  We present results from a near-infrared narrow-band survey of emission-line
galaxies at z=2.23, using the Wide Field Camera on the United Kingdom Infrared
Telescope. The H2S1 narrow-band filter (lambda_c=2.121um) we employ selects the
H-alpha emission line redshifted to z=2.23, and is thus suitable for selecting
'typical' star forming galaxies and active galactic nuclei at this epoch. The
pilot study was undertaken in the well studied Cosmological Evolution Survey
field (COSMOS) and is already the largest near-infrared narrow-band survey at
this depth, with a line flux limit of F(H-alpha)~10^-16 erg/s/cm^2 over 0.60
square degrees, probing ~220x10^3 Mpc^3 (co-moving) down to a limiting star
formation rate of 30 M_sun/yr (3sigma). In this paper we present the results
from our pilot survey and evaluate the H-alpha luminosity function and estimate
the clustering properties of H-alpha emitters at z=2.23 from 55 detected
galaxies. The integrated luminosity function is used to estimate the volume
averaged star formation rate at z=2.23: SFRD = 0.17^{+0.16}_{-0.09}
M_sun/yr/Mpc^3 for L(H-alpha) > 10^42 erg/s. For the first time, we use the
H-alpha star-formation tracer to reliably constrain SFRD out to z=2.23
demonstrating the rapid increase in SRFD out to this redshift as well as
confirming the flattening in SFRD between z~1-2. In addition to the luminosity
distribution, we analyse the clustering properties of these galaxies. Using the
2-point angular correlation function, we estimate a real space correlation
length of r_0= 4.2^{+0.4}_{-0.2} h^-1 Mpc. In comparison to models of
clustering which take into account bias evolution, we estimate that these
galaxies are hosted by dark matter halos of mass M_halo ~ 10^12 M_sun
consistent with the progenitors of the Milky Way.
