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>Broad P V Absorption in the QSO PG 1254+047: Column Densities, Ionizations, and Metal Abundances in Broad Absorption Line Winds
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Broad P V Absorption in the QSO PG 1254+047: Column Densities, Ionizations, and Metal Abundances in Broad Absorption Line Winds
This paper discusses the detection of P V λλ1118, 1128 and other broad absorption lines (BALs) in archival Hubble Space Telescope spectra of the low-redshift BAL QSO PG 1254+047. The P V identification is secured by excellent redshift and profile coincidences with the other BALs, such as C IV λλ1548, 1550 and Si IV λλ1393, 1403, and by photoionization calculations showing that other lines near this wavelength, e.g., Fe III λ1123, should be much weaker than P V. The observed BAL strengths imply that either (1) there are extreme abundance ratios such as [C/H] +1.0, [Si/H] +1.8, and [P/C] +2.2, or (2) at least some of the lines are much more optically thick than they appear. I argue that the significant presence of P V absorption indicates severe line saturation, which is disguised in the observed (moderate-strength) BALs because the absorber does not fully cover the continuum source(s) along our line(s) of sight. The variety of observed BAL strengths and profiles results from a complex mixture of ionization, optical depth, and coverage fraction effects, making useful determinations of the abundance ratios impossible without a specific physical model. Computed optical depths for all UV resonance lines show that the observed BALs are consistent with solar abundances if (1) the ionization parameter is at least moderately high, log U -0.6, (2) the total hydrogen column density is log NH (cm-2) 22.0, and (3) the optical depths in strong lines like C IV and O VI λλ1032, 1038 are 25 and 80, respectively. These optical depths and column densities are at least an order of magnitude larger than expected from the residual intensities in the BAL troughs, but they are consistent with the large absorbing columns derived from X-ray observations of BAL QSOs. In particular, a nominal X-ray column density of log NH (cm-2) ~ 23 could produce the observed BAL spectrum if +0.4 log U +0.7 in a simple one-zone medium. The outflowing BAL region, at velocities from -15,000 to -27,000 km s-1 in PG 1254+047, is therefore a strong candidate for the X-ray absorber in BAL QSOs.
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机译：本文讨论了低红移BAL QSO PG 1254 + 047的档案哈勃太空望远镜光谱中P V λλ1118、1128和其他宽吸收线（BAL）的检测。通过与其他BAL（例如C IV λλ1548、1550和Si IV λλ1393、1403）的出色的红移和轮廓重合，以及通过光电离计算显示应确保接近此波长的其他线（例如Fe IIIλ1123），可以确保PV识别。比BV弱得多。观察到的BAL强度暗示（1）存在极高的丰度比，例如[C / H] +1.0，[Si / H] +1.8和[P / C] +2.2，或（ 2）至少某些线在光学上比看起来粗得多。我认为，P V吸收的显着存在表明线饱和严重，这在观察到的（中等强度）BAL中是伪装的，因为吸收剂并未完全覆盖我们视线的连续谱源。各种观察到的BAL强度和轮廓是由电离，光学深度和覆盖率效应的复杂混合产生的，因此，如果没有特定的物理模型，就不可能确定丰度比。计算出的所有紫外线共振线的光学深度表明，如果（1）电离参数至少中等偏高，log U -0.6，（2）总氢柱密度为log NH（cm-），则观察到的BAL与太阳丰度一致。 2）22.0和（3）像C IV和O VI λλ1032、1038这样的强线的光学深度分别为25和80。这些光学深度和柱密度比BAL槽中的剩余强度所预期的至少大一个数量级，但它们与从BAL QSO的X射线观察得出的大型吸收柱一致。特别是，如果在简单的一区介质中+0.4 log U +0.7，则标称X射线柱密度为log NH（cm-2）〜23可以产生观察到的BAL光谱。因此，PG 1254 + 047中速度为-15,000到-27,000 km s-1的BAL流出区域是BAL QSO中X射线吸收器的强烈候选对象。
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