Cosmic background dipole measurements with the Planck-high frequency instrument

Abstract

This paper discusses the Cosmic Background (CB) dipole observations in the framework of the Planck mission. Dipole observations can be used in three ways: (i) It gives a measurement of the peculiar velocity of our Galaxy which is an important observation for large-scale structure formation models. (ii) Measuring the dipole can give information on the monopole that can be in some cases hard or impossible to measure due to large foreground contamination or instrumental design. (iii) The dipole can be an ideal absolute calibrator, easily detectable in cosmological experiments. Here, we study the accuracy of the Planck-HFI calibration using the Cosmic Microwave Background (CMB) dipole measured by COBE as well as the Earth orbital motion dipole. We show that for HFI we can reach a relative calibration between rings of about 1% and an absolute calibration better than 0.4% for the CMB channels. In the end, the absolute calibration will be limited by the uncertainties on the CMB temperature. We also show that Planck will be able to measure the CMB dipole direction at better than 1.7 arcmin and improve the accuracy of the amplitude. Second, we investigate the detection of the Cosmic Far-Infrared Background (FIRB) dipole. Measuring this dipole could give a new and independent determination of the FIRB for which a direct determination is quite difficult. We show that such a detection would require Galactic dust emission removal to better than 1%, which would be very hard to achieve.