21-cm emission and absorption against the CMB from the region
surrounding a quasar source (lower right corner, in the center of an
HII region), revealed once the IGM is heated above the CMB by soft
X-rays from the quasar. The linear size of the volume is
20h-1 (comoving) Mpc, the angular resolution is 2 arcmin,
and the bandwidth is 1 MHz. The color levels range from -3 &mu Jy to 3
&mu Jy per beam. The dark contour demarcates the absorption ring. The
quasar turns on at z = 8.5 with an ionizing photon luminosity of
1057 photons s-1, and is observed after 10
Myr. The temperature of the IGM beyond the light radius is assumed to
be TK = 26 mK (1+z)2 = 2.3 K < TCMB.
(From Tozzi et al. 2000.)