z=0.225附近明亮旋涡星系晕中的高电离等离子体
Highly Ionized Plasma in the Halo of a Luminous Spiral Galaxy Near z=0.225
摘要：
本文分析了类星体H1821+643的紫外HST/STIS和FUSE光谱中检测到的z= 0.22496和z=0.22638的多相O-VI吸收系统的物理条件。这两个吸收体都可能与一个~2L* Sbc-Sc星系的扩展晕有关，该星系位于距视线约116 kpc的投影距离处。在C II、C III、C IV、O III、O VI、Si II、Si III和H I中检测到z=0.22496的吸收剂，显著性> 3 σ。该吸收体中的低和中等离子与[Si/H]和[C/H]为-0.6 dex的光电离气体中的起源一致。相比之下，更广泛的O VI吸收可能产生在碰撞电离等离子体在非平衡条件下。z=0.22638的系统具有宽Lya（BLA）和C III吸收，从O VI偏移v = -53 km/s。BLA的H I和C III线宽意味着T = 1.1 × 10^5 K。对于非平衡冷却，我们得到BLA中的[C/H]为-1.5 dex，总氢柱N（H）= 3.2 x 10^{18} cm^-2。偏离BLA的O VI，没有检测到H I或C III，可能在T ~ 3 x 10^5 K时发生碰撞电离。从观测到的多相特性和与发光星系的接近性，我们提出z=0.22496的吸收体是高度电离的银河系HVC的河外模拟物，其中O VI是在温暖的HVC气相和星系的热日冕晕之间的界面层处的过渡温度等离子体（T ~ 10^5 K）中产生的。z=0.22638的OVI-BLA吸收体可能是在附近星系的热气晕中追踪一个冷却的冷凝碎片。
英文摘要：
We present analyses of the physical conditions in the z=0.22496 and z=0.22638 multi-phase O VI absorption systems detected in the ultraviolet HST/STIS and FUSE spectra of the quasar H1821+643. Both absorbers are likely associated with the extended halo of a ~2L* Sbc-Sc galaxy situated at a projected distance of ~116 kpc from the sight line. The z=0.22496 absorber is detected in C II, C III, C IV, O III, O VI, Si II, Si III and H I at > 3 sigma significance. The low and intermediate ions in this absorber are consistent with an origin in photoionized gas with [Si/H] and [C/H] of -0.6 dex. In contrast, the broader O VI absorption is likely produced in collisionally ionized plasma under nonequilibrium conditions. The z=0.22638 system has broad-Lya (BLA) and C III absorption offset by v = -53 km/s from O VI. The H I and C III line widths for the BLA imply T = 1.1 x 10^5 K. For non-equilibrium cooling we obtain [C/H] of -1.5 dex and a total hydrogen column of N(H) = 3.2 x 10^{18} cm^-2 in the BLA. The O VI, offset from the BLA with no detected H I or C III, is likely collisionally ionized at T ~ 3 x 10^5 K. From the observed multiphase properties and the proximity to a luminous galaxy, we propose that the z=0.22496 absorber is an extragalactic analog of a highly ionized Galactic HVC, in which the O VI is produced in transition temperature plasma (T ~ 10^5 K) at the interface layers between the warm HVC gas phase and the hot coronal halo of the galaxy. The z=0.22638 O VI - BLA absorber could be tracing a cooling condensing fragment in the nearby galaxy's hot gaseous halo.
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