The global 21-cm signal in the context of the high-z galaxy luminosity function

We build a new model for the global 21-cm signal that is calibrated to measurements of the high-z galaxy luminosity function (LF) and further tuned to match the Thomson scattering optical depth of the cosmic microwave background, tau(e). Assuming that the z less than or similar to 8 galaxy population can be smoothly extrapolated to higher redshifts, the recent decline in best-fitting values of tau(e) and the inefficient heating induced by X-ray binaries (the presumptive sources of the high-z X-ray background) imply that the entirety of cosmic reionization and reheating occurs at z less than or similar to 12. In contrast to past global 21-cm models, whose z similar to 20 (nu similar to 70 MHz) absorption features and strong similar to 25 mK emission features were driven largely by the assumption of efficient early star formation and X-ray heating, our new models peak in absorption at. similar to 110 MHz at depths similar to-160 mK and have negligible emission components. Current uncertainties in the faint-end of the LF, binary populations in star-forming galaxies, and UV and X-ray escape fractions introduce similar to 20 MHz (similar to 50 mK) deviations in the trough's frequency (amplitude), while emission signals remain weak (less than or similar to 10 mK) and are confined to nu greater than or similar to 140 MHz. These predictions, which are intentionally conservative, suggest that the detection of a 21-cm absorption minimum at frequencies below similar to 90 MHz and/or emission signals stronger than similar to 10mK at nu less than or similar to 140 MHz would provide strong evidence for ` new' sources at high redshifts, such as Population III stars and their remnants.