Spatially resolved star formation relation in two HI-rich galaxies with central post-starburst signature
Spatially resolved star formation relation in two HI-rich galaxies with central post-starburst signature
复制标题
具有中央星暴后特征的两个富含 HI 的星系中空间分辨的恒星形成关系
DOI：
10.1051/0004-6361/201527922
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发表时间：
2016
影响因子：
6.5
通讯作者：
M. Owers
中科院分区：
文献类型：
--
作者：
A. Klitsch;M. Zwaan;H. Kuntschner;W. Couch;M. Pracy;M. Owers
语境。 E+A 星系是根据其光谱识别的星暴后系统。这些星系包含大量年轻的 A 型恒星成分，但没有显示出发射线，这表明只有很少的正在进行的恒星形成 (SF)。在大约一半的附近 E+A 星系中发现了 HI 21 厘米线发射，表明它们含有可以为活跃的 SF 提供燃料的气体库。目标。我们研究了两个富含 HI 的星系中原子和分子气体的分布和运动学，这些星系在中心显示出典型的 E+A 光谱，在较大半径处显示出 SF。根据我们的结果，我们的目标是推断这些星系的 SF 活动是否与盘状星系中看到的活动一致，或者它是否表明向另一个演化阶段的过渡。方法。我们展示了使用 Karl Jansky 甚大阵列 (VLA) 获得的 HI 21 cm 发射线和使用阿塔卡马大型毫米/亚毫米阵列 (ALMA) 获得的 CO(1-0) 发射线的高空间分辨率射电干涉观测结果。我们结合这些数据集，使用基于压力的 SF 关系来预测恒星形成率 (SFR)，并表明它与亚 kpc 尺度上的 H α 导出的 SFR 没有很好的相关性。我们应用最近开发的统计模型来研究 SF 关系的小规模行为，以预测和解释观察到的散射。结果。我们发现定期旋转的 HI 气体平稳地分布在整个圆盘上。两个星系中的任何一个都没有检测到 CO(1-0) 发射线。得出的 CO 质量上限意味着分子气体消耗时间 t(depl) 小于或类似于 20 Myr。然而，由于金属丰度较低，CO 到 H2 的转化因子高度不确定。在基于 H α 的恒星形成率和 HI 质量之间的关系中，我们观察到显着的分散性，我们证明了亚 kpc 尺度上独立 SF 区域的少量统计结果。结论。我们确认了 ESO534-G001 和 2dFRS S833Z022 的 HI 丰富度，并发现这些星系中原子 SF 关系的尺度依赖性与预测的小尺寸尺度散射增加一致。这是由于独立 HI 云和 SF 区域的采样不完整造成的。这一发现补充了现有文献，该文献报道了分子 SF 关系的尺度依赖性，表明原子相和分子相都容易受到各个区域的进化循环的影响。这表明原子气藏拥有大量的子结构，应该可以通过未来的高分辨率观测来观察到。
Context. E+A galaxies are post-starburst systems that are identified based on their optical spectra. These galaxies contain a substantial young A-type stellar component but display no emission lines, which indicates only little ongoing star formation (SF). HI 21 cm line emission is found in approximately half of the nearby E+A galaxies, indicating that they contain a reservoir of gas that could fuel active SF. Aims. We study the distribution and kinematics of atomic and molecular gas in two HI-rich galaxies, which show a typical E+A spectrum at the centre and SF at larger radii. From our results we aim to infer whether the SF activity of these galaxies is consistent with the activity seen in disc galaxies, or if it indicates a transition towards another evolutionary phase. Methods. We present newly obtained high spatial resolution radio interferometric observations of the HI 21 cm emission line using the Karl Jansky Very Large Array (VLA) and of the CO(1-0) emission line using the Atacama Large Millimeter/submillimeter Array (ALMA). We combine these data sets to predict the star formation rate (SFR) using a pressure-based SF relation and show that it does not correlate well with the SFR derived from H alpha on sub-kpc scales. We apply a recently developed statistical model for the small-scale behaviour of the SF relation to predict and interpret the observed scatter. Results. We find regularly rotating HI gas that is smoothly distributed across the entire disc. The CO(1-0) emission line is not detected for either of the two galaxies. The derived upper limit on the CO mass implies a molecular gas depletion time of t(depl) less than or similar to 20 Myr. However, because of the low metallicity, the CO-to-H2 conversion factor is highly uncertain. In the relations between the H alpha-based SFR and the HI mass, we observe a substantial scatter we demonstrate results from small-number statistics of independent SF regions on sub-kpc scales. Conclusions. We confirm the HI-richness of ESO534-G001 and 2dFRS S833Z022, and find that the scale dependence of the atomic SF relation in these galaxies is consistent with the predicted increase in the scatter towards small size scales. This is due to the incomplete sampling of independent HI clouds and SF regions. This finding adds to the existing literature, which has reported a scale dependence of the molecular SF relation, showing that the atomic and molecular phases are both susceptible to the evolutionary cycling of individual regions. This suggests that the atomic gas reservoirs host substantial substructure, which should be observable with future high-resolution observations.