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Cosmic microwave background modeling from Planck all sky survey and NANTEN2 super CO survey

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Contens

Members

  • Yasuo Fukui (Professor, Department of Astrophysics, Nagoya University, PI)
  • Takeshi Okuda (Assistant Professor, Department of Astrophysics, Nagoya University)
  • Tsutomu Takeuchi (Lecturer, Department of Astrophysics, Nagoya University)
  • Kiyotomo Ichiki (Assistant Professor, Department of Astrophysics, Nagoya University)
  • Shuichiro InutsukaiProfessor, Department of Astrophysics, Nagoya Universityj
  • Hiroyuki MaezawaiAssistant Professor, Solar-Terrestrial Environment laboratory, Nagoya Universityj

Overseas collaborators

  • J.-L. Puget
  • F. Boulanger
  • J.-P. Bernard

Background of Research Project

Support for the formation of the Universe via the Big Bang 13.7 Gyrs ago is found through an enormous diversity of data. The recession of galaxies (the Hubble law), abundance of light elements, and the cosmic microwave background (CMB) radiation all offer firm observational evidence for the Big Bang. It is now imperative to experimentally test and explore the physics of inflation, the most dramatic rapid expansion of the Universe over 30 orders of magnitude, immediately following the Big Bang. Gravitational waves associated with the inflation have left an imprint on the polarization of the CMB ? the so-called B-mode signal, and the detection of the B-mode polarization in the CMB holds the most potential for observational exploration of the inflation epoch.

Crucial for elucidating the B-mode polarization is a complete understanding of foreground emission. As the B-mode signal is so much weaker than the foreground Galactic polarized emission, it is immediately overwhelmed by continuum emission from dust in the Interstellar medium (ISM), at frequencies of 100 GHz and higher and which must be removed using alternative techniques, such as that described in this proposal.


Importance and Necessity of this Project and its Expected Impact upon the Target Field of Research

The detection of the B-mode signal has become the most crucial for modern cosmology. The majority of ongoing cosmological experiments, including the Planck project, are focused towards achieving this goal. Realizing this objective is entirely contingent upon accurate estimates of the foreground polarized emission, originating primarily from dust oriented along the magnetic field lines at a frequency of 100GHz or higher as discussed by the Task Force on Cosmic Microwave Background Research, July 11, 2005. The reliable detection of the B-mode polarization will have far-reaching impacts on a number of fundamental physical sciences including cosmology, astronomy, and particle physics.


Research Objectives and Targeted Goals of this Project

The primary goal for the proposed research is the detection of B-mode polarization across larger angular scales than the Planck CMB data. Complimented with additional ground-based, experiments to provide small-scale component, these data will be absolutely key in an observational test of the inflation Universe. Essential to this goal is an understanding of the foreground polarization generated by the Galactic aligned dust in the ISM, which otherwise completely obscures the background B-mode polarization signal. These data are to be obtained from the successful Planck mission, launched in 2009. Polarization of the foreground Galactic dust is generated by interaction of elongated dust with large and small-scale magnetic fields, which are themselves strongly coupled with the dense and diffuse ISM. As the densest phase of the ISM has been shown to correlate very well with molecular emission, a complete knowledge of the morphological structure of the densest phase of molecular gas throughout the entire of the Galaxy is necessary for the success of this B-mode project.


Fig.1 (1) 9-band (30-900GHz) synthesized all sky image taken with Planck satellite (courtesy of ESA). (2) A close-up of a high galactic-latitude region showing the CMB with relatively little contamination by Galactic foreground material. (3) NANTEN image of Orion molecular clouds in CO. (4) Planck image of Orion molecular clouds.

Presently, no suitable whole-sky survey of the Galactic molecular emission exists: the largest and most complete survey in existence is the NANTEN Galactic plane CO survey (NGPS ver.1; 110 Million points) which consists of under-sampled CO data at 4-8 arcmin grid, with a 2.6 arcmin beam.


Fig.2 Schematic image of the anisotropy in the CMB. Extracting the B-mode polarization induced by the primordial gravitational waves requires a precise separation complicating processes; scattering during the Epoch of Reionization, Gravitational Lensing, and Galactic synchrotoron and scattering by dust.

We intend to undertake a "super CO survey", consisting of 20 million observed points as an extension to the NGPS, with the NANTEN2 4m telescope located at 4865m high in Atacama in Chile. The superb atmospheric condition of the site will allow rapid on-the-fly (OTF) sky survey of complete sampling in 2-3 yrs covering 70% of the sky in the J=1-0 transitions of 12CO, 13CO and C18O molecules in a range of 109-115 GHz, best probes of the dense ISM. This survey, named NASCO [NANTEN Super CO Survey as Legacy] will provide, first and foremost, the most comprehensive and detailed dataset of the morphology and velocity distribution of the dense ISM within the Galaxy.

The foreground Galactic polarization can be derived from dust and ISM magneto-hydrodynamic models developed by the Planck consortium. The resulting Galactic polarization model will be compared with the Planck polarization data, and the modeling parameters will be iterated until a satisfactory match between model and data is achieved. This process will produce the most accurate description of the polarized CMB emission, will reveal the morphological structure of the B-mode polarization, and answer the fundamental cosmological question on the occurrence and rate of the inflation of the very early Universe.

An important and useful byproduct of this process is the high-resolution and high-accuracy sampling of the Galactic magnetic field, which will make far-reaching contributions to this field of study. NASCO will have further-reaching application when combined with ancillary datasets that trace additional phases of the ISM. Such data will become available from international and in-development facilities: the higher resolution HI datasets (SKA), the low-frequency recombination lines and the early-epoch HI Universe (LOFAR) etc. When combined with these, and other datasets, NASCO will be integrated into a full description of the multi-phase gas component and with the dust component of the near and far Universe. We therefore expect that the proposed research will bring about a number of important breakthroughs in the ISM physics of our Galaxy and Universe, across both large and small scales, and will form a precious Legacy for the world-wide astronomical community.


Fig.3 CMB polarization angular power spectra and estimated sensitivity of various CMB experiments including Planck. Solid wavy curves are predicted B-mode polarization induced by primordial gravitational waves; three values of tensor-to-scalar ratio r are presented (0.3, 0.1, and 0.03). The dash-dotted curve is E-mode polarization by density perturbation and the broken line is B-mode due to the distortion of E-modes by gravitational lensing.

We here note that the Planck specification indicates a possibility of CO line contamination in the 100GHz band covering 82GHz-118GHz and also in two more bands covering the J=2-1 and 3-2 CO lines. This possible contamination should be carefully verified by the CO data and strengthen the importance of the proposed NASCO CO data.


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(c)Copyright 2006,Radio Astronomy Laboratry, Department of Physics, Graduate School of Science, Nagoya University.