João P V Benedetti, Rogério Riffel, Tiago Ricci, Rogemar A Riffel, Miriani Pastoriza, Marina Trevisan, Luis G Dahmer-Hahn, Daniel Ruschel-Dutra, Alberto Rodríguez-Ardila, Anna Ferré-Mateu, Alexandre Vazdekis, João Steiner
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For the first time, we measured the electron temperature in NGC 6868, finding values ranging from ∼14000 K in the central region to ≳ 20000 K with an outward increasing temperature gradient. The electron density map exhibits an inverse relationship, with central values reaching Ne ∼ 4000 cm-3 for the broad component decreasing to Ne ∼ 100 cm-3 towards the edges of the field of view. Using BPT diagrams, we found that all spaxels are consistent with both AGN and shock ionization. However, when this information is combined with our kinematic and temperature findings, and further supported by the WHAN diagram, we argue that an AGN is the dominant ionisation mechanism in the central region of NGC 6868, while the extended outer component is ionized by a combination of hot low-mass evolved stars and shocks. 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引用次数: 0
摘要
我们利用双子座/GMOS 积分场单元观测对 NGC 6868 星系内部区域(∼680 × 470 pc2)的电离气体进行了研究。通道图显示了复杂的运动学和形态学,表明在 NGC 6868 中有多个过程在起作用。通过发射线拟合,我们在数据中发现了两个无处不在的成分:一个窄成分(σ ∼ 110 km s-1)追踪电离气体盘,另一个宽成分(σ ∼ 300 km s-1)主要与流入/流出气体有关。得出的 V 波段红度的空间分布与恒星群合成的结果一致,但数值普遍较高。我们首次测量了NGC 6868的电子温度,发现其数值从中心区域的14000 K到20000 K不等,温度梯度向外递增。电子密度图显示出一种反比关系,宽分量的中心值达到 Ne ∼ 4000 cm-3,向视场边缘下降到 Ne ∼ 100 cm-3。利用 BPT 图,我们发现所有 Spaxels 都与 AGN 和冲击电离一致。然而,当这些信息与我们的运动学和温度研究结果相结合,并得到 WHAN 图的进一步支持时,我们认为在 NGC 6868 的中心区域,AGN 是主要的电离机制,而扩展的外围部分则是由热的低质量演化恒星和震荡共同电离的。根据我们的发现,冲击在这个星系的电离平衡中起着重要作用。
Digging deeper into NGC 6868 II: ionized gas and excitation mechanism
We studied the ionized gas in the inner region (∼680 × 470 pc2) of the galaxy NGC 6868 using Gemini/GMOS integral field unit observations. Channel maps reveal complex kinematics and morphology, indicating multiple processes at work in NGC 6868. Through emission-line fitting, we identified two ubiquitous components in our data: a narrow (σ ∼ 110 km s−1) tracing an ionized gas disc and a broad component (σ ∼ 300 km s−1) mainly associated with inflowing/outflowing gas. The derived V-band reddening shows a spatial distribution consistent with that obtained from stellar population synthesis, although with generally higher values. For the first time, we measured the electron temperature in NGC 6868, finding values ranging from ∼14000 K in the central region to ≳ 20000 K with an outward increasing temperature gradient. The electron density map exhibits an inverse relationship, with central values reaching Ne ∼ 4000 cm-3 for the broad component decreasing to Ne ∼ 100 cm-3 towards the edges of the field of view. Using BPT diagrams, we found that all spaxels are consistent with both AGN and shock ionization. However, when this information is combined with our kinematic and temperature findings, and further supported by the WHAN diagram, we argue that an AGN is the dominant ionisation mechanism in the central region of NGC 6868, while the extended outer component is ionized by a combination of hot low-mass evolved stars and shocks. According to our findings, shocks play a significant role in the ionization balance of this galaxy.
期刊介绍:
Monthly Notices of the Royal Astronomical Society is one of the world''s leading primary research journals in astronomy and astrophysics, as well as one of the longest established. It publishes the results of original research in positional and dynamical astronomy, astrophysics, radio astronomy, cosmology, space research and the design of astronomical instruments.