PhD15 - Reionisation history and Dark Energy from Cosmic Microwave Background to Cosmic Infrared Background

We invite applications for a PhD position in Cosmology. The successful candidate will be based at LAM, in Marseille. The goal of the thesis is to obtain new constraints on the reionization history and dark energy by combining the Cosmic Infrared Background (CIB) to the Cosmic Microwave Background (CMB)

CIB is the weighted integral of UV heated dust throughout cosmic time. Its distinct frequency-redshift dependence allows to probe a large span of redshifts (0<z<4). In the last few years, anisotropies of the CIB have become an important tracer of large-scale structures. CIB anisotropies have been used to i) probe the cosmology (cf the first detection of the CMB B-modes, by Hanson et al. 2013) and ii) derive information on the physical processes governing the star formation, and galaxy evolution.

In this thesis we propose to use CIB anisotropies detected by the Planck satellite to:

i) Measure the Integrated Sachs Wolf effect by cross-correlating CIB and CMB Planck maps. Using the CIB as a tracer of matter density, the cross-correlation with the CMB will give an alternative probe of dark energy. Theoretical work by Ilic et al. (2011) showed that the CIB, extracted on a large fraction of the sky, may provide the best Integrated Sachs Wolf measurement (in terms of S/N ratio).

ii) Provide unprecedented constraints on the reionization signal encoded in the patchy kinematic Sunyaev-Zel'dovich measurement (kSZ). The project will overcome the two current limitations of kSZ measurements, by (1) combining CIB measurements and multi-frequency sub-millimeter and millimeter observations by Planck, SPT and ACT, to extend the range of scales and frequencies to facilitate the kSZ measurement, and (2) by developing a power spectrum analysis based on physical models of foreground components (CIB, shot noises, tSZ, tSZxCIB) to accurately separate the kSZ from the CIB.

The ultimate goal of the thesis will be to combine the kSZ and ISW constraints with other probes of cosmic reionization and dark energy, to refine the constraints on the cosmological parameters and reionization history. The analysis combining the amplitude of the kSZ at small scale with the polarized power spectra at large scale will translate into constraints on the duration of reionization for a simple single-stage transition as used in ΛCDM.  Combining kSZ and optical depth constraints will further quantify the rapid transition from neutral to ionized medium. Adding the current measurement of UV luminosity functions at high redshift will give more details on the history of reionization. Once a sufficiently accurate history of the reionization has been obtained, the goal will be to improve our knowledge of the rest of the cosmological model, for example by breaking the degeneracy between the competing effects of reionization and the ISW effect (i.e. dark energy) at large scale.

The thesis will involve a number of collaborators (A. Banday from IRAP, S. Ilic from CPT, M. Langer from IAS, M. Tristram from LAL).

Bibliography :
- kSZ: Battaglia N. et al. 2013, ApJ 776, 83 ; George E.M. et al. 2015, ApJ 799, 177
- ISW: Ilic S. et al. 2011, MRNAS 416, 2688
- CIB: Planck collaboration XVIII 2011, A&A 536, 18 ; Planck collaboration  XXX 2014, A&A 571, 30
- Likelihood: Planck collaboration XI 2015, astroph 1507.02704 ; Couchot et al. 2015, astroph 1510.07600