UV上升趋势的上升和下降：$z=0.3,\ 0.55$和$0.7$
The rise and fall of the UV upturn: $z=0.3,\ 0.55$ and $0.7$
摘要：
本文分析了在$z$ = 0.3，0.55和0.7的四个星系团中，亮度达到$L^*$点以下的红序星系的紫外上升强度。我们发现，上升的发生率和强度保持不变，直到$z=0.55$。相比之下，$z=0.7$星系团中紫外线上升的普遍性和强度明显减弱，这意味着在一个典型的红序星系中负责上升的恒星种群在这个红移处才刚刚发展，并且基本上是由$\sim 1$ Gyr完全发展的。在所有试图解释紫外线上升现象的主流模型中，那些通过在（热）水平分支上存在氦增强的恒星亚群而产生上升的模型与这种行为最一致。负责上升的恒星第一次从红巨星分支演化的时代（$z=0.7$）限制了它们的年龄和化学丰度。通过比较我们的结果与由YEPS氦增强的太阳能模型所作的预测，我们发现，太阳金属丰度的子人口，显示一个一致的上升之间的$0<z<0.55$，但随后由$z=0.7$褪色将需要一个$Y\geqslant0.45$的氦丰度，如果形成在$z_f\sim4$。后来形成的红移和/或更高的金属丰度将进一步增加氦的增强，从而在这些星系团中产生观察到的上升，反之亦然。
英文摘要：
We have analysed the strength of the UV upturn in red sequence galaxies with luminosities reaching to below the $L^*$ point within four clusters at $z$ = 0.3, 0.55 \& 0.7. We find that the incidence and strength of the upturn remains constant up to $z=0.55$. In comparison, the prevalence and strength of the UV upturn is significantly diminished in the $z=0.7$ cluster, implying that the stellar population responsible for the upturn in a typical red sequence galaxy is only just developing at this redshift and is essentially fully-developed by $\sim 1$ Gyr later. Of all the mainstream models that seek to explain the UV upturn phenomenon, it is those that generate the upturn through the presence of a Helium-enhanced stellar subpopulation on the (hot) horizontal branch that are most consistent with this behaviour. The epoch ($z=0.7$) where the stars responsible for the upturn first evolve from the red giant branch places constraints on their age and chemical abundances. By comparing our results with the prediction made by the YEPS Helium-enhanced spectrophotometic models, we find that a solar metallicity sub-population that displays a consistent upturn between $0<z<0.55$ but then fades by $z=0.7$ would require a Helium abundance of $Y\geqslant0.45$, if formed at $z_f\sim4$. Later formation redshifts and/or higher metallicity would further increase the Helium enhancement required to produce the observed upturn in these clusters and vice versa.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
