A Wide Area Survey for High-redshift Massive Galaxies. II. Near-infrared
  Spectroscopy of BzK-selected Massive Star-forming Galaxies
  Results are presented from NIR spectroscopy of a sample of BzK-selected,
massive star-forming galaxies (sBzKs) at 1.5<z<2.3 that were obtained with
OHS/CISCO at Subaru and with SINFONI at VLT. Among the 28 sBzKs observed, Ha
emission was detected in 14 objects, and for 11 of them the [NII]6583 was also
measured. Multiwavelength photometry was also used to derive stellar masses and
extinction parameters, whereas Ha and [NII] have allowed us to estimate SFR,
metallicities, ionization mechanisms, and dynamical masses. In order to enforce
agreement between SFRs from Ha with those derived from rest-frame UV and MIR,
additional obscuration for the emission lines (that originate in HII regions)
was required compared to the extinction derived from the slope of the UV
continuum. We have also derived the stellar mass-metallicity relation, as well
as the relation between stellar mass and specific SFR, and compared them to the
results in other studies. At a given stellar mass, the sBzKs appear to have
been already enriched to metallicities close to those of local star-forming
galaxies of similar mass. The sBzKs presented here tend to have higher
metallicities compared to those of UV-selected galaxies, indicating that NIR
selected galaxies tend to be a chemically more evolved population. The sBzKs
show specific SFRs that are systematically higher, by up to ~2 orders of
magnitude, compared to those of local galaxies of the same mass. The empirical
correlations between stellar mass and metallicity, and stellar mass and
specific SFR are then compared with those of population synthesis models
constructed either with the simple closed-box assumption, or within an infall
scenario. Within the assumptions that are built-in such models, it appears that
a short timescale for the star-formation (~100 Myr) and large initial gas mass
appear to be required if one wants to reproduce both relations simultaneously.
