Neutral Hydrogen (21 Centimeter) Absorption in Seyfert Galaxies: Evidence for Free-Free Absorption and Subkiloparsec Gaseous Disks
Neutral Hydrogen (21 Centimeter) Absorption in Seyfert Galaxies: Evidence for Free-Free Absorption and Subkiloparsec Gaseous Disks
复制标题
塞弗特星系中的中性氢（21 厘米）吸收：自由-自由吸收和亚千秒差距气态盘的证据
DOI：
10.1086/307853
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
E. Brinks
中科院分区：
文献类型：
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作者：
J. Gallimore;S. Baum;C. O’Dea;A. Pedlar;E. Brinks
活跃星系被认为是由从宿主星系中移出并流入中央吸积盘的中性气体提供燃料和遮蔽的。我们对 Seyfert 和星爆核中的 21 cm 吸收进行了 VLA 成像调查，以研究近核环境中的中性气体。除 NGC 4151 外，吸收气体追踪 100 个与外星系盘对齐的 pc 级旋转盘。相对于非活动螺旋中的核盘，这些盘似乎富含原子气体。我们没有发现中性氢快速流入或流出的有力证据，但我们对质量流入速率的限制与供给塞弗特核所需的限制是一致的。在此调查的星系中，中性氢吸收仅在 NGC 4151 中追踪秒差距尺度的气体。根据吸收线的运动学，圆盘对称轴似乎与射电射流轴而不是外星系轴对齐。最令人惊讶的结果是，我们没有检测到隐藏的 Seyfert 1 核 Mrk 3、Mrk 348 和 NGC 1068 的中央射电源的 21 cm 吸收。此外，通常观察到延伸射电射流结构的 21 cm 吸收，但似乎避开了 Seyfert 核中的中央紧凑射电源。为了解释这些结果，我们提出向核的 21 cm 吸收受到自由吸收、激发效应（即增强的自旋温度）或模糊气体中的快速运动的抑制。讽刺的是，这些效应的含义是模糊盘必须很小，通常不大于几十秒差距。
Active galaxies are thought to be both fueled and obscured by neutral gas removed from the host galaxy and funneled into a central accretion disk. We performed a VLA imaging survey of 21 cm absorption in Seyfert and starburst nuclei to study the neutral gas in the near-nuclear environment. With the exception of NGC 4151, the absorbing gas traces 100 pc-scale, rotating disks aligned with the outer galaxy disk. These disks appear to be rich in atomic gas relative to nuclear disks in nonactive spirals. We find no strong evidence for rapid infall or outflow of neutral hydrogen, but our limits on the mass infall rates are compatible with that required to feed a Seyfert nucleus. Among the galaxies surveyed here, neutral hydrogen absorption traces parsec-scale gas only in NGC 4151. Based on the kinematics of the absorption line, the disk symmetry axis appears to align with the radio jet axis rather than the outer galaxy axis. The most surprising result is that we detect no 21 cm absorption toward the central radio sources of the hidden Seyfert 1 nuclei Mrk 3, Mrk 348, and NGC 1068. Moreover, 21 cm absorption is commonly observed toward extended radio jet structure but appears to avoid central, compact radio sources in Seyfert nuclei. To explain these results, we propose that 21 cm absorption toward the nucleus is suppressed by either free-free absorption, excitation effects (i.e., enhanced spin temperature), or rapid motion in the obscuring gas. Ironically, the implications of these effects is that the obscuring disks must be small, typically not larger than a few tens of parsecs.