We investigate the formation and properties of low surface brightness galaxies (LSBGs) with $M_{*} > 10^{9.5} \mathrm{M_{\odot}}$ in the EAGLE hydrodynamical cosmological simulation. Galaxy surface brightness depends on a combination of stellar mass surface density and mass-to-light ratio ($M/L$), such that low surface brightness is strongly correlated with both galaxy angular momentum (low surface density) and low specific star formation rate (high $M/L$). This drives most of the other observed correlations between surface brightness and galaxy properties, such as the fact that most LSBGs have low metallicity. We find that LSBGs are more isolated than high surface brightness galaxies (HSBGs), in agreement with observations, but that this trend is driven entirely by the fact that LSBGs are unlikely to be close-in satellites. The majority of LSBGs are consistent with a formation scenario in which the galaxies with the highest angular momentum are those that formed most of their stars recently from a gas reservoir co-rotating with a high-spin dark matter halo. However, the most extended LSBG disks in EAGLE, which are comparable in size to observed giant LSBGs, are built up via mergers. These galaxies are found to inhabit dark matter halos with a higher spin in their inner regions ($<0.1r_{200c}$), even when excluding the effects of baryonic physics by considering matching halos from a dark matter only simulation with identical initial conditions.

中文翻译：

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鹰模拟中的大量低表面亮度星系

我们在 EAGLE 流体动力学宇宙学模拟中研究了 $M_{*} > 10^{9.5} \mathrm{M_{\odot}}$ 的低表面亮度星系 (LSBGs) 的形成和性质。星系表面亮度取决于恒星质量表面密度和质光比（$M/L$）的组合，因此低表面亮度与星系角动量（低表面密度）和低比恒星形成密切相关率（高 $M/L$）。这推动了大多数其他观察到的表面亮度和星系特性之间的相关性，例如大多数 LSBG 具有低金属丰度的事实。我们发现 LSBGs 比高表面亮度星系 (HSBGs) 更孤立，这与观测结果一致，但这种趋势完全是由 LSBGs 不太可能是近距离卫星这一事实驱动的。大多数 LSBG 与形成场景一致，其中具有最高角动量的星系是最近从与高自旋暗物质晕共同旋转的气藏中形成大部分恒星的星系。然而，EAGLE 中最扩展的 LSBG 磁盘，其大小与观察到的巨型 LSBG 相当，是通过合并建立的。发现这些星系居住在其内部区域（$<0.1r_{200c}$）中具有更高自旋的暗物质晕，即使通过考虑来自具有相同初始条件的仅暗物质模拟的匹配晕来排除重子物理学的影响. 然而，EAGLE 中最扩展的 LSBG 磁盘，其大小与观察到的巨型 LSBG 相当，是通过合并建立的。发现这些星系居住在其内部区域（$<0.1r_{200c}$）中具有更高自旋的暗物质晕，即使通过考虑来自具有相同初始条件的仅暗物质模拟的匹配晕来排除重子物理学的影响. 然而，EAGLE 中最扩展的 LSBG 磁盘，其大小与观察到的巨型 LSBG 相当，是通过合并建立的。发现这些星系居住在其内部区域（$<0.1r_{200c}$）中具有更高自旋的暗物质晕，即使通过考虑来自具有相同初始条件的仅暗物质模拟的匹配晕来排除重子物理学的影响.