  About 10 candidate Halpha emitting galaxies at z = 2.2 have been detected in
a 2.1 um narrow band imaging survey covering an area of 100 sq. arcmin
including the WFPC2 and STIS fields in the Hubble Deep Field South. Six of
these have subsequently been confirmed spectroscopically using ISAAC at the ESO
VLT. Star formation rates of the individual galaxies derived from their Halpha
fluxes are 20-35 Msolar/yr, without any correction for extinction, whereas SFRs
derived from their rest frame UV continuum fluxes are up to a factor of 4 lower
- consistent with lower extinction to Halpha. Velocity dispersions are
typically ~ 100km/s and one galaxy, observed under the most favorable
conditions, shows a rotation curve with a terminal velocity ~ 140 km/s at ~
3kpc radius which is within the range observed for nearby spiral galaxies.
These thus appear to be relatively massive systems at high redshift. Comparison
with the HST NICMOS grism Halpha survey of Yan et al. (1999) reveals little or
no evolution in the Halpha luminosity function between z ~ 1.3 and 2.2. The
inferred star formation rate density of 0.12 Msolar/Mpc^3/yr at z = 2.2 is also
equal to that at z ~ 3-4.5 derived by Steidel et al.(1999) from extinction
corrected UV continuum fluxes.
