AI 中文总结
本研究通过多历元NIRCam成像探测到“Capotauro”的自行，以>6σ置信度排除其为z≃32星系，证实其为距离730±110秒差距的Y型褐矮星，凸显多历元成像识别亚恒星污染物的价值。
AI 中文摘要
2025年在JWST深场成像中发现的致密红源“Capotauro”，因近红外相机（NIRCam）的极端颜色，曾被认为是红移z≃32的潜在星系候选体。但由于缺乏该源空间分辨的证据，与银河系恒星盘标高（≃500秒差距）相符的距离处，一颗极冷褐矮星为观测到的测光提供了另一种解释。本文利用发现数据后约3.5年获得的新中波段NIRCam成像来检验该假说。通过依赖滤光片的点扩散函数拟合、由68个致密参考源定义的稳健局域相对天体测量框架，以及联合四图像注入-恢复分析，我们显示Capotauro在3.5年的观测时间跨度内移动了132±20毫角秒，以>6σ的置信度排除了它是河外源（星系、活动星系核或超新星）的可能性。观测到的视自行（μ_ξ,μ_η）=(+9.4⁺⁶.⁴₋₄.₈, -35.6⁺⁵.¹₋₅.⁹)毫角秒/年，总自行为37.6⁺⁵.⁵₋⁵.⁶毫角秒/年。通过将其测光光谱能量分布与经验模板比较，我们发现Capotauro最符合光谱型Y1.0±0.5（有效温度T_eff≈350开尔文）、距离730±110秒差距的褐矮星（尽管现有数据和光谱模板不足以排除更冷、光谱型更晚的褐矮星）。因此，Capotauro是迄今发现的最远的Y型矮星之一，这与其在JWST深场河外巡天场中被发现的预期一致。该结果证明了多历元成像在识别最极端测光-红移候选体中的亚恒星污染物方面的价值。
英文摘要
The compact red source ``Capotauro'', discovered in deep JWST imaging in 2025, has been suggested as a possible galaxy candidate at redshift $z\simeq32$ on account of its extreme NIRCam colours. However, given the lack of evidence that this source is spatially resolved, a very cool brown dwarf, at a distance consistent with the scale-height of the Milky Way stellar disc ($\simeq 500$ pc), provides an alternative explanation of the observed photometry. Here we exploit new medium-band NIRCam imaging obtained $\simeq 3.5$ years after the discovery data to test this hypothesis. Using filter-dependent point-spread-function fitting, a robust local relative astrometric frame defined by 68 compact reference sources, and a joint four-image injection-recovery analysis, we show that Capotauro has moved by $132 \pm 20$ mas over the 3.5-yr interval span of the observations, ruling out the possibility that it is an extragalactic source (galaxy, AGN, or supernova) at $> 6 σ$. The observed apparent proper motion is $(μ_ξ,μ_η)=(+9.4^{+6.4}_{-4.8},-35.6^{+5.1}_{-5.9})$ mas yr$^{-1}$, or $37.6^{+5.5}_{-5.6}$ mas yr$^{-1}$ in total. Through comparison of its photometric spectral energy distribution with empirical templates, we find that Capotauro is best described as a brown dwarf of spectral type Y$1.0\pm0.5$ ($T_{\rm eff}\approx350$ K) at a distance of $730\pm110$ pc (although the existing data and spectral templates are insufficient to rule out an even colder, later-type brown dwarf). Capotauro is thus one of the most distant Y dwarfs found to date, as expected given its discovery in a deep JWST extragalactic survey field. This result demonstrates the value of multi-epoch imaging for identifying substellar contaminants among the most extreme photometric-redshift candidates.
Comments14 pages, 5 figures, 4 tables, submitted to MNRAS
