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arXiv 1808.04792astro-ph.GAastro-ph.SR
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等温塌陷气的合成光谱特征及侵入剖面的解释

Synthetic Spectral Signatures from Isothermal Collapsing Gas and the Interpretation of Infall Profiles

Robert M. Loughnane, Enrique Vázquez-Semadeni, Raúl Naranjo-Romero

备注：
The velocities in the radiative transfer analysis for each snapshot of the simulated collapsing core are a factor of 1.732 (the square root of 3) smaller along each of the three dimensions. This error is currently being rectified
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摘要：

考虑到最近的数值结果表明星前核的坍塌是从外到内而不是从内到外发生的，我们重新审视了对致密坍塌核中蓝色过量分子线的解释。因此，我们创建合成分子线观测模拟塌陷，球对称，低初始振幅的密度波动，嵌入在一个统一的，全球引力不稳定的背景下，没有湍流分量。坍缩的地核形成了一个扁平的、类似于Bonnor-Ebert的密度分布，但具有由外向内的径向速度分布，其中最大的下沉速度在大半径处，在低密度气体中，有云到地核的吸积，并且没有流体静力学的外包层。使用光学厚HCO $^+$ J=1-0和3-2旋转线，我们认为几个“典型”的波束宽度，并使用一个简单的线拟合模型来推断下落速度从合成的配置文件类似的是在标准线建模。我们发现，由于实际径向塌陷轮廓的由外向内的性质，推断的下落速度是实际峰值下落速度的~ 25-30%，因为最大速度被它们发生的低密度气体降低。此外，与N $_2$ H $^+$ $J_{F_1F}=1_{01}-0_{12}$超精细线，我们调查的不对称参数，$δv\equiv(V_{thick}-V_{thin})/Δv_{thin}$，在崩溃过程中的变化，发现与观察值很好的协议。最后，HCO $^+$ J=3-2谱线表现出极端的$T_b$ / $T_r$ -比值，就像那些演化的核心一样，对于坍缩后期的较大光束。我们的研究结果表明，标准的动态下降再现几个观察到的功能，但低质量的核心下降速度一般被低估，通常被解释为亚音速，虽然实际速度是超音速，由于不正确地假设一个由内而外的下降径向速度分布与静态的外壳。

英文摘要：

We revisit the interpretation of blue-excess molecular lines from dense collapsing cores, considering recent numerical results that suggest prestellar core collapse occurs from the outside-in, and not inside-out. We thus create synthetic molecular-line observations of simulated collapsing, spherically-symmetric, density fluctuations of low initial amplitude, embedded in a uniform, globally gravitationally unstable background, without a turbulent component. The collapsing core develops a flattened, Bonnor-Ebert-like density profile, but with an outside-in radial velocity profile, where the peak infall speeds are at large radii, in lower density gas, with cloud-to-core accretion, and no hydrostatic outer envelope. Using optically thick HCO$^+$ J=1-0 and 3-2 rotational lines, we consider several "typical" beamwidths and use a simple line-fitting model to infer infall speeds from the synthetic profiles similarly to what is done in standard line modeling. We find that the inferred infall speeds are ~ 25-30% of the actual peak infall speed as the largest speeds are downweighted by the low density gas in which they occur, due to the outside-in nature of the actual radial collapse profile. Also, with the N$_2$H$^+$ $J_{F_1F}=1_{01}-0_{12}$ hyperfine line, we investigate the change in the asymmetry parameter, $δv\equiv(V_{thick}-V_{thin})/Δv_{thin}$, during the collapse, finding good agreement with observed values. Finally, the HCO$^+$ J=3-2 lines exhibit extreme $T_b$/$T_r$-ratios like those for evolved cores, for larger beams late in the collapse. Our results suggest that standard dynamical infall reproduces several observed features, but that low-mass core infall speeds are generally undervalued, often interpreted as being subsonic although the actual speeds are supersonic, due to incorrectly assuming an inside-out infall radial velocity profile with a static outer envelope.

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