0.05 cm -3 L = 150 pc B ║ = μG RM = rad/m 2 Example 1

Future: The DRAO/MPI Rotation Measure Survey n e = 0.04 cm -3 B ║ = 3 μG d = kpc RM = 0.81·n e ·B ║ ·d Example 2

Future: The DRAO/MPI Rotation Measure Survey the observed polarization angle will probably not depend linearly on λ 2 → observed RM depends on frequency! RM-survey products: Stokes U & Q data cubes Stokes I data cube Rotation Measure Synthesis RM-cube (pol. int. vs. Faraday depth)

Summary 1) DRAO 26-m Polarization Survey 2) DRAO/MPI Rotation Measure Survey (data will be released soon) - receiving system currently under development - survey start scheduled for May total observing time required: 1.5 years