[论文解读] The ALMA Frontier Fields Survey III: 1.1 mm Emission Line Identifications in Abell 2744, MACSJ0416.1-2403, MACSJ1149.5+2223, Abell 370, and Abell S1063

Jorge González-López, F. E. Bauer+13 more|UCL Discovery (University College London)|Apr 10, 2017

Galaxies: Formation, Evolution, Phenomena参考文献 55被引用 7

一句话总结

本研究利用ALMA 1.1 mm连续谱观测，在五个前沿场星系团中识别出26个亚毫米波发射线候选体，结合深度近红外成像将这些线与星系关联。研究确认了九个高可靠性检测结果，包括红移0.28–3.07的CO跃迁，识别出两个星暴星系和一个受激波剥离影响的水母星系，证明了在具有辅助数据的广域连续谱巡天中进行意外发射线检测的可行性。

ABSTRACT

Most sub-mm emission line studies of galaxies to date have targeted sources with known redshifts where the frequencies of the lines are well constrained. Recent blind line scans circumvent the spectroscopic redshift requirement, which could represent a selection bias. Our aim is to detect emission lines present in continuum oriented observations. The detection of such lines provides spectroscopic redshift and yields properties of the galaxies. We perform a search for emission lines in the ALMA observations of five Frontier Fields clusters and assess the reliability of our detection by associating line candidates with detected galaxies in deep near-infrared imaging. We find 26 significant emission lines candidates, with observed line fluxes between 0.2-4.6 Jy km s$^{-1}$ and velocity dispersions (FWHM) of 25-600 km s$^{-1}$. Nine of these candidates lie nearby to near-infrared sources, boosting their reliability; in six cases the observed line frequency and strength are consistent with expectations given the photometric redshift and properties of the galaxy counterparts. We present redshift identifications, magnifications and molecular gas estimates for the galaxies with identified lines. We show that two of these candidates likely originate from starburst galaxies, one of which is a jellyfish galaxy, while another two are consistent with being main sequence galaxies based in their depletion times. This work highlights the degree to which serendipitous emission lines can be discovered in large mosaic continuum observations when deep ancillary data are available. The low number of high-significance line detections, however, confirms that such surveys are not as optimal as blind line scans. We stress that Monte Carlo simulations should be used to assess the line detections significances, since using the negative noise suffers from stochasticity and incurs larger uncertainties.

研究动机与目标

• 在五个大质量星系团的ALMA 1.1 mm连续谱观测中意外检测发射线。
• 通过在无先验红移信息的情况下识别线，克服发射线巡天中的选择偏差。
• 利用深度近红外成像将线候选体与星系关联，以提高检测可靠性。
• 估算已识别源的红移、放大因子和分子气体质量。
• 评估基于连续谱的线巡天与专用盲搜线扫描的有效性。

提出的方法

• 对Abell 2744、MACSJ0416.1-2403、MACSJ1149.5+2223、Abell 370和Abell S1063的ALMA 1.1 mm连续谱拼接图进行无偏置的发射线搜索。
• 使用负噪声和蒙特卡洛模拟评估检测显著性，因后者随机性较低而更受青睐。
• 通过哈勃空间望远镜近红外成像将线候选体与星系交叉识别，以评估空间重合度。
• 对线特征拟合高斯轮廓，以测量流量、速度宽度（FWHM）和红移。
• 将观测到的线频率和强度与基于光度红移预期的跃迁（如CO线）进行比较。
• 利用引力透镜模型校正放大效应，并推导源的本征物理性质。

实验结果

研究问题

• RQ1 在无先验红移信息的情况下，能否在ALMA连续谱观测中可靠检测发射线？
• RQ2 深度近红外成像在确认意外线候选体的天体物理起源方面有多有效？
• RQ3 检测到的源的红移、线识别及物理性质（如SFR、气体质量）是什么？
• RQ4 与专用盲搜线扫描相比，连续谱巡天的检测率和可靠性如何？
• RQ5 蒙特卡洛模拟在准确评估线显著性方面相较于负噪声起到什么作用？

主要发现

• 共检测到26个发射线候选体，观测到的线流量范围为0.2至4.6 Jy km⁻¹，FWHM速度弥散度在25至600 km s⁻¹之间。
• 九个线候选体与近红外星系在空间上接近，显著提高了其可靠性；其中六个候选体的线频率和强度与它们光度红移处预期的CO跃迁一致。
• 两个源被确认为星暴星系：一个正在经历激波剥离的水母星系，另一个是具有高SFR的明亮星暴星系。
• 另外两个源与主序列星系一致，其分子气体耗尽时标表明恒星形成效率适中。
• 本研究证实，蒙特卡洛模拟对于准确评估显著性至关重要，因为负噪声会导致更高的不确定性和随机性。
• 尽管意外检测取得成功，但高显著性检测数量稀少，证实连续谱巡天在大规模线巡天中不如专用盲搜线扫描最优。