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arXiv 2107.05029astro-ph.GA
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SDSS-IV MaNGA中面向恒星形成星系外盘恒星星族的研究:H $α$缺乏的原因

A study of outer disk stellar populations of face-on star-forming galaxies in SDSS-IV MaNGA: causes of H$α$ deficiency

Guinevere Kauffmann

摘要:

对来自MaNGA巡天的正面成星星系的积分场单位(IFU)谱进行了径向叠加,使信噪比达到足以测量发射线和Lick指数的2.5- 3Re。三分之二的星系在外盘中有恒星星族,它们比内盘更老,更贫金属,尘埃更少。最近的恒星形成爆发在外盘发生得更频繁,但在D_n(4000)固定的情况下,这些区域中的Halpha等效宽度明显较低。我研究的属性的一个子集的星系最H $α$缺乏外磁盘。这些区域包含年轻的恒星星族,它们一定是在过去的0.5 Gyr内形成的,但经过消隐校正的Halpha值远低于标准Kroupa IMF的预测值。缺乏H α的星系具有平坦的D_n(4000)和H_delta_A轮廓,径向波动很小,表明恒星形成在整个盘上非常均匀地发生。H $α$谱线表明,电离气体的运动也是非常有规律的整个磁盘。关于H α缺乏的起源的主要线索是,它在尘埃消光突然减少的同一半径处开始,这表明在静止的、以HI为主的气体中,大质量恒星的恒星形成模式是缺乏的。最后,我已经进行了搜索的星系与签名不寻常的Halpha运动学,并发现15%的样品表现出显着的电离气体的证据,是从系统速度的磁盘位移。

英文摘要:

Integral field unit (IFU) spectra of face-on star-forming galaxies from the MaNGA survey are stacked in radial bins so as to reach a S/N high enough to measure emission lines and Lick indices out to 2.5-3 R_e. Two thirds of galaxies have stellar populations in the outer disks that are older, more metal poor and less dusty than in the inner disks. Recent bursts of star formation have occurred more frequently in the outer disk, but extinction-corrected Halpha equivalent widths are significantly lower at fixed D_n(4000) in these regions. I examine the properties of a subset of galaxies with the the most H$α$ deficient outer disks. These regions contain young stellar populations that must have formed within the last 0.5 Gyr, but extinction-corrected Halpha values well below the values predicted for a standard Kroupa IMF. The Halpha deficient galaxies have flat D_n(4000) and Hdelta_A profiles with little radial fluctuation, indicating that star formation has occurred extremely uniformly across the entire disk. The H$α$ line profiles indicate that the ionized gas kinematics is also very regular across the disk. The main clue to the origin of the Halpha deficiency is that it sets in at the same radius where the dust extinction abruptly decreases, suggesting a mode of star formation deficient in massive stars in quiescent, HI-dominated gas. Finally, I have carried out a search for galaxies with signatures of unusual Halpha kinematics and find that 15% of the sample exhibit evidence for significant ionized gas that is displaced from the systemic velocity of the disk.

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