The Nature of Compact Galaxies in the Hubble Deep Field. II. Spectroscopic Properties and Implications for the Evolution of the Star Formation Rate Density of the Universe
The Nature of Compact Galaxies in the Hubble Deep Field. II. Spectroscopic Properties and Implications for the Evolution of the Star Formation Rate Density of the Universe
复制标题
哈勃深场致密星系的性质。
DOI：
10.1086/304797
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
N. Vogt
中科院分区：
文献类型：
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作者：
R. Guzmán;J. Gallego;D. Koo;A. Phillips;J. Lowenthal;S. Faber;G. Illingworth;N. Vogt
我们对哈勃深场侧翼场中 51 个红移 z < 1.4 和视星等 I814 < 23.74 的致密场星系进行了光谱研究。这些星系是紧凑的，因为它们具有较小的表观半光半径（r1/2 ≤ 0.″5）和高表面亮度（μI814 ≤ 22.2 mag arcsec-2）。凯克望远镜拍摄的光谱显示了 88% 样品中的发射线，而其余 12% 中仅显示了吸收线。发射线轮廓大致呈高斯分布，速度宽度范围从测量极限 σ ~ 35 km s-1 到 150 km s-1。静止框架 [O II] λ3727 等效宽度范围为 5 至 94 Å，产生的恒星形成速率 (SFR) 约为 0.1 至 14 M☉ yr-1。对各种线诊断图的分析表明，约 60% 的致密发射线星系具有年轻恒星形成 H II 星系的速度宽度、激发、Hβ 光度、恒星形成率和质光比特征。剩下的 40% 形成了一种更加异质的演化星暴，类似于当地的星暴盘星系。我们发现，虽然 z > 0.7 处的致密星系每单位质量的恒星形成率与 z < 0.7 处的致密星系相似，但它们的质量平均要高出约 10 倍。我们的样本表明，在 z = 0.55 时，全局共动恒星形成率密度的下限为 ~0.004 M☉ yr-1 Mpc-3，在 z = 0.85 时为 ~0.008 M☉ yr-1 Mpc-3（假设 Salpeter IMF，H0 = 50 km s-1 Mpc-1，q0 = 0.5）。与以类似方式选择的局部致密星系样本的估计值相比，这些值支持了宇宙历史，其中恒星形成率密度从 z = 1 到今天下降了约 10 倍。通过与场星系星等受限样本得出的恒星形成率密度进行比较，我们得出结论，致密发射线星系虽然只占一般场星系群的约 20%，但在 0.4 < z < 1 时对宇宙全局恒星形成率的贡献可能高达约 45%。
We present a spectroscopic study of 51 compact field galaxies with redshifts z < 1.4 and apparent magnitudes I814 < 23.74 in the flanking fields of the Hubble Deep Field. These galaxies are compact in the sense that they have small apparent half-light radii (r1/2 ≤ 0.″5) and high surface brightnesses (μI814 ≤ 22.2 mag arcsec-2). The spectra, taken at the Keck telescope, show emission lines in 88% of our sample, and only absorption lines in the remaining 12%. Emission-line profiles are roughly Gaussian with velocity widths that range from the measurement limit of σ ~ 35 km s-1 to 150 km s-1. Rest frame [O II] λ3727 equivalent widths range from 5 to 94 Å, yielding star formation rates (SFRs) of ~0.1 to 14 M☉ yr-1. The analysis of various line diagnostic diagrams reveals that ~60% of compact emission-line galaxies have velocity widths, excitations, Hβ luminosities, SFRs, and mass-to-light ratios characteristic of young star-forming H II galaxies. The remaining 40% form a more heterogeneous class of evolved starbursts, similar to local starburst disk galaxies. We find that, although the compact galaxies at z > 0.7 have similar SFRs per unit mass to those at z < 0.7, they are on average ~10 times more massive. Our sample implies a lower limit for the global comoving SFR density of ~0.004 M☉ yr-1 Mpc-3 at z = 0.55, and ~0.008 M☉ yr-1 Mpc-3 at z = 0.85 (assuming Salpeter IMF, H0 = 50 km s-1 Mpc-1, and q0 = 0.5). These values, when compared to estimates for a sample of local compact galaxies selected in a similar fashion, support a history of the universe in which the SFR density declines by a factor ~10 from z = 1 to today. From the comparison with the SFR densities derived for magnitude-limited samples of field galaxies, we conclude that compact emission-line galaxies, though only ~20% of the general field population, may contribute as much as ~45% to the global SFR of the universe at 0.4 < z < 1.