Near-infrared Emission Lines in Starburst Galaxies at 0.5 < z < 0.9: Discovery of a Merger Sequence of Extreme Obscurations-猫眼课题宝

DOI：

10.3847/2041-8213/aad33e

发表时间：

2018-07

期刊：

The Astrophysical Journal Letters

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

A. Calabró;E. Daddi;P. Cassata;M. Onodera;R. Gobat;A. Puglisi;S. Jin;Daizhong Liu;R. Amor'in;N. Arimoto;M. Boquien;R. Carraro;D. Elbaz;E. Ibar;S. Juneau;F. Mannucci;Hugo M'endez Hern'anez;E. Oliva;G. Rodighiero;F. Valentino;A. Zanella

我们获得了25个星暴星系的光学/近红外静止标架麦哲伦火光谱(包括Paβ和Paγ)，其平均恒星形成率(Sfr)是主序列(MS)的7倍。我们发现，在对应于AV∼2-3 MAG的恒定值附近，帕森-巴尔默线比饱和，而线-红外光度比表明存在更大范围的更极端的遮挡，并且似乎与前者无关。这一行为与为本地和遥远星系得出的标准衰减定律不一致，但与对年轻恒星和尘埃均匀混合的恒星爆发核心的观测结果非常一致。这个模型意味着星暴中心的AV=2-30毫克衰减，中位数为∼9毫克(4,000倍)。我们样品中六个活动星系核的X射线硬度比以及从观测到的尘埃质量和射电大小得出的柱密度独立地证实了这种衰减水平。在这种情况下，观测到的光学/近红外发射来自表面区域，而内部的星暴核心是不可见的。因此，我们将高的[N II]/Hα比率归因于来自吸积、湍流和动力扰动的广泛激波，而不是活动星系核。大范围的光学深度表明，恒星暴增群体中存在着相当大的多样性，可能与不同的合并阶段或前身属性有关。事实上，我们的大多数目标在形态上都被归类为合并。我们认为，这种极端的模糊本身就提供了合并起源的确凿证据，也是识别红移更高的合并的有力工具。

We obtained optical/near-IR rest-frame Magellan FIRE spectra (including Paβ and Paγ) of 25 starburst galaxies at 0.5 < z < 0.9, with average star formation rates (SFRs) seven times above the main sequence (MS). We find that Paschen-to-Balmer line ratios saturate around a constant value corresponding to AV ∼ 2–3 mag, while line-to-IR-luminosity ratios suggest a large range of more extreme obscurations and appear to be uncorrelated with the former. This behavior is not consistent with standard attenuation laws derived for local and distant galaxies, yet is remarkably consistent with observations of starburst cores in which young stars and dust are homogeneously mixed. This model implies AV = 2–30 mag attenuation to the center of starburst cores, with a median of ∼9 mag (a factor of 4000). X-ray hardness ratios for six AGNs in our sample and column densities derived from observed dust masses and radio sizes independently confirm this level of attenuation. In these conditions observed optical/near-IR emission comes from surface regions, while inner starburst cores are invisible. We thus attribute the high [N ii]/Hα ratios to widespread shocks from accretion, turbulence, and dynamic disturbances rather than to AGNs. The large range of optical depths demonstrates that substantial diversity is present within the starburst population, possibly connected to different merger phases or progenitor properties. The majority of our targets are, in fact, morphologically classified as mergers. We argue that the extreme obscuration provides in itself smoking gun evidence of their merger origin, and a powerful tool for identifying mergers at even higher redshifts.

Near-infrared Emission Lines in Starburst Galaxies at 0.5 < z < 0.9: Discovery of a Merger Sequence of Extreme Obscurations

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