We present a pilot narrow-band survey of H \alpha emitters at z = 2.2 in the Great Observatories Origins Deep Survey North ( GOODS-N ) field with MOIRCS instrument on the Subaru telescope .
The survey reached a 3 \sigma limiting magnitude of 23.6 ( NB209 ) which corresponds to a 3 \sigma limiting line flux of 2.5 \times 10 ^ { -17 } erg s ^ { -1 } cm ^ { -2 } over a 56 arcmnin ^ { 2 } contiguous area ( excluding a shallower area ) .
From this survey , we have identified 11 H \alpha emitters and one AGN at z = 2.2 on the basis of narrow-band excesses and photometric redshifts .
We obtained spectra for seven new objects among them , including one AGN , and an emission line above 3 \sigma is detected from all of them .
We have estimated star formation rates ( SFR ) and stellar masses ( M _ { \mathrm { star } } ) for individual galaxies .
The average SFR and M _ { \mathrm { star } } is 27.8 M _ { \odot } yr ^ { -1 } and 4.0 \times 10 ^ { 10 } M _ { \odot } , respectivly .
Their specific star formation rates are inversely correlated with their stellar masses .
Fitting to a Schechter function yields the H \alpha luminosity function with log L = 42.82 , log \phi = - 2.78 and \alpha = - 1.37 .
The average star formation rate density in the survey volume is estimated to be 0.31 M _ { \odot } yr ^ { -1 } Mpc ^ { -3 } according to the Kennicutt relation between H \alpha luminosity and star formation rate .
We compare our H \alpha emitters at z = 2.2 in GOODS-N with narrow-band line emitters in other field and clusters to see their time evolution and environmental dependence .
We find that the star formation activity is reduced rapidly from z =2.5 to z =0.8 in the cluster environment , while it is only moderately changed in the field environment .
This result suggests that the timescale of galaxy formation is different among different environments , and the star forming activities in high density regions eventually overtake those in lower density regions as a consequence of “ galaxy formation bias ” at high redshifts .