Far Ultraviolet Spectroscopic Explorer and Space Telescope Imaging Spectrograph Observations of Intervening O VI Absorption Line Systems in the Spectrum of PG 0953+415
Far Ultraviolet Spectroscopic Explorer and Space Telescope Imaging Spectrograph Observations of Intervening O VI Absorption Line Systems in the Spectrum of PG 0953+415
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PG 0953 415 光谱中介入 O VI 吸收线系统的远紫外光谱探测器和空间望远镜成像摄谱仪观测
DOI：
10.1086/324288
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
P. Richter
中科院分区：
文献类型：
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作者：
B. Savage;K. Sembach;T. Tripp;P. Richter
利用远紫外光谱探测器（FUSE）和空间望远镜成像光谱仪（STIS）对明亮的类星体PG 0953+415（zem = 0.239）的星系际介质进行了观测。FUSE的光谱范围从905到1187纳秒，分辨率为25 km s-1，而STIS的光谱范围为1150-1730纳秒，分辨率为7 km s-1。在选定的波长范围内获得了30 km s-1的附加STIS观测。在H I Lyα、Lyβ、Lyγ、O VI λλ1031.93、1037.62、NV λλ1238.82、1242.80、C IV λλ1548.20、1550.77和C III λ977.02中检测到z = 0.06807的O VI系统。所观察到的柱密度可以模拟为一个低密度的干预气体的金属丰度的0.4倍太阳光电离与电离河外背景辐射的平衡。用电离参数log U =-1.35实现最佳拟合，这意味着nH ~ 10-5 cm-3和通过吸收气体的路径长度~80 kpc。在z = 0.14232的静止坐标系中，H I Lyα吸收的速度范围为410 km s-1，在0和80 km s-1附近最强。在该系统中，OVI λλ1031.93，1037.62的吸收在0 km s-1附近很强，在80 km s-1时没有检测到。C III λ977.02的吸收在80 km s-1时被检测到，但在0 km s-1时未被检测到。观测结果对z = 0.14232系统的性质进行了限制，但没有区分热气体中的碰撞电离与电离参数log U >-0.74的极低密度介质中的光电离。z = 0.06807和0.14232的O VI系统出现在红移处，在以PG 0953+415为中心的~1°视场中，WIYN对星系的红移测量确定的视线上，中间星系的数密度沿着出现峰值。我们结合联合收割机我们的观察PG 0953+415与其他类星体更新的估计低红移数密度的干预O VI系统。在总的无遮蔽红移路径Δz = 0.43上，我们探测到六个O VI系统，其O VI λ1031.93谱线的静止框架等效宽度超过50 mAh，当λ z = 0.09时，得到dN/dz = 14。这意味着重子对O-VI系统闭合密度的贡献有一个低的红移值，ΩB（O-VI）> 0.002 h，假设O-VI系统的平均金属丰度为0.1太阳能。
We present Far Ultraviolet Spectroscopic Explorer (FUSE) and Space Telescope Imaging Spectrograph (STIS) observations of the intergalactic medium toward the bright QSO PG 0953+415 (zem = 0.239). The FUSE spectra extend from 905 to 1187 Å and have a resolution of 25 km s-1, while the STIS spectra cover 1150-1730 Å and have a resolution of 7 km s-1. Additional STIS observations at 30 km s-1 are obtained in selected wavelength ranges. An O VI system at z = 0.06807 is detected in H I Lyα, Lyβ, Lyγ, O VI λλ1031.93, 1037.62, N V λλ1238.82, 1242.80, C IV λλ1548.20, 1550.77, and C III λ977.02. The observed column densities can be modeled as a low-density intervening gas with a metallicity of 0.4 times solar in photoionization equilibrium with the ionizing extragalactic background radiation. The best fit is achieved with an ionization parameter, log U = -1.35, which implies nH ~ 10-5 cm-3 and a path length of ~80 kpc through the absorbing gas. H I Lyα absorption at z = 0.14232 spans a velocity range of 410 km s-1 with the strongest components near 0 and 80 km s-1 in the z = 0.14232 rest frame. In this system, O VI λλ1031.93, 1037.62 absorption is strong near 0 km s-1 and not detected at 80 km s-1. C III λ977.02 absorption is marginally detected at 80 km s-1 but is not detected at 0 km s-1. The observations place constraints on the properties of the z = 0.14232 system but do not discriminate between collisional ionization in hot gas versus photoionization in a very low density medium with an ionization parameter log U > -0.74. The z = 0.06807 and 0.14232 O VI systems occur at redshifts where there are peaks in the number density of intervening galaxies along the line of sight determined from WIYN redshift measurements of galaxies in the ~1° field centered on PG 0953+415. We combine our observations of PG 0953+415 with those for other QSOs to update the estimate of the low-redshift number density of intervening O VI systems. Over a total unobscured redshift path of Δz = 0.43, we detect six O VI systems with rest-frame equivalent widths of the O VI λ1031.93 line exceeding 50 mÅ, yielding dN/dz = 14 for ⟨z⟩ = 0.09. This implies a low-redshift value of the baryonic contribution to the closure density of the O VI systems of Ωb(O VI) > 0.002 h, assuming that the average metallicity in the O VI systems is 0.1 solar.