z~2大质量星系的多波长研究。I.恒星形成与星系成长
Multiwavelength study of massive galaxies at z~2. I. Star formation and galaxy growth
摘要：
通过对来自大天文台起源深度巡天（Great Observatories Origins Deep Survey）的1.4<z<2.5、K_{Vega} <22的大质量星系样本进行检查，我们比较了斯皮策望远镜在中红外和远红外、亚毫米波、射电和静止帧紫外波长的测光，以检验不同恒星形成率（SFR）示踪剂之间的一致性，并探索对星系组装的影响。对于中等光度的z~2星系（L_{8um} <10^{11}L_sun），我们发现，基于局域光度相关的多波长数据可以一致地估计SFR。然而，20- 30%的大质量星系，以及几乎所有L_{8um} >10^{11}L_sun的星系，都显示出中红外过量，这可能是由于存在被遮蔽的活动核，如配套论文所示。对于24 μ m探测到的星系，恒星质量和SFR之间存在紧密的近似线性关系。对于一个给定的质量，在z=2时的SFR比在z=1和z=0时的恒星形成星系的SFR分别大4倍和30倍。典型的z=2的超亮红外星系（ultraluminous infrared galaxies，ULIRGs）对紫外线相对“透明”，它们的活动寿命很长（约4亿年），不像本地ULIRGs和高红移亚毫米选择星系。ULIRGs是z=2的大质量星系中恒星形成的常见模式，高占空比表明，主要合并不是这一活动的主要触发因素。目前的星系形成模型低估了质量-SFR相关的归一化因子约为4，ULIRGs的空间密度为一个数量级，但对于z>1.4的静止星系给出了更好的一致性。
英文摘要：
Examining a sample of massive galaxies at 1.4<z<2.5 with K_{Vega}<22 from the Great Observatories Origins Deep Survey, we compare photometry from Spitzer at mid- and far-IR, to submillimeter, radio and rest-frame ultraviolet wavelengths, to test the agreement between different tracers of star formation rates (SFRs) and to explore the implications for galaxy assembly. For z~2 galaxies with moderate luminosities(L_{8um}<10^{11}L_sun), we find that the SFR can be estimated consistently from the multiwavelength data based on local luminosity correlations. However,20--30% of massive galaxies, and nearly all those with L_{8um}>10^{11}L_sun, show a mid-IR excess which is likely due to the presence of obscured active nuclei, as shown in a companion paper. There is a tight and roughly linear correlation between stellar mass and SFR for 24um-detected galaxies. For a given mass, the SFR at z=2 was larger by a factor of ~4 and ~30 relative to that in star forming galaxies at z=1 and z=0, respectively. Typical ultraluminous infrared galaxies (ULIRGs) at z=2 are relatively 'transparent' to ultraviolet light, and their activity is long lived (~400 Myr), unlike that in local ULIRGs and high redshift submillimeter-selected galaxies. ULIRGs are the common mode of star formation in massive galaxies at z=2, and the high duty cycle suggests that major mergers are not the dominant trigger for this activity.Current galaxy formation models underpredict the normalization of the mass-SFR correlation by about a factor of 4, and the space density of ULIRGs by an orderof magnitude, but give better agreement for z>1.4 quiescent galaxies.
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