暗能量光谱仪中的氮强发射类星体。II. 宽线区金属丰度与相对氮增丰
Nitrogen-Loud Quasars from the Dark Energy Spectroscopic Instrument. II. Broad-Line Region Metallicity and Relative Nitrogen Enrichment
- National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）
- Technology and Engineering Center for Space Utilization, Chinese Academy of Sciences（中国科学院空间应用工程与技术中心）
- School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文学院）
- Key Laboratory for Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所粒子天体物理重点实验室）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究分析121个氮强发射类星体，发现其宽线区整体金属丰度较高且相对氮丰度增强，两者部分脱钩，为理解核环境异常丰度模式提供高金属丰度实验室。
AI中文摘要：
氮强发射（N-loud）类星体中异常强的氮发射究竟反映了整体高金属丰度、相对于其他元素的氮丰度增强，还是两者兼有，这一问题长期以来一直存在争议。我们分析了从暗能量光谱仪数据发布1中选出的121个红移范围为$2.13 \leq z \leq 3.90$的氮强发射类星体的宽线区（BLR）丰度，并构建了一个在红移、连续谱光度和维里黑洞质量上匹配的正常类星体对照样本。在氮强发射样本内，由N V/C IV推断的金属丰度范围约为$\sim 3$-$50\\,Z_\odot$，且系统性地高于由不依赖氮的（Si IV+O IV]）/C IV和Al III/C IV诊断所推断的值，后两者彼此高度一致，主要范围约为$\sim 1$-$20\\,Z_\odot$。与匹配的对照样本相比，氮强发射类星体在N V/C IV和（Si IV+O IV]）/C IV两种诊断中均表现出系统性更高的金属丰度，中值约为对照样本的三倍。值得注意的是，由N V/C IV和（Si IV+O IV]）/C IV推断的金属丰度之间的差异在氮强发射样本的高金属丰度端变得更加显著，这表明在整体金属增丰之外还存在额外的氮增丰。综合这些结果，氮强发射类星体既具有较高的整体BLR金属丰度，又具有增强的相对氮丰度，表明相对氮丰度至少部分地与整体金属丰度脱钩。因此，氮强发射类星体为理解核环境如何产生异常丰度模式提供了一个高金属丰度实验室，并为理解氮增丰如何随宇宙时间演化提供了补充视角。
英文摘要：
Whether the unusually strong nitrogen emission in nitrogen-loud (N-loud) quasars reflects high overall metallicity, enhanced nitrogen abundance relative to other elements, or both has long been debated. We analyze the broad-line region (BLR) abundances of 121 N-loud quasars at $2.13 \leq z \leq 3.90$ selected from the Dark Energy Spectroscopic Instrument Data Release 1 and construct a control sample of normal quasars matched in redshift, continuum luminosity, and virial black hole mass. Within the N-loud sample, metallicities inferred from N V/C IV span $\sim 3$-$50\,Z_\odot$ and are systematically higher than those inferred from the nitrogen-independent (Si IV+O IV])/C IV and Al III/C IV diagnostics, which agree closely and mainly span $\sim 1$-$20\,Z_\odot$. Compared with the matched controls, the N-loud quasars show systematically higher metallicities in both N V/C IV and (Si IV+O IV])/C IV, with median values approximately three times those of the controls. Notably, the discrepancy between the metallicities inferred from N V/C IV and (Si IV+O IV])/C IV becomes more pronounced toward the high-metallicity end of the N-loud sample, suggesting additional nitrogen enrichment beyond the overall metal enrichment. Together, these results indicate that N-loud quasars have both high overall BLR metallicity and enhanced relative nitrogen abundance, suggesting that relative nitrogen abundance is at least partially decoupled from overall metallicity. N-loud quasars therefore provide a high-metallicity laboratory for understanding how nuclear environments can produce unusual abundance patterns and offer a complementary view of how nitrogen enrichment arises across cosmic time.
