A hot topic: the 21cm line III Benedetta Ciardi MPA o Differential brightness temperature o Maps are difficult to obtain statistical quantities o Power spectrum: o Angular power spectrum: Some terminology & quantities o Differential brightness temperature o Maps are difficult to obtain statistical quantities o Power spectrum: o Angular power spectrum: Some terminology & quantities depends on e.g.: - underlying density distribution - ionized fraction - Lyalpha distribution - (Loeb & Zaldarriaga 2004) Absorption of CMB flux prior to structure formation density structure Absorption prior to reionization (Loeb & Zaldarriaga 2004; Ali, Bharadwaj & Panday 2005; Barkana & Loeb 2005a; Pillepich, Porciani & Matarrese 2007; Lewis & Challinor 2007) Angular power spectrum (Loeb & Zaldarriaga 2004) Absorption of CMB flux prior to structure formation density structure Pb. Observations at frequencies