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首页> 外文期刊>The Astrophysical Journal. Letters >Stellar populations in the outer halo of the massive elliptical M49
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Stellar populations in the outer halo of the massive elliptical M49

机译：巨大椭圆M49外圈的恒星种群

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摘要

We use deep surface photometry of the giant elliptical M49 (NGC 4472), obtained as part of our survey for diffuse light in the Virgo Cluster, to study the stellar populations in its outer halo. Our data trace M49's stellar halo out to ～100 kpc (7r _e), where we find that the shallow color gradient seen in the inner regions becomes dramatically steeper. The outer regions of the galaxy are quite blue (B-V ～ 0.7); if this is purely a metallicity effect, it argues for extremely metal-poor stellar populations with [Fe/H] < -1. We also find that the extended accretion shells around M49 are distinctly redder than the galaxy's surrounding halo, suggesting that we are likely witnessing the buildup of both the stellar mass and metallicity in M49's outer halo due to late time accretion. While such growth of galaxy halos is predicted by models of hierarchical accretion, this growth is thought to be driven by more massive accretion events which have correspondingly higher mean metallicity than inferred for M49's halo. Thus the extremely metal-poor nature of M49's extended halo provides some tension against current models for elliptical galaxy formation.
机译：我们使用巨椭圆M49（NGC 4472）的深表面光度法作为处女座星团中漫射光的调查的一部分，来研究其外部光晕中的恒星种群。我们的数据追踪到M49的恒星晕光达到〜100 kpc（7r _e），在那里我们发现在内部区域看到的浅色渐变变得更加陡峭。银河系的外围很蓝（B-V〜0.7）;如果这纯粹是金属性效应，则表明[Fe / H] <-1的极贫金属恒星群体。我们还发现，M49周围扩展的吸积壳明显比银河系周围的晕圈红，这表明由于较晚的吸积，我们很可能目睹了M49外部晕圈中恒星质量和金属性的积累。虽然银河晕的这种增长是通过层次积聚模型预测的，但这种增长被认为是由更大规模的积聚事件驱动的，这些事件具有比M49的晕环推断的平均金属含量更高的平均金属度。因此，M49扩展的光环极度贫金属，这为目前椭圆形星系形成模型提供了一定的张力。

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