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>Mapping Large-Scale Gaseous Outflows in Ultraluminous Galaxies with Keck?II ESI Spectra: Variations in Outflow Velocity with Galactic Mass*
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Mapping Large-Scale Gaseous Outflows in Ultraluminous Galaxies with Keck?II ESI Spectra: Variations in Outflow Velocity with Galactic Mass*
Measurements of interstellar Na I λλ5890, 5896 absorption lines in 18 ultraluminous infrared galaxies (ULIGs) have been combined with published Na I data, to reassess the dependence of galactic outflow speeds on starburst luminosity and galactic mass. The Doppler shifts reveal outflows of relatively cool gas in 15 of 18 ULIGs with an average outflow speed at the line center of 330 ± 100 km s-1. The relation between outflow speed and star formation rate (SFR), defined by the distribution's upper envelope over 4 orders of magnitude in SFR, demonstrates that winds from more luminous starbursts accelerate interstellar gas to higher speeds roughly as v ∝ SFR0.35. This result is surprising since, in the traditional model for starburst-driven winds, these relatively cool gas clouds are accelerated by the ram pressure of a hot, supernova-heated wind that exhibits weak (if any) X-ray temperature variation with increasing galactic mass. The lack of evidence for much hotter winds is partly a sensitivity issue, but the Na I velocities in ultraluminous starbursts actually are consistent with acceleration by the tepid wind, indicating that a hotter component is unlikely to dominate the momentum flux. The Na I velocities in the dwarf starburst winds do not reach the terminal velocity of a hot wind at the measured temperature of kT ~ 0.73 keV, a result that could be interpreted simply as evidence that the hot superbubbles are too confined in dwarf starbursts to generate a free-flowing wind. A dynamically motivated scenario, however, is that the dwarf starburst winds simply lack enough momentum to accelerate the clouds to the velocity of the hot wind. Among the subsample of starbursts with well-constrained dynamical masses, the terminal outflow velocities are always found to approach the galactic escape velocity. Motivated by a similar scaling relation for stellar winds, the galactic Eddington luminosity for dusty starbursts is shown to be within the range measured for ULIGs. If radiation pressure on dust grains, coupled to the cool wind, is indeed important for galactic wind dynamics, then feedback is stronger in massive galaxies than previously thought, helping shape the high-mass end of the galaxy luminosity function. Regardless of the nature of the acceleration mechanism in ULIGs, the mass flux of cool gas estimated from these data demonstrates that starburst-driven winds transport significant gas during the assembly stage of field elliptical galaxies, a factor that helps explain the rapid decline in SFR in these systems inferred from elemental abundance ratios.
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机译：已将18个超发光红外星系（ULIGs）中星际Na I λλ5890、5896吸收线的测量值与已发布的Na I数据相结合，以重新评估银河外流速度对爆炸形星光度和银河质量的依赖性。多普勒频移揭示出18个ULIG中有15个相对较冷的气体流出，线中心的平均流出速度为330±100 km s-1。流出速度与恒星形成率（SFR）之间的关系（由分布的上包络线在SFR中超过4个数量级定义）表明，来自更多发光星爆的风将星际气体加速到大约v ∝ SFR0.35的更高速度。这一结果令人惊讶，因为在星爆驱动风的传统模型中，这些相对凉爽的气体云被超新星加热的热风的冲压压力所加速，该风的X射线温度随银河的增加而变化不大（如果有）质量缺乏关于大风的证据在一定程度上是一个敏感性问题，但是超发光星爆中的Na I速度实际上与冷风的加速一致，这表明较热的分量不太可能主导动量通量。在实测温度kT〜0.73 keV时，矮星爆风中的Na I速度没有达到热风的终极速度，这一结果可以简单地解释为证据，表明热超泡太局限在矮星爆中而无法产生自由流动的风。但是，动态激发的场景是，矮星暴风根本没有足够的动量来将云加速为热风的速度。在动力质量受到严格限制的星爆子样本中，总是发现末端流出速度接近银河逃逸速度。受恒星风类似比例关系的激励，尘埃爆炸的银河爱丁顿光度显示在ULIG的测量范围内。如果与冷风耦合的尘埃颗粒的辐射压力确实对银河系风动力学至关重要，那么大型星系中的反馈比以前认为的要强，从而有助于塑造银河系光度函数的高质量端。无论ULIGs中加速机制的性质如何，根据这些数据估算的冷气质量通量表明，星爆驱动的风在场椭圆星系的组装阶段输送了大量的气体，这是一个解释SFR迅速下降的因素。这些系统是从元素丰度比推断出来的。
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