Our neighboring galaxy M31 has been recently surveyed at the far- and near-ultraviolet (FUV and NUV) with the UVIT telescope on AstroSat, which provides unprecedented sensitivity to young stellar populations. Here the UVIT data are supplemented with optical data, near-infrared (IR) data (Spitzer), and mid- and far-IR data (Herschel). The observations are processed to obtain the spectral energy distributions (SEDs) for 73 regions covering M31. The SEDs are modeled using the Cigale SED fitting code with old and young stellar populations. The old stellar population has an age of 12 Gyr across M31 but has longer formation times at further distances from the center. Significant dependences on the position of dust extinction, dust emission, and young stellar population properties are found. Across M31, there are regions with a low-age (≲100 Myr) young population and regions with an intermediate-age (∼1 Gyr) young population. The mass in the young population has declined by a factor of ∼10 for ages 800–100 Myr ago but has increased again for ages ≲100 Myr. This indicates that cold gas available for star formation has been changing over the past Gyr, whether it is caused by a changing merger rate, changing gas infall, or changes in the gas reservoir in M31. We find that the dust luminosity, based on far-IR observations, is driven by the youngest stars, which are primarily measured in the FUV and NUV bands.

中文翻译：

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M31 恒星形成历史的远紫外到远红外光谱能量分布模型

最近，AstroSat 上的 UVIT 望远镜对我们邻近的星系 M31 进行了远紫外和近紫外（FUV 和 NUV）观测，这为年轻恒星群提供了前所未有的灵敏度。这里，UVIT 数据补充有光学数据、近红外 (IR) 数据 (Spitzer) 以及中红外和远红外数据 (Herschel)。对观测结果进行处理以获得覆盖 M31 的 73 个区域的光谱能量分布 (SED)。 SED 是使用 Cigale SED 拟合代码对老年和年轻恒星群体进行建模的。 M31 上的老恒星群的年龄为 12 吉里，但距离中心越远，形成时间就越长。发现了对尘埃灭绝位置、尘埃排放和年轻恒星种群特性的显着依赖。在 M31 上，存在低年龄（≲100 Myr）年轻人口的区域和中年龄（∼1 Gyr）年轻人口的区域。年龄在 800 至 100 密尔之前，年轻人口数量下降了约 10 倍，但在年龄 ≲100 密尔之前又再次增加。这表明可用于恒星形成的冷气体在过去的吉里一直在变化，无论是由合并率变化、气体流入变化还是M31气藏变化引起的。我们发现，基于远红外观测的尘埃光度是由最年轻的恒星驱动的，这些恒星主要在 FUV 和 NUV 波段进行测量。