Galactic Radioemission – a problem for precision cosmology ?
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Transcript of Galactic Radioemission – a problem for precision cosmology ?
Galactic Radioemission – Galactic Radioemission – a problem for precision cosmology ?a problem for precision cosmology ?
Absolute Temperatures at Short CM-Waves with
a Lunar Radio Telescope
Wolfgang Reich
Max-Planck-Institut für Radioastronomie
Bonn
Bremen 22./23.3.2005
Summary and ConclusionSummary and Conclusion
Scientific needs:Scientific needs: absolutely calibrated sky surveys absolutely calibrated sky surveys in I and PI between ~5-15 GHz in I and PI between ~5-15 GHz
Technical needs:Technical needs: 10m/15m meridian telescope 10m/15m meridian telescope operating at 3-5 frequenciesoperating at 3-5 frequencies
Location:Location: backside of the moon close to backside of the moon close to equator (+/- ~5° latitude) equator (+/- ~5° latitude)
Absolutely Calibrated Absolutely Calibrated All-Sky Radio Continuum All-Sky Radio Continuum
SurveysSurveys
408 MHz408 MHzHaslam et al. Haslam et al.
HPBW = 51’, HPBW = 51’, T = 2K T = 2K
1420 MHz1420 MHzReich et al. Reich et al.
HPBW = 35’, HPBW = 35’, T= 50mK T= 50mK
Spectral Index ßSpectral Index ß 408 MHz / 1420 MHz 408 MHz / 1420 MHz
= 2.4 (blue) – 3.0 (red) = 2.4 (blue) – 3.0 (red)Reich et al.Reich et al.
ß
Galactic emissionGalactic emission
mixture of synchrotron ß = 2.4…3.2 mixture of synchrotron ß = 2.4…3.2 + thermal emission ß = 2.1 + thermal emission ß = 2.1
anomalous dust: 10 GHz – 30 GHz ?anomalous dust: 10 GHz – 30 GHz ? component separation difficult component separation difficult absolutely calibrated surveys at absolutely calibrated surveys at
several frequencies neededseveral frequencies needed extrapolation to CMB-Frequencies extrapolation to CMB-Frequencies
uncertainuncertain
Absolute Calibration Sequence for Absolute Calibration Sequence for Total IntensitiesTotal Intensities
Absolute skyhorn measurements Absolute skyhorn measurements ~10°/15° angular resolution~10°/15° angular resolution
calibration of medium angular calibration of medium angular resolution all-sky surveysresolution all-sky surveys
calibration of high resolution maps calibration of high resolution maps e.g. Galactic plane surveyse.g. Galactic plane surveys
Absolute „3K“ Absolute „3K“ MeasurementsMeasurements
largely uncertain largely uncertain below below λλ ~ 1cm ~ 1cm
Available surveys
anomalous dust
+212 µK
1.41 GHz Dwingeloo polarization surveyBrouw & Spoelstra, 1976
absolutely calibrated
Anticorrelation of I/ PI with Galactic latitude
(Reich et al. 1990, Duncan et al. 1999)
24° x 9° section centered at l , b = 162°,0°
1.4 GHz Effelsberg Medium Latitude Survey (EMLS)
I
PI
Absolute Polarization Calibration: Absolute Polarization Calibration: „A Must„A Must“ for Galactic Emission“ for Galactic Emission
Vector additionVector addition for polarisation for polarisation scalar addition for total intensityscalar addition for total intensity
PI = (UPI = (U22 + Q + Q22))1/2 1/2 measuredmeasured ΦΦ = 0.5 atan (U/Q) = 0.5 atan (U/Q) PIPIabsolute absolute = ((U+U= ((U+Uoffoff))22 +(Q+Q +(Q+Qoffoff))22))1/21/2
ΦΦ = 0.5 atan (U = 0.5 atan (U+U+Uoffoff))/(Q/(Q+Q+Qoffoff))
U/Q may be positive or negativeU/Q may be positive or negative
Rotation Measure: RM [rad/m2] RM = 0.81 ne [cm-3] B||[G] L[pc], [rad] = RM 2 [m]
ForegroundForeground
BackgroundBackground
Faraday Screen
High latitude field with dominating large scale emission. 20% of pixel exceed 3xr.m.s.-noise FS fraction.
Angle statistics for G109+73
relative Effelsberg angles: mean -9.8°, rms 47°
absolute Eff.+DRAO angles:mean -36.5°, rms 7°
need for RM determination
Field reversal at high latitudes ?
5 GHz RX for large scale polarization mapping at the Urumqi (China)
25m telescope(same 9.4‘ beam as 1.4 GHz EMLS)
MPIfR 5 GHz RX
5 GHz Urumqi observations of W1 (NGC7822)
PI towards W1 (on relative level)
Distance = 850 pc
Observed PI =
PIFG– (PIFG + PIBG)
small Faraday effects in the ISM at 5 GHz
I
PI
Green Bank 300-ft10m/15m telescope
3-5 RX out of 5–15 GHz band El-range ~180°backside of the Moon close to equator (+/- ~5° latitude)duration > 2 years ?
Green Bank 300ft
IAR 30m
The End
26-m telescope at DRAO/Canada: absolute polarization measurements
> -30° at 1.4 GHz first phase done (undersampled)
Thesis Maik Wolleben (2005)
30-m telescope at Villa Elisa/Argentina
I + PI survey at 1.4 GHz
Selected surveys