Hydrogen recombination line masers at the epochs of recombination and reionization

We model the physical properties of masing hydrogen recombination lines at z(rc) similar to 1000. We find that if small-scale, strongly overdense regions exist, then maser action is possible in this phase of cosmological evolution owing to the expansion of the universe and the low ambient temperature at decoupling. Partial-line absorption of n alpha similar to 60 maser radiation can occur at the epoch of reionization (z(ri) similar to 10-50). The paths along which maser amplification is sustained during the epoch of recombination are assumed to be associated with the strong density perturbations required for the development of ionizing sources at z(ri). The combined spectrum can be observed at around 10-100 MHz (z = 0) and provides information on the power spectrum, H-0, q(0), and the evolution of H II regions during the epoch of reionization. The flux level is similar to 40 mu Jy, depending on the magnitude of the perturbation, with brightness temperatures of greater than 10(7) K. The Square Kilometer Array (SKAI) would have the sensitivity to observe these features. During reionization n alpha similar to 120, maser lines can also be produced along the edges of the early H II regions. Observations of these lines require telescopes that are able to operate below 80 MHz with a sensitivity of 1 mu Jy at an angular size of similar to 1 ''. Although these requirements offer many challenges for the development of suitable ground-based and space-based telescopes, we indicate in this paper that such observations can be very important to understanding the physics and cosmology of these early epochs. Line observations of this sort have the potential to probe the complicated physical processes occurring in the nonlinear regime that is not directly accessible to continuum instruments such as COPE and its successors MAP and the Planck Surveyor.