The stellar content of the isolated transition dwarf galaxy DDO210
The stellar content of the isolated transition dwarf galaxy DDO210
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DOI：
10.1111/j.1365-2966.2006.11053.x
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发表时间：
2006-09
影响因子：
4.8
通讯作者：
A. McConnachie;N. Arimoto;M. Irwin;E. Tolstoy
中科院分区：
文献类型：
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作者：
A. McConnachie;N. Arimoto;M. Irwin;E. Tolstoy
我们使用矮星系 DDO210 的 Subaru Suprime-Cam 和 VLT FORS1 光度测量来研究过渡型星系的整体恒星含量和结构特性（其特性介于矮不规则星系和矮椭球体系统之间）。这个星系足够孤立，潮汐相互作用不太可能以任何方式影响它的演化。 DDO210 的颜色星等图显示了红巨星分支 (RGB) 星群（带有 RGB 凸起）、明亮的渐近巨星分支星群、红色星团、年轻的主序星和蓝环星。最年轻的恒星在最近 60 Myr 内形成，与主星群相比具有明显的径向分布。虽然整体恒星空间分布和 H I 空间分布是同心的，但年轻恒星偏离 DDO210 的中心，并且与 H I 分布中的“凹痕”重合。形成年轻种群所需的隐含近期恒星形成率显着高于导出的当前恒星形成率，其系数> 10。DDO210中的大多数恒星被发现在红色团块中，其平均I带星等表明DDO210中大多数恒星的平均年龄为4(-1)(+2) Gyr。考虑到这个年龄，RGB 的颜色意味着 [Fe/H] 的平均金属丰度类似于或等于 -1.3。通过将红色团块的形状与各种恒星形成历史的模型进行比较，我们估计古老（> 10 Gyr）的恒星群最多可以贡献与 DDO210 中恒星的 20-30% 类似的贡献。 DDO210 不寻常的恒星形成历史、其低质量估计及其孤立的性质，让我们能够深入了解最低质量、未受干扰的矮星系晕中恒星形成的过程。
We use Subaru Suprime-Cam and VLT FORS1 photometry of the dwarf galaxy DDO210 to study the global stellar content and structural properties of a transition-type galaxy (with properties intermediate between dwarf irregular and dwarf spheroidal systems). This galaxy is sufficiently isolated that tidal interactions are not likely to have affected its evolution in any way. The colour-magnitude diagrams of DDO210 show a red giant branch (RGB) population (with an RGB bump), a bright asymptotic giant branch population, a red clump, young main-sequence stars and blue-loop stars. The youngest stars formed within the last 60 Myr and have a distinct radial distribution compared to the main population. Whereas the overall stellar spatial distribution and H I spatial distribution are concentric, the young stars are offset from the centre of DDO210 and are coincident with a 'dent' in the H I distribution. The implied recent star formation rate required to form the young population is significantly higher than the derived current star formation rate, by a factor of > 10. Most of the stars in DDO210 are found in a red clump, and its mean I-band magnitude suggests that the majority of stars in DDO210 have an average age of 4(-1)(+2) Gyr. Given this age, the colour of the RGB implies a mean metallicity of [Fe/H] similar or equal to -1.3. By comparing the shape of the red clump with models for a variety of star formation histories, we estimate that an old (> 10 Gyr) stellar population can contribute similar to 20-30 per cent of the stars in DDO210 at most. The unusual star formation history of DDO210, its low-mass estimate and its isolated nature, provide insight into how star formation proceeds in the lowest mass, unperturbed, dwarf galaxy haloes.