标题： 由赫歇尔- PACS 观测到的附近红外亮星系中的高 J CO 谱线阶跃分布 显示英文标题

标题： High-J CO SLEDs in nearby infrared bright galaxies observed by Herschel-PACS

摘要： 我们报告了附近活动星系核（AGN）和星暴星系以及若干合并系统和超亮红外星系（ULIRGs）的远红外（FIR）CO转动发射的探测结果。利用赫歇尔- PACS，我们在 J$_{upp}$ = 14 - 20 范围内（$\lambda \sim$ 130 - 185 $\mu$微米，$\nu \sim$ 1612 - 2300 GHz）检测到跃迁，并对 CO 线流量给出了上限（在两种情况下为探测值），最高可达 J$_{upp}$ = 30。这里获得的 PACS CO 数据为这一范围提供了首批充分采样的 FIR 星际 CO 转动能级分布图（SLEDs），并将成为未来高红移研究的重要参考。我们发现，即使在同类型星系之间，整体 SLED 形状也存在很大差异，这表明单纯依赖高 J CO 诊断来表征星系激发源存在不确定性。结合从文献中获取的低 J 线强度数据，我们绘制了 CO 比值图，并讨论了其在区分激发源和分子气体物理性质方面的潜在诊断价值。星系在该图中的位置与其激发机制的特征关系较小，而更倾向于指示温暖且密集的分子气体的存在（或不存在）。然后，我们使用大速度梯度（LVG）辐射转移模型定量分析了一组被检测源子集中 CO 发射的特性，以拟合 CO SLEDs。通过单组分和双组分 LVG 模型拟合气体的动能温度、速度梯度、数密度和柱密度，我们为每个相应源推导出分子气体质量和对应的 CO-to-H$_2$转换因子$\alpha_{CO}$。 对于ULIRGs，我们发现$\alpha$值在典型范围0.4-5 M$_\odot$/(K km s$^{-1}$pc$^2$)内，而对于其他天体， $\alpha$的变化范围在0.2到14之间。 最后，我们将我们的最佳拟合LVG模型进行比较。 显示英文摘要

摘要： We report the detection of far-infrared (FIR) CO rotational emission from nearby active galactic nuclei (AGN) and starburst galaxies, as well as several merging systems and Ultra-Luminous Infrared Galaxies (ULIRGs). Using Herschel-PACS, we have detected transitions in the J$_{upp}$ = 14 - 20 range ($\lambda \sim$ 130 - 185 $\mu$m, $\nu \sim$ 1612 - 2300 GHz) with upper limits on (and in two cases, detections of) CO line fluxes up to J$_{upp}$ = 30. The PACS CO data obtained here provide the first well-sampled FIR extragalactic CO SLEDs for this range, and will be an essential reference for future high redshift studies. We find a large range in the overall SLED shape, even amongst galaxies of similar type, demonstrating the uncertainties in relying solely on high-J CO diagnostics to characterize the excitation source of a galaxy. Combining our data with low-J line intensities taken from the literature, we present a CO ratio-ratio diagram and discuss its potential diagnostic value in distinguishing excitation sources and physical properties of the molecular gas. The position of a galaxy on such a diagram is less a signature of its excitation mechanism, than an indicator of the presence (or absence) of warm, dense molecular gas. We then quantitatively analyze the CO emission from a subset of the detected sources with Large Velocity Gradient (LVG) radiative transfer models to fit the CO SLEDs. Using both single-component and two-component LVG models to fit the kinetic temperature, velocity gradient, number density and column density of the gas, we derive the molecular gas mass and the corresponding CO-to-H$_2$ conversion factor, $\alpha_{CO}$, for each respective source. For the ULIRGs we find $\alpha$ values in the canonical range 0.4 - 5 M$_\odot$/(K kms$^{-1}$pc$^2$), while for the other objects, $\alpha$ varies between 0.2 and 14.} Finally, we compare our best-fit LVG model ..