Title: Young Dusty Starburst Galaxies at z$\sim$2
Author(s): Tomohiro Yoshikawa and MODS team
Abstract:

We present the results of near-infrared multi-object spectroscopic
observations of $K_s$ and Spitzer/MIPS 24$\mu$m selected galaxies
at z$\sim$2.
Our targets are drawn from $K_s$-selected sample of MOIRCS Deep
Survey (MODS) field, which is $\sim 100 {\rm arcmin}^2$ field
centered on HDF-N.
The target galaxies are selected from star-forming BzK (sBzK) down
to $K_{\rm AB}\sim23$, and objects with MIPS 24$\mu$m detection
(>80$\mu$Jy) were observed with high priority.
AGN candidates detected in the ultra deep Chandra image are
excluded from the present samples.
We detected H$\alpha$ emission lines from 23 objects out of the 39
sBzK galaxies with S/N $>$ 3 (within 2$\times$FWHM of line width).
We investigated star formation rate (SFR) of the samples inferred 
from the H$\alpha$ luminosities, comparing with the rest-UV and
infrared luminosities.
Dust extinctions of H$\alpha$ emission lines are estimated from the
extinction derived from a SED fit.
Comparing the dust extinction with the Balmer decrement of the
stacked emission line, we confirmed that the dust extinctions in
the HII regions on average are larger than in the bulk of the stars,
as the relation is known for local starburst galaxies.
We found that a part of sBzKs have larger specific SFR (SSFR,
SFR divided by stellar mass).
Our multi-broad-band SED fitting analysis suggests that these
large-SSFR galaxies are young and dusty galaxies and would be missed
by other selections such as the BX/BM.
These galaxies with the large SSFR ($>10^{-8}$yr$^{-1}$) could 
represent up to ~50\% of the galaxies with M$_\star<10^{10.5}$M$_\odot$
and contribute to the ~75\% of the SFR density of the universe at 
z$\sim$2.