Optical spectra of 14 emission-line galaxies representative of the 1999 NICMOS parallel grism H \alpha survey of McCarthy et al .
are presented .
Of the 14 , 9 have emission lines confirming the redshifts found in the grism survey .
The higher resolution of our optical spectra improves the redshift accuracy by a factor of 5 .
The [ O II ] /H \alpha values of our sample are found to be more than two times lower than expected from Jansen et al .
This [ O II ] /H \alpha ratio discrepancy is most likely explained by additional reddening in our H \alpha -selected sample [ on average , as much as an extra E ( B-V ) = 0.6 ] , as well as to a possible stronger dependence of the [ O II ] /H \alpha ratio on galaxy luminosity than is found in local galaxies .
The result is that star formation rates ( SFRs ) calculated from [ O II ] \lambda 3727 emission , uncorrected for extinction , are found to be on average 4 \pm 2 times lower than the SFRs calculated from H \alpha emission .
Classification of emission-line galaxies as starburst or Seyfert galaxies based on comparison of the ratios [ O II ] /H \beta and [ Ne III ] \lambda 3869/H \beta is discussed .
New Seyfert 1 diagnostics using the H \alpha line luminosity , H -band absolute magnitude , and H \alpha equivalent widths are also presented .
One galaxy is classified as a Seyfert 1 based on its broad emission lines , implying a comoving number density for Seyfert 1s of 2.5 ^ { +5.9 } _ { -2.1 } ~ { } \times 10 ^ { -5 } Mpc ^ { -3 } .
This commoving number density is a factor of 2.4 ^ { +5.5 } _ { -2.0 } times higher than estimated by other surveys .