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arXiv 1906.10085astro-ph.GA
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M81中心秒差距内的流入气体

Inflowing Gas in the Central Parsec of M81

Nick Devereux

摘要:

最近用哈勃太空望远镜(HST)上的空间望远镜成像光谱仪(STIS)对M81的Seyfert 1/Liner核进行的光谱观测显示,它具有丰富的紫外-可见光谱,其中有各种宽度、电离势和临界密度的发射线,包括以前没有报道过的几个紫外线。即使在HST目前可达到的最高角分辨率下,M81的宽线区域也不能根据常用的观测值(如发射线的半峰全宽或各种发射线的比率)唯一地定义。大量的宽禁带使光谱的解释复杂化。至少推断出三个单独的线发射分量。一个大的、高度电离的、低密度、低金属量的H ${^+}$区域,产生宽的巴耳末线。位于H ${^+}$区域内的是跨越宽范围密度的较小凝聚体,以及通过相应离子的碰撞激发的禁限线发射源。与H ${^+}$区和凝聚区交织在一起的是一个奇怪的时变CIV $λ$ 1548发射源。总的来说,这些意见可以定性地理解的背景下,一个大的H ${^+}$区域内的冲击激发射流腔的光致电离的中央UV-X射线源。H ${^+}$区域含有${\sim}$ 500 M ${\odot}$低金属丰度气体,对流入动态不稳定。以目前的速度,可用的H ${^+}$气体可以维持平流为主的吸积流,为中央紫外-X射线源提供10 $^{5}$年的动力。

英文摘要:

Spectroscopic observations of the Seyfert 1/Liner nucleus of M81, obtained recently with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST), have revealed a UV--visible spectrum rich with emission lines of a variety of widths, ionization potentials, and critical densities, including several in the UV that have not previously been reported. Even at the highest angular resolution currently achievable with HST, the broad-line region of M81 cannot be uniquely defined on the basis of commonly used observables such as the full-width at half maximum of the emission lines, or ratios of various emission lines. Numerous broad forbidden lines complicate interpretation of the spectra. At least three separate line-emitting components are inferred. A large, highly ionized, low density, low metallicity H${^+}$ region producing the broad Balmer lines. Located within the H${^+}$ region are smaller condensations spanning a wide-range in density, and the source of forbidden line emission through collisional excitation of the respective ions. Intermingled with the H${^+}$ region and the condensations is a curious extended source of time-variable CIV $λ$ 1548 emission. Collectively, these observations can be qualitatively understood in the context of a shock excited jet cavity within a large H${^+}$ region that is photoionized by the central UV--X-ray source. The H${^+}$ region contains ${\sim}$ 500 M${\odot}$ of low metallicity gas that is dynamically unstable to inflow. At the current rate, the available H${^+}$ gas can sustain the advection dominated accretion flow that powers the central UV--X-ray source for 10$^{5}$ years.

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