论文标题
分析星系尺寸与恒星质量关系
Analysis of the galaxy size versus stellar mass relation
论文作者
论文摘要
当使用固定表面密度时的大小而不是半质量半径RE时，星系尺寸与恒星质量（MSTAR）关系的散射大大减少。在这里，我们解决了为什么会发生这种情况。我们展示了如何预期的，因为具有相同MSTAR的任何两个星系具有至少一个半径，其表面密度相同，而星系的大小相同。然而，将散射降低到观察到的水平的原因并不小，我们将其固定在带有sersic曲线的星系表面密度曲线上，其RE和sersic Index（n）抗相关（即给定的mstar，n时，n降低时n增加）。我们的分析结果很好地描述了NASA Sloan Atlas（NSA）中所描绘的观察到的星系的行为，该星系包含7个<log（MSTAR/MSUN）<11.5的局部物体超过50万个局部对象。与NSA星系的比较还使我们能够找到质量表面密度（2.4m0.9p1.3 msun/pc2）和表面亮度（R波段24.7pm0.5 mag/arcsec2）的最佳值，以最大程度地减少散点，尽管实际值在某种程度上取决于用于优化NSA Galaxies的子集。存在最佳值的物理原因是未知的，但是，如Trujillo+20指出，它们接近气体表面密度阈值以形成恒星，因此可能会追踪星系的物理端。我们的基于NSA的大小 - 质量关系在斜坡上以及散布的大小上都一致。作为大小 - 质量关系的狭窄（仅0.06 dex）的副产品，我们建议使用星系的大小来测量其恒星质量。在观察时间方面，它的要求不如通常的光度法技术，并且在特定情况下可能会带来实际的优势。
The scatter in the galaxy size versus stellar mass (Mstar) relation gets largely reduced when, rather than the half-mass radius Re, the size at a fixed surface density is used. Here we address why this happens. We show how a reduction is to be expected because any two galaxies with the same Mstar have at least one radius with identical surface density, where the galaxies have identical size. However, the reason why the scatter is reduced to the observed level is not trivial, and we pin it down to the galaxy surface density profiles approximately following Sersic profiles with their Re and Sersic index (n) anti-correlated (i.e., given Mstar, n increases when Re decreases). Our analytical results describe very well the behavior of the observed galaxies as portrayed in the NASA Sloan Atlas (NSA), which contains more than half a million local objects with 7 < log(Mstar/Msun) < 11.5. The comparison with NSA galaxies also allows us to find the optimal values for the mass surface density (2.4m0.9p1.3 Msun/pc2) and surface brightness (r-band 24.7pm0.5 mag/arcsec2) that minimize the scatter, although the actual values depend somehow on the subset of NSA galaxies used for optimization. The physical reason for the existence of optimal values is unknown but, as Trujillo+20 point out, they are close to the gas surface density threshold to form stars and thus may trace the physical end of a galaxy. Our NSA-based size--mass relation agrees with theirs on the slope as well as on the magnitude of the scatter. As a by-product of the narrowness of the size--mass relation (only 0.06 dex), we propose to use the size of a galaxy to measure its stellar mass. In terms of observing time, it is not more demanding than the usual photometric techniques and may present practical advantages in particular cases.
