Cosmic Star-Formation Activity at z = 2.2 Probed by H α Emission-Line Galaxies
Cosmic Star-Formation Activity at z = 2.2 Probed by H α Emission-Line Galaxies
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DOI：
10.1093/pasj/63.sp2.s437
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发表时间：
2010-12
影响因子：
2.3
通讯作者：
K. Tadaki;T. Kodama;Y. Koyama;M. Hayashi;I. Tanaka;Chihiro Tokoku University of Tokyo;Subaru Telescope;N. A. O. Japan;T. University
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文献类型：
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作者：
K. Tadaki;T. Kodama;Y. Koyama;M. Hayashi;I. Tanaka;Chihiro Tokoku University of Tokyo;Subaru Telescope;N. A. O. Japan;T. University
我们用斯巴鲁望远镜上的MOIRCS仪器在大观测站原点深度调查北部(Goods-N)区域进行了z=2.2的H-α发射体的窄带试点观测。这次调查的3西格玛极限震级为23.6(NB209)，这相当于56弧度^2的邻接区(不包括较浅的区域)上的3西格玛极限线通量为2.5x10^-17erg S^-1厘米^-2。从这次调查中，我们根据窄带过剩和光度红移，在z=2.2时确定了11个H-α发射体和一个活动星系核。我们获得了其中七个新物体的光谱，其中包括一个活动星系核，所有这些物体都探测到了一条3西格玛以上的发射线。我们估计了单个星系的恒星形成率(SFR)和恒星质量(M_STAR)。平均SFR和M_STAR分别为27.8m太阳yr^-1和4.0×10~(-10)m太阳。它们的特定恒星形成率与它们的恒星质量成反比。对谢克特函数的拟合得到了H-α光度函数，其对数L=42.82，对数Phi=-2.78，α=-1.37。根据H-α光度与恒星形成率之间的Kennicutt关系，估算出该测量体的平均恒星形成率密度为0.31米太阳yr^-1Mpc^-3。我们将我们在Goods-N中z=2.2的H-α发射体与其他场和星团中的窄带线发射体进行了比较，以了解它们的时间演化和环境依赖性。我们发现，在星系团环境中，恒星形成活动从z=2.5迅速减少到z=0.8，而在外场环境中，恒星形成活动变化不大。这一结果表明，星系形成的时间尺度在不同的环境中是不同的，高密度区的恒星形成活动最终会超过低密度区的恒星形成活动，这是高红移时“星系形成偏差”的结果。
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 x 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_star) for individual galaxies. The average SFR and M_star is 27.8M_solar yr^-1 and 4.0 x 10^10M_solar, 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 0.31M_solar yr^-1Mpc^-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.