通过JWST UNCOVER调查发现两颗晚T型棕矮星
Two late-T dwarfs at kiloparsec distances revealed by JWST UNCOVER survey
AI总结：
通过JWST UNCOVER调查发现两颗晚T型棕矮星，揭示其在银河系外缘的空间分布特征，表明近红外光度计对晚T型棕矮星具有高灵敏度，但需光谱学区分L型和高红移星系。
摘要：
我们对詹姆斯·韦伯太空望远镜的A2744深场区域进行了棕矮星候选者的搜索，以研究这些天体在千秒差距距离上的空间密度。我们的方法首先基于光度颜色进行初步筛选，随后通过光谱能量分布拟合来匹配恒星大气模型和高红移星系模板。这种方法得到了两个稳健的T型棕矮星候选者和一个可能的L亚矮星候选者。这两个T型棕矮星的估计银河高度分别为0.43和0.86千秒差距，可能分别位于银河薄盘和厚盘的外缘。我们在UNCOVER区域内测量到T型棕矮星的表面密度为每平方弧分0.094，低于之前的预测但与数量级一致。我们还提供了不同有效温度和光谱型bin中T5-T8.9矮星的空间密度估计，发现T5-T7型矮星在2千秒差距范围内的密度显著低于太阳邻域的对应值，而厚盘内的T8型矮星密度与本地值相当。我们的分析表明，宽波段近红外到中红外光度计对晚T型棕矮星具有高灵敏度，但对L型和早期T型棕矮星相对灵敏度较低。光谱学通常需要区分JWST深场中L型棕矮星、早期T型亚矮星和高红移星系的光度候选者。本研究展示了在前所未有的距离上扩展我们对棕矮星分布和特性理解的潜力，为太阳邻域以外的亚恒星体提供了新的见解。
英文摘要：
We conducted a search for brown dwarf candidates in a James Webb Space Telescope deep field around A2744 to investigate the space density of these objects at kiloparsec distances. Our methodology employed an initial selection based on photometric colours, followed by spectral energy distribution fitting to both stellar atmospheric models and high-redshift galaxy templates. This approach yielded two robust T dwarf candidates and one possible L subdwarf candidate. The T dwarfs have estimated Galactic heights of 0.43 and 0.86 kpc, likely residing near the outer edges of the Galactic thin and thick discs, respectively. We measure a T dwarf surface number density of 0.094 per squared arcmin in the UNCOVER field, lower than previous predictions but consistent at the order-of-magnitude level. We also provide space number density estimates for T5-T8.9 dwarfs across different effective temperature and spectral type bins, finding that T5-T7 dwarfs out to 2 kpc have significantly lower densities than their solar neighbourhood counterparts, whilst T8 dwarfs within the thick disc exhibit densities comparable to local values. Our analysis demonstrates that broad-band near- to mid-infrared photometry provides high sensitivity to late-T dwarfs but is relatively less sensitive to L and early-T dwarfs. Spectroscopy is typically required to distinguish photometric candidates of L dwarfs, early-T subdwarfs, and high-redshift galaxies in JWST deep fields. This study demonstrates the potential for expanding our understanding of brown dwarf distributions and characteristics at unprecedented distances, offering new insights into substellar populations beyond the solar neighbourhood.
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