Spectroscopy of Luminous Infrared Galaxies at 2 Microns. III. Analysis for Galaxies with log (LIR/L☉) ≳ 11.2
Spectroscopy of Luminous Infrared Galaxies at 2 Microns. III. Analysis for Galaxies with log (LIR/L☉) ≳ 11.2
复制标题
2 微米发光红外星系的光谱 III. log (LIR/L☉) ≳ 11.2 的星系分析
DOI：
10.1086/303448
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
D. Sanders
中科院分区：
文献类型：
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作者：
J. Goldader;Robert D. Joseph;R. Doyon;D. Sanders
我们已经获得了光谱的K窗口的第一个大样本的发光星系从IRAS调查。本文对光度为11.2 μ log（LIR/L）~ 11.9的43个系统进行了主成分分析。光谱本身在Goldader等人的配套论文（论文II）中给出。Brγ光度与LIR成正比，其水平与恒星形成区相似。这有力地表明，星星的形成占了这些物体能量产生的大部分，这与以前的研究基本一致。Leitherer & Heckman的连续星星形成模型与100 μ m以下的上限质量截断值吻合得很好。这些模型适用于~107至109年的星爆年龄范围。瞬时星爆模型适合的数据，但意味着一个不切实际的短范围的年龄为整个样本。很难不得出结论，初始质量函数在小于~1 μ g的恒星中是不足的。探测到氢分子的强发射线。H2 v = 1-0 S（1）线的光度与LIR成正比;这种相关性延伸到超亮红外星系。星系中的H2辐射比Brγ辐射在空间上扩展得更广。在我们的光谱中可见的各种H2线的比率的测量值和上限表明，在2 μm处的发射中看到的H2与被冲击激发一致。然而，不能排除在足够高的密度下运行的其他机制，即H2能级通过碰撞被热化。基于能量的考虑，我们认为这些冲击是由于超新星遗迹膨胀到星际介质中造成的。解释H2谱线发射所需的II型超新星的频率与从星暴模型和无线电/远红外相关性推导出的频率一致。然而，仍然有一些星系不能符合这个模型。在发现它十年后，我们仍然无法对亮红外星系中强烈的H2发射做出普遍的解释。在我们的调查中没有发现以前未被识别的宽线活动核;它们要么很弱，要么不存在，要么在2 μm处的真实光学深度远高于传统消光测量所指示的。然而，有明显的差异，K-波段的属性，包含宽线活跃的核和那些不。这些差异似乎是由于来自活动核本身的强烈非恒星连续辐射的存在。加上Goldader等人（论文I）的log（LIR/L反射）为12的13个超亮星系，在这个计划中观察到的系统总数为56个。我们已经将这些超亮星系纳入分析的某些部分，以检查我们样本整个光度范围内的特性。
We have obtained spectra across the K window for the first large sample of luminous galaxies selected from the IRAS survey. This paper contains the principal analysis of the 43 systems in our sample with luminosities of 11.2 ≲ log (LIR/L☉) ≲ 11.9. The spectra themselves were presented in a companion paper by Goldader et al. (Paper II). The Brγ luminosities are proportional to LIR, at levels similar to those of star-forming regions. This strongly suggests that star formation accounts for the bulk of the energy production in these objects, in general agreement with previous studies. Good agreement is found for the continuous star formation models of Leitherer & Heckman with upper mass cutoffs well below 100 ℳ☉. The models accommodate a range in starburst ages of ~107 to 109 yr. Instantaneous starburst models fit the data but imply an unrealistically short range of ages for the entire sample. It is difficult to avoid concluding that the initial mass functions are deficient in stars of less than ~1 ℳ☉. Strong emission lines from molecular hydrogen are detected. The H2 v = 1-0 S(1) line luminosities are proportional to LIR; the correlation extends through the ultraluminous infrared galaxies. The H2 emission in the galaxies tends to be more spatially extended than the Brγ emission. Measured values and upper limits for the ratios of the various H2 lines visible in our spectra indicate that the H2 seen in emission at 2 μm is consistent with being shock excited. However, other mechanisms, operating at sufficiently high densities that the H2 energy levels are thermalized by collisions, cannot be excluded. Based on energy considerations, we suggest that the shocks are due to supernova remnants expanding into the interstellar medium. The frequency of Type II supernovae necessary to account for the H2 line emission agrees with frequencies deduced from the starburst models and the radio/far-infrared correlation. However, there remain a number of galaxies that cannot be made to fit this model. A decade after its discovery, a universal explanation of the strong H2 emission in luminous infrared galaxies continues to elude us. No previously unrecognized broad-line active nuclei were discovered in our survey; either they are weak or absent or the true optical depths at 2 μm are much higher than indicated by conventional extinction measures. However, there are clear differences between the K-band properties of galaxies that contain broad-line active nuclei and those that do not. The differences seem to be due to the presence of strong nonstellar continuum emission coming from the active nuclei themselves. With the addition of the 13 ultraluminous galaxies with log (LIR/L☉) ≳ 12 from Goldader et al. (Paper I), the number of systems observed in this program totals 56. We have incorporated these ultraluminous galaxies in some parts of the analysis to examine properties across the entire luminosity range of our sample.