论文标题
超扩散星系是银河系大小吗？
Are ultra-diffuse galaxies Milky Way-sized?
论文作者
论文摘要
自引入以来已有近70年的历史，有效或半灯半径已成为表征星系尺寸的非常流行的选择。但是，有效半径可测量星系内的光的浓度，因此不会捕获与物体边缘或边界相关的大小的直观定义。因此，我们旨在证明使用有效的半径与矮人和银河系一样的星系相比，使用有效的半径得出关于微弱“超湿星系”（UDGS）的性质的不良后果。我们根据恒星形成所需的气体密度阈值的位置使用了一个量度，而不是有效的半径。与有效的半径相比，这种具有物理动机的定义使大小更接近星系的边界。因此，考虑到UDGS和常规矮人的尺寸和恒星质量密度曲线，我们发现UDG的大小在矮人的尺寸范围内。我们还表明，目前已知的UDG的尺寸与类似银河系的对象的尺寸相当。我们发现，平均而言，UDG的延长量是银河系的十倍。这些结果表明，对光浓度敏感的尺寸估计器的使用会导致误导性结果。
Now almost 70 years since its introduction, the effective or half-light radius has become a very popular choice for characterising galaxy size. However, the effective radius measures the concentration of light within galaxies and thus does not capture the intuitive definition of size which is related to the edge or boundary of objects. For this reason, we aim to demonstrate the undesirable consequence of using the effective radius to draw conclusions about the nature of faint 'ultra-diffuse galaxies' (UDGs) when compared to dwarfs and Milky Way-like galaxies. Instead of the effective radius, we use a measure of galaxy size based on the location of the gas density threshold required for star formation. Compared to the effective radius, this physically motivated definition places the sizes much closer to the boundary of a galaxy. Therefore, considering the sizes and stellar mass density profiles of UDGs and regular dwarfs, we find that the UDGs have sizes that are within the size range of dwarfs. We also show that currently known UDGs do not have sizes comparable to Milky Way-like objects. We find that, on average, UDGs are ten times smaller in extension than Milky Way-like galaxies. These results show that the use of size estimators sensitive to the concentration of light can lead to misleading results.
