论文标题
NGC 300是纯指数磁盘星系吗？
Is NGC 300 a pure exponential disk galaxy?
论文作者
论文摘要
NGC 300是雕塑家组的低质量磁盘星系。在文献中，它已被确定为纯指数磁盘星系，因为它的光度曲线可以很好地拟合在许多磁盘尺度长度上（I型）上的单个指数定律。我们使用$ hubble $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $，则比以前的任何其他研究都更深入。颜色幅度图显示了所有字段中大量的旧红色巨型分支（RGB）恒星，到$ r \ sim19 $ kpc（$ 32' $），以及内部地区的年轻人口。我们构建了年轻，中年和旧恒星种群的密度曲线。我们在旧的RGB和中级恒星的密度曲线上发现了两个明显的突破：一个$ r \ sim5.9 $ kpc的弯曲（II型），另一个$ \ sim8.3 $ kpc的上弯曲（III型）。此外，旧的RGB星星表现出负径向颜色梯度，其上弯曲为$ r \ sim8 $ 〜kpc，除此之外，恒星种群均匀陈旧（$> $ 7〜 gyr）和金属罚款（$ \ rm [fe/h] = -1.6^{+0.2} {+0.2} {+0.2} {+0.2} _ { - 0.4} $ { - { - { - { - { - { - { - { - { - { - 0.4}）。因此，就恒星密度和恒星种群而言，在$ r \ gtrapprox8 $ kpc处的外部恒星组件与内磁盘很好地分开。尽管我们对当前确定的NGC \，300是纯指数磁盘的智慧的智慧提出了怀疑，但应进行更详细的调查，以将郊区识别为磁盘或出色的光环。
NGC 300 is a low-mass disk galaxy in the Sculptor group. In the literature, it has been identified as a pure exponential disk galaxy, as its luminosity profile could be well fitted with a single exponential law over many disk scale lengths (Type I). We investigate the stellar luminosity distribution of NGC 300 using $Hubble$ $Space$ $Telescope$ (HST) archive data, reaching farther and deeper than any other previous studies. Color magnitude diagrams show a significant population of old red giant branch (RGB) stars in all fields out to $R\sim19$ kpc ($32'$), as well as younger populations in the inner regions. We construct the density profiles of the young, intermediate-aged, and old stellar populations. We find two clear breaks in the density profiles of the old RGB and intermediate-aged stars: one down-bending (Type II) at $R\sim5.9$ kpc, and another up-bending (Type III) at $R\sim8.3$ kpc. Moreover, the old RGB stars exhibit a negative radial color gradient with an up-bending at $R\sim8$~kpc, beyond which the stellar populations are uniformly old ($>$7~Gyr) and metal-poor ($\rm[Fe/H] = -1.6^{+0.2}_{-0.4}$ dex). The outer stellar component at $R\gtrapprox8$ kpc is, therefore, well separated from the inner disk in terms of the stellar density and stellar populations. While our results cast doubt on the currently established wisdom that NGC\,300 is a pure exponential disk galaxy, a more detailed survey should be carried out to identify the outskirts as either a disk or a stellar halo.
