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Measuring the Cosmic Optical Background

Measuring the Cosmic Optical Background. DECam Community Workshop 18-19 Aug. 2011, Tucson, Arizona. Nobuyuki Ienaka University of Tokyo. Cosmic Optical Background (COB).

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Measuring the Cosmic Optical Background

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  1. Measuring the Cosmic Optical Background DECam Community Workshop 18-19 Aug. 2011, Tucson, Arizona Nobuyuki Ienaka University of Tokyo

  2. Cosmic Optical Background (COB) • COB = the diffuse (unresolved) radiation coming from outside the Galaxy and observed in optical wave bands. Figure from Bethermin+2010 HST (Bernstein 2007)

  3. Foreground Emission • The major difficulty in observing the COB is strong foreground emission. • terrestrial airglow：atmospheric emission >1,000 ICOB • zodiacal light：scattered sunlight by interplanetary dust>100 ICOB • Galactic stars：can be resolved by deep imaging>30 ICOB • Diffuse Galactic light: scattered starlight by interstellar dust>1 ICOB

  4. Current Observations • Bernstein et al. (2002, 2005, 2007) • Blank-field observation with the HST/WFPC2 • Free from the terestrialairglow, but have a difficulty in the zodiacal lightsubtraction • Matsuoka et al. (2011) • Re-analysis of the Pioneer 10/11 data • Observation at the heliocentric distances > 3.3 AU (i.e., outside the zodiacal light clouds)

  5. Current Observations • Bernstein et al. (2002, 2005, 2007) • Blank-field observation with the HST/WFPC2 • Free from the terestrialairglow, but have a difficulty in the zodiacal lightsubtraction • Matsuoka et al. (2011) • Re-analysis of the Pioneer 10/11 data • Observation at the heliocentric distances > 3.3 AU (i.e., outside the zodiacal light clouds) HST (Bernstein 2007) Pioneer10/11 (Matsuoka+2011)

  6. Another approach • Dark cloud method(proposed by Mattila 1976) • Comparing the brightness measured at two lines of sight We can remove the airglow and the zodiacal light by this method. However, Diffuse Galactic Light (DGL) cannot be removed. Diffuse Galactic Light Zodiacal Light COB Airglow

  7. How to remove the DGL • We use a correlation between the DGL and Far-IR emission Toward a nearby sky Toward a dark cloud Optical(DGL) 0.65um ICIB Optical(DGL) 0.65um IRAS 100um IRAS 100um Idiffuse= IDGL + ICOB = aDGL (I100um – ICIB) + ICOB The gap between two intersection correspond to the COB brightness

  8. Result • Result from our observation (2 deg2 ,limiting mag ~ 19mag) only an upper limit was obtained HST To improve the accuracy of the measurement, we have to observe a wide area (increase independent data points) with sufficient deepness ( >20mag, for Galactic star subtraction) at high Galactic latitude (less DGL). →　DECam’s data could beuseful for our study ! Pioneer10/11

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