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arXiv 1902.01401astro-ph.GA
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AGN一路下滑?类活动星系核的谱线比在最低质量孤立静态半导体中很常见

AGN All the Way Down? AGN-like Line Ratios are Common In the Lowest-Mass Isolated Quiescent Galaxies

C. Dickey, M. Geha, A. Wetzel, K. El-Badry

摘要:

我们调查了已知存在于孤立环境中的最低质量静止星系($\mathrm{M^* = 10^{9.0-9.5} \ M_\odot}$ ;距离更大质量星系1.5 Mpc)。这个人口可能代表最低的恒星质量星系,其中内部反馈淬火星系范围内的恒星形成。我们目前的凯克/ESI长缝光谱的27个孤立的星系在这个制度:20个静止星系和7个恒星形成的星系。我们测量发射线强度作为半径的函数,并将星系的鲍德温菲利普斯Terlevich(BPT)图。值得注意的是,在我们的样本中,20个静止星系中有16个拥有类似活动星系核的中心线比。由于空间分辨率和信噪比较低,这些静止星系中只有5个被SDSS识别为类活动星系核。我们发现,在我们的样本中的许多静止的星系在整个非SF区域的BPT空间的空间扩展的发射。当只考虑中央1 $^{\prime\prime}$,我们确定了一个紧密的关系,从BPT恒星形成序列和宿主星系恒星年龄跟踪的$\mathrm{D_n4000}$,这样,较老的恒星年龄与较大的距离恒星形成的轨迹。我们的研究结果表明,硬电离辐射(活动星系核线比)的存在本质上是什么可能是最低质量的自猝灭星系的猝灭。

英文摘要:

We investigate the lowest-mass quiescent galaxies known to exist in isolated environments ($\mathrm{M^* = 10^{9.0-9.5} \ M_\odot}$; 1.5 Mpc from a more massive galaxy). This population may represent the lowest stellar mass galaxies in which internal feedback quenches galaxy-wide star formation. We present Keck/ESI long-slit spectroscopy for 27 isolated galaxies in this regime: 20 quiescent galaxies and 7 star-forming galaxies. We measure emission line strengths as a function of radius and place galaxies on the Baldwin Phillips Terlevich (BPT) diagram. Remarkably, 16 of 20 quiescent galaxies in our sample host central AGN-like line ratios. Only 5 of these quiescent galaxies were identified as AGN-like in SDSS due to lower spatial resolution and signal-to-noise. We find that many of the quiescent galaxies in our sample have spatially-extended emission across the non-SF regions of BPT-space. When considering only the central 1$^{\prime\prime}$, we identify a tight relationship between distance from the BPT star-forming sequence and host galaxy stellar age as traced by $\mathrm{D_n4000}$, such that older stellar ages are associated with larger distances from the star-forming locus. Our results suggest that the presence of hard ionizing radiation (AGN-like line ratios) is intrinsically tied to the quenching of what may be the lowest-mass self-quenched galaxies.

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