NGC 205中心的年轻恒星星族
The young stellar population at the center of NGC 205
摘要：
上下文NGC 205是一个奇特的矮椭圆星系，在它的中心有一群年轻的蓝色恒星。它们的起源仍有争议，中心的新恒星形成活动可能与NGC 205和M31之间的动力学相互作用有关。目标。研究了NGC 205中心核周围30 \arcsec（$\sim$ 120 pc）的恒星形成历史，以获得年轻恒星星族起源的线索.方法.深HST/ACS CCD测光的理论等时线和光度函数进行比较，以表征正在研究的区域的恒星含量和计算最近的SF率。结果我们的测光揭示了一个以前未被发现的年轻恒星的蓝色羽流，清晰可辨，直到I $\simeq$ 26。我们的分析表明，1.9 $\times10^5$ M $_\odot$产生于大约6200万年前到3.35亿年前的NGC 205内部区域，最近的一次小事件发生在2500万年前的$\sim$。这意味着在此期间恒星形成率为$\sim7\times10^{-4}$ M $_\odot$ /年。结论.观测到的年轻主序星的光度函数与恒星形成率恒定的模型的良好拟合，反对潮汐触发的恒星形成活动在过去的$\sim$ 3亿年。相反，恒定的SF可能与NGC 205与M 31的第一次相互作用相一致。
英文摘要：
Context. NGC 205 is a peculiar dwarf elliptical galaxy hosting in its center a population of young blue stars. Their origin is still matter of debate, the central fresh star formation activity possibly being related to dynamical interactions between NGC 205 and M31. Aims. The star formation history in the central 30\arcsec ($\sim$120 pc) around the NGC 205 central nucleus is investigated in order to obtain clues to the origin of the young stellar population. Methods. Deep HST/ACS CCD photometry is compared with theoretical isochrones and luminosity functions to characterize the stellar content of the region under study and compute the recent SF rate. Results. Our photometry reveals a previously undetected blue plume of young stars clearly distinguishable down to I$\simeq$26. Our analysis suggests that 1.9$\times10^5$ M$_\odot$ were produced between approximately 62 Myr and 335 Myr ago in the NGC 205 inner regions, with a latest minor episode occurring $\sim$25 Myr ago. This implies a star formation rate of $\sim7\times10^{-4}$ M$_\odot$/yr over this period. Conclusions. The excellent fit of the observed luminosity function of young main sequence stars obtained with a model having a constant star formation rate argues against a tidally triggered star formation activity over the last $\sim$300 Myr. Rather, a constant SF may be consistent with NGC 205 being on its first interaction with M 31.
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