自z=1以来盘星系的显著尺寸演化：使用具有物理动机的尺寸指标重新探讨星系增长
Strong size evolution of disc galaxies since z = 1: Readdressing galaxy growth using a physically motivated size indicator
AI总结：
该研究以恒星形成气体密度阈值径向位置为新尺寸指标，基于HST CANDELS天区1048个盘星系数据，发现类银河系盘星系自z=1以来尺寸翻倍、外围剧烈演化，修正了以往用有效半径得出的平缓演化结论。
摘要：
我们对星系尺寸如何随宇宙时间演化的理解，建立在将半光（有效）半径用作尺寸指标的基础之上。尽管半光半径在对星系进行结构参数化方面有诸多优势，但它并不能衡量天体的整体延展范围，仅能指示包含星系最内部50%光度的区域的尺寸。因此，观测到的盘星系有效半径随宇宙时间的平缓演化，是由星系中心区域的演化而非整个结构的演化特性所决定的。\n在Trujillo等人（2020）和Chamba等人（2022）的工作基础上，我们将恒星形成的气体密度阈值的径向位置作为尺寸指标，研究盘星系的尺寸演化。我们用星系恒星面质量密度轮廓的截断（边缘）径向位置作为评估该物理量的代理指标。\n为开展这项研究，我们在HST CANDELS天区中筛选出1048个恒星质量M$_{\rm stellar}$ > 10$^{10}$ M$_{\odot}$、光谱红移最高达z=1的盘星系，推导了它们的面亮度、颜色和恒星质量密度轮廓。\n使用这种新的尺寸指标时，尺寸-质量关系的观测弥散（约0.1 dex）相比使用有效半径时降低了约2倍。在固定恒星质量下，类银河系（恒星质量M$_{\rm stellar}$ ~ 5$\times$10$^{10}$ M$_{\odot}$）的盘星系在过去80亿年间尺寸平均增长了1倍，而边缘位置的面恒星质量密度下降了一个多量级，从z=1时的约13 M$_{\odot}$/pc$^2$降至z=0时的约1 M$_{\odot}$/pc$^2$。这些结果反映了类银河系盘星系外围区域的剧烈演化，其增长速率约为1.5 kpc Gyr$^{-1}$。
英文摘要：
Our understanding of how the size of galaxies has evolved over cosmic time is based on the use of the half-light (effective) radius as a size indicator. Although the half-light radius has many advantages for structurally parameterising galaxies, it does not provide a measure of the global extent of the objects, but only an indication of the size of the region containing the innermost 50% of the galaxy's light. Therefore, the observed mild evolution of the effective radius of disc galaxies with cosmic time is conditioned by the evolution of the central part of the galaxies rather than by the evolutionary properties of the whole structure. Expanding on the works by Trujillo et al. (2020) and Chamba et al. (2022), we study the size evolution of disc galaxies using as a size indicator the radial location of the gas density threshold for star formation. As a proxy to evaluate this quantity, we use the radial position of the truncation (edge) in the stellar surface mass density profiles of galaxies. To conduct this task, we have selected 1048 disc galaxies with M$_{\rm stellar}$ $>$ 10$^{10}$ M$_{\odot}$ and spectroscopic redshifts up to z=1 within the HST CANDELS fields. We have derived their surface brightness, colour and stellar mass density profiles. Using the new size indicator, the observed scatter of the size-mass relation (~0.1 dex) decreases by a factor of ~2 compared to that using the effective radius. At a fixed stellar mass, Milky Way-like (M$_{\rm stellar}$ ~ 5$\times$10$^{10}$ M$_{\odot}$) disc galaxies have on average increased their sizes by a factor of two in the last 8 Gyr, while the surface stellar mass density at the edge position has decreased by more than an order of magnitude from ~13 M$_{\odot}$/pc$^2$ (z=1) to ~1 M$_{\odot}$/pc$^2$ (z=0). These results reflect a dramatic evolution of the outer part of MW-like disc galaxies, growing ~1.5 kpc Gyr$^{-1}$.
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