The Cosmic Microwave Background (CMB), just like the HI 21 cm radiation, constitutes a privileged witness of the evolution of our universe during and after the epoch of reionization. This parallelism between the two radiation fields is also reflected in the fact that cosmological events leave different (but often complementary) signatures on both photon fields. In fact, there exists a number of physical channels of interaction between the CMB radiation with electrons, atoms, ions and gravitational potentials during and after the epoch of reionization: these strongly motivate a joint study of the CMB and future HI 21 cm data. In this context, we also highlight the existing parallelism between problems addressed in CMB analysis and problems foreseen in future HI 21 cm observations, in many of which the Spanish cosmological community has been deeply involved during the last decade.

The authors acknowledge partial support from the Spanish Ministerio de Economía y Competitividad (MICINN) through projects AYA2013-48623-C2-2, AYA2007-68058-C03-01, AYA2010-21766-C03-02, AYA2012-30789, and the Consolider-Ingenio project CSD2010-00064 (EPI: Exploring the Physics of Inflation). We also acknowledge the support of the Ramón y Cajal fellowship (RyC 2011 148062) awarded by the Spanish MICINN and the Marie Curie Career Integration Grant (CIG 294183).

Peer reviewed