标题： 长暴是否是恒星形成活动的有偏示踪？ 来自Swift/BAT6明亮长暴完整样本宿主星系的线索。 II：z < 1处的恒星形成率和金属丰度 显示英文标题

标题： Are LGRBs biased tracers of star formation? Clues from the host galaxies of the Swift/BAT6 complete sample of bright LGRBs. II: star formation rates and metallicities at z < 1

摘要： 长伽马射线暴（LGRBs）与大质量恒星的死亡有关，因此可能成为追踪宇宙恒星形成的一种强大工具。 然而，特别是在低红移（z < 1.5）时，LGRBs似乎更倾向于特定类型的环境。 我们的目标是研究一个完整样本的明亮LGRBs的宿主星系，以探讨环境对伽马射线暴形成的影响。 我们研究了Swift/BAT6完整样本中14个z < 1的明亮LGRBs的宿主星系光谱。 我们利用检测到的星际发射线来测量宿主的尘埃消光、恒星形成率（SFR）和星际金属量（Z），并将数据集补充了之前测量的恒星质量 M$_{\star}$。 获得的特性分布及其相互关系（例如，质量-金属量和SFR-M$_{\star}$关系）与场恒星形成星系的样本进行比较。我们发现，z < 1的LGRB宿主平均恒星形成率低于如果它们是直接恒星形成示踪剂的情况。 通过直接比较LGRB宿主和恒星形成星系的金属量分布，我们发现两者在Z $\sim 8.4-8.5$以内有很好的匹配，之后金属丰富的LGRB宿主数量不足的现象变得明显。 我们完整样本中的LGRB宿主星系与相似平均红移和恒星质量下的质量-金属量关系不矛盾。 对高金属量（和高质量）的限制可以解释LGRB宿主的低恒星形成率值。 我们发现，在Swift/BAT6 z < 1样本中，星暴星系的出现频率相对于场恒星形成群体有所增加。 鉴于平均恒星形成率较低，后者归因于较低的恒星质量。 然而，当前调查的完整性和金属量可用性的限制，加上LGRB宿主星系数量有限，使我们无法得出更定量的结论。 显示英文摘要

摘要： Long gamma-ray bursts (LGRBs) are associated with the deaths of massive stars and could thus be a potentially powerful tool to trace cosmic star formation. However, especially at low redshifts (z < 1.5) LGRBs seem to prefer particular types of environment. Our aim is to study the host galaxies of a complete sample of bright LGRBs to investigate the impact of the environment on GRB formation. We study host galaxy spectra of the Swift/BAT6 complete sample of 14 z < 1 bright LGRBs. We use the detected nebular emission lines to measure the dust extinction, star formation rate (SFR) and nebular metallicity (Z) of the hosts and supplement the data set with previously measured stellar masses M$_{\star}$. The distributions of the obtained properties and their interrelations (e.g. mass-metallicity and SFR-M$_{\star}$ relations) are compared to samples of field star-forming galaxies.We find that LGRB hosts at z < 1 have on average lower SFRs than if they were direct star-formation tracers. By directly comparing metallicity distributions of LGRB hosts and star-forming galaxies, we find a good match between the two populations up to Z $\sim 8.4-8.5$, after which the paucity of metal-rich LGRB hosts becomes apparent. The LGRB host galaxies of our complete sample are not inconsistent with the mass-metallicity relation at similar mean redshift and stellar masses. The cutoff against high metallicities (and high masses) can explain the low SFR values of LGRB hosts. We find a hint of increased incidence of starburst galaxies in the Swift/BAT6 z < 1 sample with respect to that of a field star-forming population. Given that the SFRs are low on average, the latter is ascribed to low stellar masses. Nevertheless the limits on the completeness and metallicity availability of current surveys, coupled with the limited number of LGRB host galaxies, prevent us from reaching more quantitative conclusions.