标题： 分解半人马座A的核区环境：II. 广吸收线的性质 显示英文标题

标题： Disentangling the circumnuclear environs of Centaurus A: II. On the nature of the broad absorption line

摘要： 我们报告了在最近的强射电星系半人马座A（NGC 5128）核区观测到的原子气体（HI）和分子气体（通过CO(2-1)追踪）的红移吸收特征。 我们的HI观测使用甚长基线阵列允许我们以前所未有的亚秒差距分辨率分辨出内核0.3（或5.4 pc）范围内沿21厘米连续谱喷流不同位置的HI吸收轮廓。 此外，我们用亚毫米波阵列获得的CO(2-1)数据探测了大部分吸收性分子气体，而没有受到之前单天线CO观测中常见的发射污染影响。 这些数据揭示了视线方向上气体的物理性质，强调了关于产生宽吸收线（~55 km/s）气体性质的争议仍未解决。 首先，宽的HI线在中心和最亮的21厘米连续谱成分处比在距其约20毫角秒（或0.4 pc）远处的喷流区域更为显著。 这表明宽吸收线可能起源于靠近核区的气体，而非弥散且更远的气体。 其次，在CO(2-1)吸收光谱中检测到的不同速度组分与其它分子线（如HCO+(1-0)）的匹配情况良好，除了在HCO+(1-0)中检测到的宽吸收线（很可能与HI相关）。 由于活动星系核引起的分子氢解离似乎在距离<= 10 pc处效率较高，这可能有助于解释宽HI和分子线的深度。 显示英文摘要

摘要： We report on atomic gas (HI) and molecular gas (as traced by CO(2-1)) redshifted absorption features toward the nuclear regions of the closest powerful radio galaxy, Centaurus A (NGC 5128). Our HI observations using the Very Long Baseline Array allow us to discern with unprecedented sub-parsec resolution HI absorption profiles toward different positions along the 21 cm continuum jet emission in the inner 0."3 (or 5.4 pc). In addition, our CO(2-1) data obtained with the Submillimeter Array probe the bulk of the absorbing molecular gas with little contamination by emission, not possible with previous CO single-dish observations. We shed light with these data on the physical properties of the gas in the line of sight, emphasizing the still open debate about the nature of the gas that produces the broad absorption line (~55 km/s). First, the broad H I line is more prominent toward the central and brightest 21 cm continuum component than toward a region along the jet at a distance ~ 20 mas (or 0.4 pc) further from it. This suggests that the broad absorption line arises from gas located close to the nucleus, rather than from diffuse and more distant gas. Second, the different velocity components detected in the CO(2-1) absorption spectrum match well other molecular lines, such as those of HCO+(1-0), except the broad absorption line that is detected in HCO+(1-0) (and most likely related to that of the H I). Dissociation of molecular hydrogen due to the AGN seems to be efficient at distances <= 10 pc, which might contribute to the depth of the broad H I and molecular lines.