引力透镜B0218 +357中z=0.68处的甲醛反反转
Formaldehyde Anti-Inversion at z=0.68 in the Gravitational Lens B0218+357
摘要：
我们报道了在z=0.68466处对引力透镜系统B 0218 +357的吸收中邻甲醛（o-H2 CO）的110-111（6 cm）和211-212（2 cm）跃迁的新观测结果。辐射转移模型表明，这两个转换是反反转相对于4.6 K宇宙微波背景（CMB），无论源覆盖因子，与激发温度为~1 K和1.5-2 K的110-111和211-212线，分别。利用这些观测结果和假设梯度为1 km s^-1 pc^-1的大速度梯度辐射转移模型，我们得到了分子氢数密度为2 × 10^3 cm^-3 < n（H2）<1 × 10^4 cm^-3，柱密度为2.5 × 10^13 cm^-2 < N（o-H2 CO）<8.9 × 10^13 cm^-2，其中，允许的范围保守地包括两条线中可能的源覆盖因子的范围。测量结果表明，B 0218 +357透镜中的吸收云中的H2 CO激发与银河系分子云中的类似：如果没有背景类星体的照射，或者如果从另一个方向观察，它将显示H2 CO对CMB的吸收。
英文摘要：
We report new observations of the 110-111 (6 cm) and 211-212 (2 cm) transitions of ortho-formaldehyde (o-H2CO) in absorption at z=0.68466 toward the gravitational lens system B0218+357. Radiative transfer modeling indicates that both transitions are anti-inverted relative to the 4.6 K cosmic microwave background (CMB), regardless of the source covering factor, with excitation temperatures of ~1 K and 1.5-2 K for the 110-111 and 211-212 lines, respectively. Using these observations and a large velocity gradient radiative transfer model that assumes a gradient of 1 km s^-1 pc^-1, we obtain a molecular hydrogen number density of 2x10^3 cm^-3 < n(H2) < 1x10^4 cm^-3 and a column density of 2.5x10^13 cm^-2 < N(o-H2CO) < 8.9x10^13 cm^-2, where the allowed ranges conservatively include the range of possible source covering factors in both lines. The measurements suggest that H2CO excitation in the absorbing clouds in the B0218+357 lens is analogous to that in Galactic molecular clouds: it would show H2CO absorption against the CMB if it were not illuminated by the background quasar or if it were viewed from another direction.
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