Tracing the star formation history of cluster galaxies using the H$\alpha$/UV flux ratio
Tracing the star formation history of cluster galaxies using the H$\alpha$/UV flux ratio
复制标题
使用 H$alpha$/UV 通量比追踪星团星系的恒星形成历史
DOI：
10.1051/0004-6361:20034572
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发表时间：
2004
影响因子：
6.5
通讯作者：
A. Zaccardo
中科院分区：
文献类型：
--
作者：
J. Iglesias;A. Boselli;G. Gavazzi;A. Zaccardo
由于星系的Hα和UV通量分别对年龄<10 7和<10 8 yr的恒星群体敏感，它们的比值f（Hα）/f（UV）为我们研究t ≤ 10 8 yr的星系的近期星星形成历史提供了一个工具。观测到的f（Hα）/f（UV）比根据假设真实的延迟的、指数下降的星星形成历史的星群合成模型确定的预期值小2倍。我们讨论了可能影响观测到的f（Hα）/f（UV）比值的各种机制，并提出上述差异是由于星星形成区内的尘埃对莱曼连续谱光子的吸收，还是由于星星形成期的发生。根据演化准则将我们的样本分成不同的子样本后，我们发现我们的参考样本中未受星系团环境影响的星系的f（Hα）/f（UV）的平均值比预期值低两倍。我们认为，这种差异必须主要是由于星星形成区域内的莱曼连续谱光子的1045%的吸收。有明显迹象表明正在进行相互作用的星系显示出f（Hα）/f（UV）的平均值略高于参考值，正如预期的那样，如果这些物体的SFR增加了1/4。目前紫外线和Hα测光的准确性尚不足以清楚地阐明相互作用对f（Hα）/f（紫外线）比值的影响，但预计GALEX使命不久将带来显著的观测改进。
Since the Hα and UV fluxes from galaxies are sensitive to stellar populations of ages <10 7 and ≈10 8 yr respectively, their ratio f (Hα)/f (UV) provides us with a tool to study the recent t ≤ 10 8 yr star formation history of galaxies, an exercise that we present here applied to 98 galaxies in 4 nearby clusters (Virgo, Coma, Abell 1367 and Cancer). The observed f (Hα)/f (UV) ratio is ∼ a factor of two smaller than the expected one as determined from population synthesis models assuming a realistic delayed, exponentially declining star formation history. We discuss various mechanisms that may have affected the observed f (Hα)/f (UV) ratio and we propose that the above discrepancy arises from either the absorption of Lyman continuum photons by dust within the star formation regions or from the occurrence of star formation episodes. After splitting our sample into different subsamples according to evolutionary criteria we find that our reference sample of galaxies unaffected by the cluster environment show an average value of f (Hα)/f (UV) two times lower than the expected one. We argue that this difference must be mostly due to absorption of ≈45% of the Lyman continuum photons within star forming regions. Galaxies with clear signs of an ongoing interaction show average values of f (Hα)/f (UV) slightly higher than the reference value, as expected if those objects had SFR increased by a factor of � 4. The accuracy of the current UV and Hα photometry is not yet sufficient to clearly disentangle the effect of interactions on the f (Hα)/f (UV) ratio, but significant observational improvements are shortly expected to result from the GALEX mission.