AI 中文总结
该研究利用JWST NIRSpec MSA光谱，发现2≲z≲6的红矮点光学连续谱与宽线发射变异性弱于正常AGNs，其宽线变异性呈白噪声模式，与正常AGNs的红噪声模式存在显著差异。
AI 中文摘要
我们利用NEXUS项目的多历元JWST NIRSpec MSA光谱，对17个红矮点（Little Red Dots，LRDs）和14个蓝宽线活跃星系核（active galactic nuclei，AGNs）在2≲z≲6的红移范围内开展光谱测量，采样静止帧时标约为1-3个月。总体而言，与相似红移下的蓝JWST AGNs以及56个在Hα光度上匹配的低红移宽线AGNs相比，红矮点群体显示出显著增强的巴尔末减缩。红矮点的静止光学连续谱表现出极小的整体变异性（均方根≲3%），且总Hα发射的整体变异性也弱于在Hα光度和静止帧时标上匹配的低红移AGNs。基于流量不确定度，我们约束红矮点群体在这些时标内的本征Hα均方根变异性≲4%。将我们的结果与近年红矮点在年至十年时标上的宽线变异性测量结果相结合，揭示出跨所有时标的低水平白噪声模式，这与正常AGNs中观测到的变异性幅度（月时标上约6%）和红噪声模式形成鲜明对比。这些结果为日益增多的观测研究提供了补充，表明从群体层面看，红矮点在光学连续谱和宽线发射上均具有弱变异性。此外，独特的白噪声宽线变异性模式暗示，红矮点中的宽线发射产生机制与正常AGNs不同，且/或中心引擎驱动的电离流量具有不同特性。
英文摘要
We present spectral measurements for 17 Little Red Dots (LRDs) and 14 blue broad-line active galactic nuclei (AGNs) at $2\lesssim z \lesssim 6$ using multi-epoch JWST NIRSpec MSA spectra from the NEXUS program, sampling rest-frame timescales of $\sim 1-3$ months. Overall, the LRD population shows significantly enhanced Balmer decrement compared with both blue JWST AGNs at similar redshifts and 56 low-redshift broad-line AGNs matched in H$\rmα$ luminosity. The rest-optical continua of LRDs show little ensemble variability (rms $\lesssim 3\%$), and the total H$\rmα$ emission also shows weaker ensemble variability compared with low-redshift AGNs matched in H$\rmα$ luminosity and rest-frame timescales. Based on the flux uncertainties, we constrain the intrinsic H$\rmα$ rms variability to be $\lesssim 4\%$ for the LRD population over these timescales. Combining our results with recent broad-line variability measurements of LRDs over yearly to decade timescales reveals a low-level white-noise pattern across all timescales, in stark contrast to the variability amplitude ($\sim 6\%$ over monthly timescales) and red-noise pattern observed in normal AGNs. These results add to the growing observational studies that suggest population-wise, LRDs have weak variability both in optical continuum and broad-line emission. Furthermore, the distinct white-noise broad-line variability pattern suggests different production mechanisms of broad-line emission in LRDs as opposed to normal AGNs, and/or different properties of the driving ionizing flux from the central engine.
Comments24 pages, 10 figures, 2 tables. Submitted to ApJ. Key results are shown in Figures 8 & 9
