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现今星系的不平衡性：与恒星形成、星系的化学演化和黑洞的生长的联系

The Lopsidedness of Present-Day Galaxies: Connections to the Formation of Stars, the Chemical Evolution of Galaxies, and the Growth of Black Holes

Timothy A. Reichard, Timothy M. Heckman, Gregory Rudnick, Jarle Brinchmann, Guinevere Kauffmann, Vivienne Wild

备注：
39 pages, 16 figures, 3 tables, accepted to ApJ. Updated author affiliations
发表信息：
Astrophys.J.691:1005-1020,2009
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摘要：

我们利用斯隆数字巡天（SDSS）对大约25，000个邻近星系（z < 0.06）样本中的不平衡性进行了调查。我们使用50%和90%光半径之间的m=1方位角傅立叶模式作为我们的不对称性度量。SDSS谱被用来测量恒星、气体和黑洞在最中心的几kpc尺度区域的性质。我们表明，有一个很强的联系在星系盘的外部和中心区域的恒星星族的年轻的不平衡。这种联系与星系的其他结构性质无关。这些结果提供了一个强大的吸积/相互作用/合并和由此产生的恒星形成之间的连接的统计特性。我们还表明，在星系的质量金属丰度关系的残差与不平衡（在固定的质量，更多的金属贫星系更不平衡）。这表明，导致不平衡和增强恒星形成的事件将金属丰度较低的气体输送到星系的中心区域。最后，我们发现，有一种趋势，更强大的活动星系核托管更不平衡的星系（在固定的星系质量，密度，或浓度）。然而，如果我们比较具有相同结构和中心恒星星族的样本，我们就会发现活动星系和非活动星系之间的不平衡性没有差异。这导致了下面的画面。在星系中心区域存在的冷气体（不管它的起源）对于恒星的形成和黑洞的生长都是必不可少的。冷气体的输送是由产生不平衡的过程辅助的。要将气体输送到黑洞，还需要其他一些过程，它们的尺度比我们的数据所能探测到的要小。

英文摘要：

We have used the Sloan Digital Sky Survey (SDSS) to undertake an investigation of lopsidedness in a sample of ~25,000 nearby galaxies (z < 0.06). We use the m=1 azimuthal Fourier mode between the 50% and 90% light radii as our measure of lopsidedness. The SDSS spectra are used to measure the properties of the stars, gas, and black hole in the central-most few-kpc-scale region. We show that there is a strong link between lopsidedness in the outer parts of the galactic disk and the youth of the stellar population in the central region. This link is independent of the other structural properties of the galaxy. These results provide a robust statistical characterization of the connections between accretion/interactions/mergers and the resulting star formation. We also show that residuals in the galaxy mass-metallicity relation correlate with lopsidedness (at fixed mass, the more metal-poor galaxies are more lopsided). This suggests that the events causing lopsidedness and enhanced star formation deliver lower metallicity gas into the galaxy's central region. Finally, we find that there is a trend for the more powerful active galactic nuclei to be hosted by more lopsided galaxies (at fixed galaxy mass, density, or concentration). However if we compare samples matched to have both the same structures and central stellar populations, we then find no difference in lopsidedness between active and non-active galaxies. This leads to the following picture. The presence of cold gas in the central region of a galaxy (irrespective of its origin) is essential for both star-formation and black hole growth. The delivery of cold gas is aided by the processes that produce lopsidedness. Other processes on scales smaller than we can probe with our data are required to transport the gas to the black hole.

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