On the Origin of Star–Gas Counterrotation in Low-mass Galaxies
On the Origin of Star–Gas Counterrotation in Low-mass Galaxies
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DOI：
10.3847/1538-4357/ab2128
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发表时间：
2019-03
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影响因子：
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通讯作者：
T. Starkenburg;L. Sales;S. Genel;Christina M. Manzano-King;G. Canalizo;L. Hernquist
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文献类型：
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作者：
T. Starkenburg;L. Sales;S. Genel;Christina M. Manzano-King;G. Canalizo;L. Hernquist
星系中的恒星是由冷旋转支撑的气态盘形成的，这些气态盘位于暗物质晕的中心。在最简单的模型中，这种角动量是在晕塌陷时早期获得的，并在之后保留下来，这意味着恒星和气体成分的自旋是良好对齐的。然而，观测表明存在与恒星反向旋转的气态盘。我们使用 Illustris 数值模拟来研究低质量星系 (M⋆ = 2 × 109–5 × 1010 M⊙) 中这种反向旋转的起源，在这个样本中，合并并没有发挥重要作用。我们的样本中只有 ∼1% 在 z = 0 处显示出反向旋转的气态盘。这些反向旋转的气态盘出现在经历过重大气体去除事件的星系中，随后又获得了角动量未对准的新气体。在我们的模拟中，我们确定了导致气体损失的两个主要通道：强反馈爆发和飞越更大的群体环境期间的气体剥离。一旦稳定下来，反向旋转就会持续很长时间，我们的样本中的几个星系会持续显示超过 2 吉里的未对准成分。因此，除了对早期形态的轻微偏好以及在给定恒星质量下低于平均气体含量之外，与当今环境或结构特性可能不存在重大相关性。
Stars in galaxies form from the cold rotationally supported gaseous disks that settle at the center of dark matter halos. In the simplest models, such angular momentum is acquired early on at the time of collapse of the halo and preserved thereafter, implying a well-aligned spin for the stellar and gaseous component. Observations, however, have shown the presence of gaseous disks in counterrotation with the stars. We use the Illustris numerical simulations to study the origin of such counterrotation in low-mass galaxies (M⋆ = 2 × 109–5 × 1010 M⊙), a sample where mergers have not played a significant role. Only ∼1% of our sample shows a counterrotating gaseous disk at z = 0. These counterrotating disks arise in galaxies that have had a significant episode of gas removal followed by the acquisition of new gas with misaligned angular momentum. In our simulations, we identify two main channels responsible for the gas loss: a strong feedback burst and gas stripping during a flyby passage through a more massive group environment. Once settled, counterrotation can be long-lived with several galaxies in our sample displaying misaligned components consistently for more than 2 Gyr. As a result, no major correlation with the present-day environment or structural properties might remain, except for a slight preference for early-type morphologies and a lower than average gas content at a given stellar mass.