The inhomogeneous ISM toward PKS 1830–211 SW: A detailed view of molecular gas at a look-back time of 7.5 Gyr
The inhomogeneous ISM toward PKS 1830–211 SW: A detailed view of molecular gas at a look-back time of 7.5 Gyr
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DOI：
10.1051/0004-6361/201425072
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发表时间：
2014-12
影响因子：
6.5
通讯作者：
A. Schulz;C. Henkel;K. Menten;S. Muller;D. Muders;J. Bagdonaite;W. Ubachs
中科院分区：
文献类型：
--
作者：
A. Schulz;C. Henkel;K. Menten;S. Muller;D. Muders;J. Bagdonaite;W. Ubachs
基于Effelsberg 100米望远镜的测量，对引力透镜系统PKS 1830-211的西南源进行了分子物种的多线研究，PKS 1830-211是迄今为止研究中间红移吸收分子气体的最著名的目标。确定谱线参数和光学深度，进行大速度梯度辐射传递计算，目的是：(1)评价z ~ 0.89处吸收前景气体的物理参数，特别是均匀性；(2)监测z ~ 2.5背景连续源波动引起的光谱时间变异性。我们发现，大多数分子种类的气体与n(H2) ~ 2 × 103 cm-3相当不均匀，但H2CO的值较高，SO的值较低。在2001 ~ 2012年十多年的时间间隔内测量CS J = 1←0跃迁，谱线的峰吸收深度基本保持不变，但谱线形状发生了显著变化。CS、HCO+和CH3OH数据在1996 - 2013年间显示了~2001年和2011/2012年的最大综合光深度。这与约10年的周期是一致的，然而，这需要通过长时间的监测来确认。将分子丰度与不同类型的银河系和邻近的河外云进行比较，我们发现观测到的云复体并不对应于一种特定的类型，而是对应于各种云类型，这些云类型具有更分散和更密集的成分，这可以预期为观察到的区域具有几个秒差距的横向线性尺度和沿着视线可能更大的深度。在18.343 GHz的c-C3H2 110−101谱线上，银河系吸收的初步探测也被报道。
Based on measurements with the Effelsberg 100-m telescope, a multiline study of molecular species is presented toward the southwestern source of the gravitational lens system PKS 1830–211, which is by far the best known target for studying molecular gas in absorption at intermediate redshift. Determining line parameters and optical depths and performing large velocity gradient radiative transfer calculations, the aims of this study are (1) to evaluate physical parameters of the absorbing foreground gas at z ~ 0.89, in particular its homogeneity; and (2) to monitor the spectroscopic time variability caused by fluctuations in the z ~ 2.5 background continuum source. We find, that the gas is quite inhomogeneous with n(H2) ~ 2 × 103 cm-3 for most molecular species but with higher values for H2CO and lower ones for SO. Measuring the CS J = 1 ← 0 transition during a time interval of more than a decade, from 2001 to 2012, the peak absorption depth of the line remains approximately constant, while the line shape undergoes notable variations. Covering the time between 1996 and 2013, CS, HCO+, and CH3OH data indicate maximum integrated optical depths in ~2001 and 2011/2012. This is compatible with a ~10 yr periodicity, which, however, needs confirmation by substantially longer time monitoring. Comparing molecular abundances with those of different types of Galactic and nearby extragalactic clouds we find that the observed cloud complex does not correspond to one particular type but to a variety of cloud types with more diffuse and denser components as can be expected for an observed region with a transverse linear scale of several parsec and a likely greater depth along the line of sight. A tentative detection of Galactic absorption in the c-C3H2 110−101 line at 18.343 GHz is also reported.