星系II的分子和原子谱线巡天：恒星形成模式的无偏估计
Molecular and atomic line surveys of galaxies II: unbiased estimates of their star formation mode
摘要：
我们利用我们的“最小”冷星际介质（ISM）发射线模型，预测每单位致密的恒星形成气体质量的分子和原子线发射（Geach & Papadopoulos 2012;论文I），以检查在所谓的恒星形成“模式”的调查中关键线比率的效用，如xi_SF = M_dense（H_2）/M_total（H_2）所追踪的。我们认为，xi_SF和它的代理提供了非常敏感的，快速恒星爆发/合并驱动与长期静止/盘状恒星质量大会的歧视，与最有希望的诊断，在不久的将来被应用CO（4-3）/[CI]（1-0）。这些线几乎可以在0<z<2的整个范围内（因此覆盖了星系演化的大部分）使用阿塔卡马大型毫米波阵列进行访问。除了它们的诊断能力之外，这种组合的另一个优点是所观察到的谱线的频率（Δ nu_0 ~ 30 GHz）相似，导致对于固定孔径几乎空间匹配的光束，从而减轻了在解释星系平均谱线比率时分辨率/形态偏差的影响。最后讨论了利用SKA的高频分量进行深盲红移巡天发现具有很低xi_SF值的富H_2星系的能力。这些星系可能是在恒星形成开始之前看到的星暴星系的祖先;这样的星系可能是局部（气体表面密度）-（恒星形成速率）标度定律的一类极端异常值，这将把它们排除在当前的恒星形成或恒星质量选择样本之外。我们的保守模型表明，SKA可以检测到这样的系统驻留在z~3的速度为每小时20-200。
英文摘要：
We make use of our 'minimal' cold interstellar medium (ISM) emission line model that predicts the molecular and atomic line emission per unit dense, star-forming gas mass (Geach & Papadopoulos 2012; Paper I) to examine the utility of key line ratios in surveys of the so-called star formation 'mode' as traced by xi_SF = M_dense(H_2)/M_total(H_2). We argue that xi_SF and its proxies provide very sensitive, extinction-free discriminators of rapid starburst/merger-driven versus secular quiescent/disk-like stellar mass assembly, with the most promising diagnostic to be applied in the near-future being CO(4-3)/[CI](1-0). These lines are accessible across nearly the full range 0<z<2 (thus covering the bulk of galaxy evolution) with the Atacama Large Millimeter Array. In addition to their diagnostic power, another advantage of this combination is the similar observed frequencies (Delta nu_0 ~ 30 GHz) of the lines, resulting in nearly spatially-matched beams for a fixed aperture, thus mitigating the effects of resolution/morphology bias in the interpretation of galaxy-averaged line ratios. Finally we discuss the capability of deep blind redshift surveys with the high frequency component of the Square Kilometer Arrray (SKA) in discovering H_2-rich galaxies with very low xi_SF values. These could be the progenitors of starburst galaxies seen prior to the onset of star formation; such galaxies could be a class of extreme outliers from local (gas surface density)-(star formation rate) scaling laws, which would exclude them from current star formatation or stellar mass selected samples. Our conservative model suggests that SKA could detect such systems residing at z~3 at a rate of 20-200 per hour.
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