Near-Infrared Emission Line Searches for High-Redshift Galaxies

In this article I review recent developments in near-infrared emission line searches for star-forming galaxies at high redshift. Using the J-, H& K-bands we can potentially chart the history of star formation over the range 1 < z < 5 using the prominent rest-optical nebular emission lines alone, filling in the “redshift desert” at z ∼ 1 − 3 where most common emission lines lie outside the optical bands. Studying the rest-frame optical at z ∼ 2 also allows a fair comparison to be made with the local Universe – the rest-optical lines are vastly more robust to extinction by dust than the rest-UV, with the resonantly-scattered Lyα line particularly unreliable. I discuss the recent history of near-infrared emission-line searches using narrow-band imaging and spectroscopy, and look to the future in this era of 10m telescopes: such work gives us the potential to push to z > 10, the next frontier in the Hy-Redshift Universe.