[论文解读] The CORALS Survey II: Clues to Galaxy Clustering Around QSOs from z_abs ~ z_em Damped Lyman Alpha Systems

Sara L. Ellison, Lin Yan+4 more|ArXiv.org|Dec 6, 2001

Galaxies: Formation, Evolution, Phenomena被引用 46

一句话总结

本研究利用近似光深的莱曼-α吸收体（PDLAs），其中吸收红移 ≈ 发射红移，作为高红移类星体周围星系团聚的示踪器。分析CORALS巡天中的射电选类星体，发现PDLAs的密度约为中间吸收体的4倍，表明射电噪类星体位于高密度、类似星系团的环境中。这支持了射电噪类星体倾向于在高红移时形成于富集星系团中的假设。

ABSTRACT

We present a list of z_abs ~ z_em (Delta v < 3000 km/s) DLAs discovered during the CORALS survey for absorbers in a radio-selected QSO sample. On the assumption that z_abs ~ z_em DLAs are neither ejecta from the QSO, nor part of the host galaxy itself, we use the number density statistics of these DLAs to investigate galaxy clustering near the QSO redshift. We find that n(z) of z_abs z_em DLAs in our radio-selected QSO sample is ~4 times larger than the number density of intervening DLAs, implying an excess of galaxies near the QSO. This result is further supported with the inclusion of the radio-loud QSOs in the FIRST survey, although the total number of DLAs is still small (4) and the result is currently only significant at approximately the 2 sigma level. Since all of the z_abs ~ z_em DLAs we identify in CORALS are found towards optically bright (B < 20) QSOs, there is no strong evidence (based on these limited statistics) that this population suffers from a severe dust bias. We compare our results with those from an optically-selected, radio-quiet QSO sample in order to determine whether there is evidence for an excess of galaxies around radio-loud versus radio-quiet QSOs. We find that the n(z) of z_abs ~ z_em DLAs towards radio-quiet QSOs is in agreement with the number density of intervening absorbers. This result, although currently limited by the small number statistics of our survey, supports the conclusion that radio-loud quasars are found preferentially in rich galaxy environments at high redshift. Finally, we report that one of the new z_abs ~ z_em DLAs discovered by CORALS has some residual flux in the base of the Lya trough which may be due to Lya emission, either from star formation in the DLA galaxy or from gas photoionised by the QSO.

研究动机与目标

• 研究近似光深的莱曼-α吸收体（PDLAs）是否可作为高红移类星体周围星系团聚的无偏示踪器。
• 评估射电噪类星体（RLQs）是否相比射电静类星体（RQQs）更倾向于位于密集星系环境中。
• 通过分析宿主PDLAs的类星体亮度，检验光学巡天中可能存在的尘埃消光偏差。
• 探索一个PDLA的莱曼-α吸收谷底残余流量的性质，可能指示恒星形成导致的莱曼-α发射或电离气体。

提出的方法

• 在CORALS巡天中识别满足 |z_abs - z_em| < 3000 km s⁻¹ 的PDLAs，表明其与类星体接近。
• 将射电选类星体方向的PDLAs红移分布（n(z)）与同一红移范围内中间DLAs的分布进行比较。
• 与FIRST巡天交叉比对，纳入更多射电噪类星体，并评估结果的一致性。
• 利用宿主PDLAs的类星体光学星等（B < 20）检验光学巡天中尘埃消光偏差的影响。
• 分析莱曼-α吸收谷底的残余流量，以搜寻莱曼-α发射的特征。

实验结果

研究问题

• RQ1 与中间DLAs相比，射电选类星体周围是否存在统计上显著的PDLAs过剩？
• RQ2 射电噪类星体在高红移时是否表现出比射电静类星体更高的星系过密度？
• RQ3 PDLA的探测是否因尘埃消光而对光学明亮类星体存在偏差？
• RQ4 PDLA中莱曼-α吸收谷底的残余流量是否可能指示恒星形成或电离气体导致的莱曼-α发射？

主要发现

• 射电选类星体方向的PDLAs数密度约为中间DLAs的4倍，表明这些类星体附近存在物质过密。
• 射电静类星体方向的PDLAs数密度与中间DLAs无明显差异，表明其环境无显著过密。
• CORALS样本中所有PDLAs均出现在光学明亮类星体（B < 20）方向，表明尘埃消光偏差对这些系统探测无显著影响。
• 在B0405−331方向的一个PDLA中，饱和莱曼-α吸收谷底检测到残余流量，可能源于恒星形成导致的莱曼-α发射或电离气体。
• 尽管受统计量限制，射电选类星体中PDLAs的过剩在约2σ水平显著，支持射电噪类星体在高红移时位于富集星系团中的假设。
• 结果与射电噪类星体倾向于在致密环境中形成的情境一致，可能与黑洞质量-星系核球质量关系有关。