Title: FLARES IX: The Physical Mechanisms Driving Compact Galaxy Formation and Evolution Show Chinese title

Title: FLARES IX：驱动致密星系形成和演化的物理机制

Abstract: In the FLARES (First Light And Reionisation Epoch Simulations) suite of hydrodynamical simulations, we find the high redshift ($z>5$) intrinsic size-luminosity relation is, surprisingly, negatively sloped. However, after including the effects of dust attenuation we find a positively sloped UV observed size-luminosity relation in good agreement with other simulated and observational studies. In this work, we extend this analysis to probe the underlying physical mechanisms driving the formation and evolution of the compact galaxies driving the negative size-mass/size-luminosity relation. We find the majority of compact galaxies ($R_{1/2, \star}< 1 \mathrm{pkpc}$), which drive the negative slope of the size-mass relation, have transitioned from extended to compact sizes via efficient centralised cooling, resulting in high specific star formation rates in their cores. These compact stellar systems are enshrouded by non-star forming gas distributions as much as $100\times$ larger than their stellar counterparts. By comparing with galaxies from the EAGLE simulation suite, we find that these extended gas distributions `turn on' and begin to form stars between $z=5$ and $z=0$ leading to increasing sizes, and thus the evolution of the size-mass relation from a negative to a positive slope. This explicitly demonstrates the process of inside-out galaxy formation in which compact bulges form earlier than the surrounding discs. Show Chinese abstract

Abstract: 在FLARES（首次发光和再电离时代模拟）流体动力学模拟套件中，我们发现高红移（$z>5$）固有大小-光度关系出人意料地呈负斜率。 然而，在考虑尘埃消光效应后，我们发现UV观测大小-光度关系呈正斜率，与其它模拟和观测研究结果一致。 在本工作中，我们将这一分析扩展至探究驱动紧凑星系形成和演化的潜在物理机制，这些星系导致了负的大小-质量/大小-光度关系。 我们发现大多数紧凑星系（$R_{1/2, \star}< 1 \mathrm{pkpc}$），它们导致了大小-质量关系的负斜率，通过高效的中心冷却从扩展尺寸转变为紧凑尺寸，从而在其核心产生了高的单位恒星形成率。 这些紧凑恒星系统被非恒星形成气体分布包围，其范围可达它们恒星对应物的$100\times$倍。 通过与EAGLE模拟套件中的星系进行比较，我们发现这些扩展气体分布在$z=5$和$z=0$之间“开启”并开始形成恒星，导致尺寸增加，因此大小-质量关系从负斜率演变为正斜率。 这明确展示了由内而外的星系形成过程，其中紧凑的核球早于周围盘形成。