Discovery of Nine Lyα Emitters at Redshift z ~ 3.1 Using Narrowband Imaging and VLT Spectroscopy
Discovery of Nine Lyα Emitters at Redshift z ~ 3.1 Using Narrowband Imaging and VLT Spectroscopy
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使用窄带成像和 VLT 光谱发现红移 z ~ 3.1 处的九个 Lyα 发射体
DOI：
10.1086/308925
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
G. Jacoby
中科院分区：
文献类型：
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作者：
R. Kudritzki;K. C. Freeman;M. Capaccioli;H. Ford;Roberto H. Méndez;O. Gerhard;J. Feldmeier;R. Ciardullo;M. Arnaboldi;G. Jacoby
窄带成像探测旨在探测处女座星系团内行星星云的5007ä[O III]线发出的微弱辐射，还探测到高红移的z~3.1Lyα发射体。本文报道了用甚大望远镜1单元的焦散射光谱仪在z=3.13时获得的9个Lyα发射体的光谱鉴定结果，它们的通量在2×10~(-17)~2×10~(-16)ergs cm~(-2)S~(-1)之间。这些高红移天体的光谱显示出窄而孤立的Lyα发射，具有非常微弱(通常未被检测到)的连续体，表明有很大的等效宽度。在我们的光谱中看不到其他特征。我们的Lyα发射器与胡、考伊和他的同事在1998年发现的非常相似。对于H_0=70公里S~(-1)Mpc~(-1)和q_0=0·5(ΩΛ=0)的平坦宇宙，最亮光源的Lyα光度为1·7×10~(-9)L☉，Lyα发射体在所搜索的体积内的平移空间密度为5×10~(-3)Mpc~(-3)。利用简单的群体合成模型，在假设这些源是恒星形成区的情况下，我们得出结论，星云几乎光学厚度，并且必须具有非常低的尘埃含量，才能解释观测到的高Lyα当量宽度。对于我们采用的宇宙学和恒星形成参数，产生的恒星总质量似乎与相当小的星系的形成相对应，其中一些星系可能注定要合并。然而，如果我们假设恒星形成是连续的，初始质量函数的低质量截止值为0.1M☉，并且是一个平坦的加速宇宙，Ω0=0.2，ΩΛ=0.8，那么我们的一个源可能成为原巨型球状星系的重要候选者。在我们采样的共生体积中隐含的恒星形成密度可能比其他作者从Lyman Break星系测量得出的z~3处的恒星形成密度小一些，但量级相同。这一结果与Lyα发射体是高红移恒星形成区分布中的低金属度(或低尘埃)尾巴的预期一致。最后，在z~3处，Lyα发射体对H电离光子的贡献可能与类星体一样多。因此，它们对早期宇宙的电离预算具有潜在的重要意义。
Narrowband imaging surveys aimed at detecting the faint emission from the 5007 Å [O III] line of intracluster planetary nebulae in Virgo also probe high-redshift z ~ 3.1 Lyα emitters. Here we report on the spectroscopic identification of nine Lyα emitters at z = 3.13 with fluxes between 2 × 10-17 and 2 × 10-16 ergs cm-2 s-1 obtained with the FORS spectrograph at Unit 1 of the ESO Very Large Telescope (VLT UT1). The spectra of these high-redshift objects show a narrow, isolated Lyα emission with very faint (frequently undetected) continuum, indicating a large equivalent width. No other features are visible in our spectra. Our Lyα emitters are quite similar to those found by Hu, Cowie, and colleagues in 1998. For a flat universe with H0 = 70 km s-1 Mpc-1 and q0 = 0.5 (ΩΛ = 0), the Lyα luminosity of the brightest source is 1.7 × 109 L☉, and the comoving space density of the Lyα emitters in the searched volume is 5 × 10-3 Mpc-3. Using simple population synthesis models, on the assumption that these sources are regions of star formation, we conclude that the nebulae are nearly optically thick and must have a very low dust content in order to explain the high observed Lyα equivalent widths. For the cosmological and star formation parameters we adopted, the total stellar mass produced would seem to correspond to the formation of rather small galaxies, some of which are perhaps destined to merge. However, one of our sources might become a serious candidate for a protogiant spheroidal galaxy if we assumed continuous star formation, a low mass cutoff of 0.1 M☉ in the initial mass function (IMF), and a flat accelerating universe with Ω0 = 0.2 and ΩΛ = 0.8. The implied star formation density in our sampled comoving volume is probably somewhat smaller than, but of the same order of magnitude as, the star formation density at z ~ 3 derived by other authors from Lyman break galaxy surveys. This result agrees with the expectation that the Lyα emitters are a low-metallicity (or low-dust) tail in a distribution of star-forming regions at high redshifts. Finally, the Lyα emitters may contribute as many H-ionizing photons as QSOs at z ~ 3. They are therefore potentially significant for the ionization budget of the early universe.