The rise and fall of the UV upturn: z = 0.3, 0.55, and 0.7
The rise and fall of the UV upturn: z = 0.3, 0.55, and 0.7
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UV 上升和下降：z = 0.3、0.55 和 0.7
DOI：
10.1093/mnras/sty1988
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发表时间：
2018
影响因子：
4.8
通讯作者：
Ali S
中科院分区：
文献类型：
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作者：
Ali S
本文分析了在四个星系团（atz= 0.3，0.55和0.7）中，亮度达到L * 点以下的红序星系中紫外线（UV）上升的强度。我们发现上升的发生率和强度在z = 0.55之前保持不变。相比之下，在z = 0.7的星系团中，紫外线上升的普遍性和强度显著减弱，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，并且在101 Gyr之后基本上完全发展。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子种群来产生上升的模型与这种行为最一致。恒星从红巨星分支开始演化的时期（z= 0.7）限制了它们的年龄和化学丰度。通过将我们的结果与YEPS氦增强的轨道模型的预测进行比较，我们发现，如果在zf = 0.4时形成，那么在0 <z< 0.55之间显示出一致的上升，但在z = 0.7时消失的太阳金属丰度子种群将需要氦丰度Y ≥ 0.45。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。
We have analysed the strength of the ultraviolet (UV) upturn in red sequence galaxies with luminosities reaching to below theL* point within four clusters atz= 0.3, 0.55, and 0.7. We find that the incidence and strength of the upturn remains constant up toz= 0.55. In comparison, the prevalence and strength of the UV upturn is significantly diminished in thez= 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 ∼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 sub-population 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 byz= 0.7 would require a Helium abundance ofY≥ 0.45, if formed atzf∼ 4. 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.