(Proposal ID) S10A-025

(PI) Tadaki, Ken-ichi

(Proposal Title)
Spectroscopic follow-up on the narrow-band Halpha emitter candidates at z=2.2

(Abstract)
Currently, most of the samples of galaxies at z > 2 are selected on the basis 
of rest-frame UV light and we inevitably miss dusty galaxies. H alpha is a 
much better indicator of star formation activity as itfs much less affected 
by dust extinction or metallicity dependence, and we have been in need for a 
large systematic H alpha survey of distant galaxies to probe cosmic star 
formation history. In S08A, we have conducted a pilot survey of un-biased 
H alpha emitters survey at z=2.2 in GOODS-North field using our purpose-made 
narrow-band filter NB209 on MOIRCS, and we have successfully detected 64 
H alpha emitter candidates down to 9 M_sun/yr. We here propose to make a 
follow-up spectroscopic observation of these emitters with MOIRCS in MOS mode. 
We will securely discriminate H alpha emitters at z=2.2 from other contaminant 
lines, and measure accurate redshifts and star formation rates of them. We 
stress that making a sample of H alpha emitter candidates initially with deep 
NB imaging and then confirm them with multi-object spectroscopy is the unique, 
best strategy to obtain an un-biased, complete, deep and large sample of H 
alpha emitters at high redshift, and our sample of H alpha emitters at z=2.2 
will enable us for the first time to measure star formation activity at this 
peak epoch of galaxy formation.