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arXiv 1007.1409astro-ph.CO
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引力透镜类星体UM 673 A,B光谱中新发现的DLA和相关的Ly-alpha发射

A newly discovered DLA and associated Ly-alpha emission in the spectra of the gravitationally lensed quasar UM 673A,B

Ryan Cooke, Max Pettini, Charles C. Steidel, Lindsay J. King, Gwen C. Rudie, Olivera Rakic

摘要:

引力透镜类星体对UM 673 A,B的较亮成员的视线与z = 1.62650的阻尼莱曼α系统(DLA)相交,由于其低红移,以前没有被识别。我们的高质量阶梯光谱的对,获得与HIRES的凯克一号望远镜,显示中性氢柱密度N(H I)下降了至少400倍之间的UM 673 A和B,这表明DLA的范围在这个方向上是远远小于2.7 kpc之间的两个视线在z = 1.62650。通过重新评估这一新的情况以及其他类星体对的已发表数据,我们得出结论,在这些红移的DLA的典型大小(半径)是R ~(5 +/- 3)kpc,比以前实现的小。与DLA相关的高度电离气体更广泛,因为我们发现两条视线之间的CIV吸收曲线只有很小的差异。与UM 673 B重合,我们探测到一条弱而窄的Ly-alpha发射线,我们将其归因于SFR >~ 0.2M_solar/yr的恒星形成活动。UM 673 A中的DLA是贫金属的,具有总体金属丰度Z_DLA ~ 1/30 Z_solar,并且具有非常低的内部速度色散。它在其详细的化学成分中表现出一些明显的特点,元素Ti,Ni和Zn相对于Fe不足2-3倍。[Zn/Fe]比低于任何其他DLA或星系晕恒星的测量值,大概反映了恒星核合成之前的异常富集。我们讨论了这些结果的性质的星系托管DLA的影响。

英文摘要:

The sightline to the brighter member of the gravitationally lensed quasar pair UM 673A,B intersects a damped Lyman-alpha system (DLA) at z = 1.62650 which, because of its low redshift, has not been recognised before. Our high quality echelle spectra of the pair, obtained with HIRES on the Keck I telescope, show a drop in neutral hydrogen column density N(H I) by a factor of at least 400 between UM 673A and B, indicating that the DLA's extent in this direction is much less than the 2.7 kpc separation between the two sightlines at z = 1.62650. By reassessing this new case together with published data on other quasar pairs, we conclude that the typical size (radius) of DLAs at these redshifts is R ~ (5 +/- 3) kpc, smaller than previously realised. Highly ionized gas associated with the DLA is more extended, as we find only small differences in the C IV absorption profiles between the two sightlines. Coincident with UM 673B, we detect a weak and narrow Ly-alpha emission line which we attribute to star formation activity at a rate SFR >~ 0.2 M_solar/yr. The DLA in UM 673A is metal-poor, with an overall metallicity Z_DLA ~ 1/30 Z_solar, and has a very low internal velocity dispersion. It exhibits some apparent peculiarities in its detailed chemical composition, with the elements Ti, Ni, and Zn being deficient relative to Fe by factors of 2-3. The [Zn/Fe] ratio is lower than those measured in any other DLA or Galactic halo star, presumably reflecting somewhat unusual previous enrichment by stellar nucleosynthesis. We discuss the implications of these results for the nature of the galaxy hosting the DLA.

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