河外巡天发现的三颗极冷褐矮星的JWST/NIRSpec光谱：磷化氢吸收的进一步证据
JWST/NIRSpec Spectra for Three Ultracool Brown Dwarfs Detected in Extragalactic Surveys: Further Evidence for Phosphine Absorption
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中文总结 AI 辅助
该研究分析了三颗河外巡天发现的极冷褐矮星的JWST/NIRSpec光谱，通过$\texttt{NIFTY}$模型拟合确定其类型、距离与金属丰度，发现JADES-GS-BD-11存在磷化氢吸收，支持磷化氢检测与金属丰度相关的理论。
中文摘要 AI 辅助
我们呈现了三颗在河外巡天数据中发现的极冷褐矮星的JWST NIRSpec棱镜光谱，其中两颗来自JWST高级深河外巡天（JADES），一颗来自作为Mirage或Miracle（MoM）项目一部分观测的河外研究公共发布成像（PRIMER）巡天。这些源的光谱表明，一颗为T6型矮星（JADES-GS-BD-11，有效温度T$_{\rm eff}$≈700K），两颗为Y0-Y1型矮星（JADES-GS-BD-5，T$_{\rm eff}$≈400K；MoM-239450，T$_{\rm eff}$≈500K）。使用$\texttt{NIFTY}$模型对光谱进行大气拟合与该分类一致，结果显示JADES-GS-BD-5距离太阳仅约150秒差距，MoM-239450距离太阳约700-800秒差距，JADES-GS-BD-11距离太阳约1千秒差距；后两颗较远源的最佳拟合为亚太阳金属丰度。JADES-GS-BD-5的观测光谱在J和H波段的发射远弱于Y型矮星大气模型，可能表明褐矮星中存在水冰云。JADES-GS-BD-11的光谱在4.3μm处有一个特征，与罕见的磷化氢分子吸收相符，置信度为2.6σ。鉴于该源的低金属丰度（[M/H]=-0.7），我们的发现支持褐矮星大气中检测磷化氢与大气金属丰度相关的理论。JWST/NIRSpec光谱学仍是理解这些遥远且极冷褐矮星性质的强大工具。
英文摘要
We present JWST NIRSpec prism spectra for three ultracool brown dwarfs discovered in extragalactic survey data, two from the JWST Advanced Deep Extragalactic Survey (JADES), and one from Public Release IMaging for Extragalactic Research (PRIMER) survey observed as part of the Mirage or Miracle (MoM) program. The spectra for these sources indicate that one is a T6 dwarf (JADES-GS-BD-11, T$_{\mathrm{eff}} = \sim 700$ K) and two are Y0-Y1 dwarfs (JADES-GS-BD-5, T$_{\mathrm{eff}} = \sim 400$ K, and MoM-239450, T$_{\mathrm{eff}} = \sim 500$ K). Model atmospheric fits with $\texttt{NIFTY}$ to the spectra are consistent with this classification, and indicate that JADES-GS-BD-5 is only $\sim 150$ pc from the Sun, MoM-239450 is $\sim 700 - 800$ pc from the Sun, and JADES-GS-BD-11 is $\sim 1$ kpc from the Sun, with these latter two more distant sources being best fit at sub-solar metallicities. JADES-GS-BD-5 has an observed spectrum with significantly weaker J and H band emission than Y dwarf atmospheric models, potentially indicating the presence of water ice clouds in the brown dwarf. The spectrum for JADES-GS-BD-11 has a feature at 4.3$μ$m consistent with absorption from the rarely seen phosphine molecule at $2.6σ$ confidence. Given the low metallicity for this source ([M/H] $ = -0.7$), our finding supports the theory that detecting phosphine in brown dwarf atmospheres is tied to atmospheric metallicity. JWST/NIRSpec spectroscopy continues to be a powerful tool for understanding the properties of these distant, and very cold brown dwarfs.
