活动星系核反馈对早型星系分子气藏的破坏
Destruction of Molecular Gas Reservoirs in Early-Type Galaxies by Active Galactic Nucleus Feedback
摘要：
为了解释我们今天看到的红色被动演化系统的人口，必须抑制早期星系及其祖先中晚期的残余恒星形成。同样，为恒星形成提供燃料的分子气体的残余或新吸积储层必须被破坏。这种早期星系中恒星形成的抑制现在通常归因于活动星系核的反馈，其中气体储存器在吸积到中心超大质量黑洞的阶段被加热并排出。然而，到目前为止，这种分子气体的破坏和活动星系核阶段之间联系的直接观测证据一直缺失。我们提出了新的毫米波长观测从IRAM 30米望远镜的一个样本的低红移SDSS早期型星系目前正在经历这一过程的淬火晚时间的恒星形成。我们的观测表明，分子气体的消失与黑洞吸积的开始在不到1亿年的时间内是一致的，而且消失的速度太快，不可能仅仅是恒星形成的结果。由于我们的样本星系没有与强大的类星体活动或射电喷流，我们得出结论，低光度AGN事件足以抑制残留的恒星形成的早期型星系。活动星系核反馈的这种“抑制模式”与星系形成早期阶段与强大类星体活动有关的“截断模式”非常不同。
英文摘要：
Residual star formation at late times in early-type galaxies and their progenitors must be suppressed in order to explain the population of red, passively evolving systems we see today. Likewise, residual or newly accreted reservoirs of molecular gas that are fuelling star formation must be destroyed. This suppression of star formation in early-type galaxies is now commonly attributed to AGN feedback wherein the reservoir of gas is heated and expelled during a phase of accretion onto the central supermassive black hole. However, direct observational evidence for a link between the destruction of this molecular gas and an AGN phase has been missing so far. We present new mm-wavelength observations from the IRAM 30m telescope of a sample of low redshift SDSS early-type galaxies currently undergoing this process of quenching of late-time star formation. Our observations show that the disappearance of the molecular gas coincides within less than 100 Myr with the onset of accretion onto the black hole and is too rapid to be due to star formation alone. Since our sample galaxies are not associated to powerful quasar activity or radio jets, we conclude that low-luminosity AGN episodes are sufficient to suppress residual star formation in early-type galaxies. This `suppression mode' of AGN feedback is very different from the `truncation mode' linked to powerful quasar activity during early phases of galaxy formation.
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