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arXiv 1502.07756astro-ph.GAastro-ph.COastro-ph.HE
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遥远X射线AGN的平均恒星形成率与AGN光度之间的一个非常平坦的关系

A remarkably flat relationship between the average star formation rate and AGN luminosity for distant X-ray AGN

F. Stanley, C. M. Harrison, D. M. Alexander, A. M. Swinbank, J. A. Aird, A. Del Moro, R. C. Hickox, J. R. Mullaney

摘要:

在这项研究中,我们研究了恒星形成率SFR和活动星系核光度L(活动星系核)之间的关系,对于~2000 X射线探测活动星系核。活动星系核的X射线光度跨越三个数量级(10^(42)< L(2- 8 keV)< 10^(45.5)erg/s),红移范围为z = 0.2 - 2.5。利用8 - 500 μ m的红外测光(包括Spitzer和Herschel的去混像),并考虑测光上限,我们将红外光谱能量分布分解为活动星系核和恒星形成成分。利用恒星形成时的红外光度,我们研究了平均SFR与红移和活动星系核光度的关系。与以前的研究一致,我们发现一个强大的平均SFR的红移的演变,跟踪观察到的整体恒星形成星系人口的演变。然而,我们发现,平均SFR和活动星系核的光度之间的关系是平坦的,在所有的红移和所有的活动星系核的光度调查相比,以前的研究,我们发现在广泛的活动星系核的光度调查的平均SFR之间的散射较少。通过比较经验模型,我们认为,所观察到的平坦的关系是由于短时间尺度的变化,在活动星系核的光度,驱动的质量吸积率的变化,洗出任何潜在的相关性SFR和L(活动星系核)。此外,我们表明,SFR和活动星系核光度(和它的归一化)之间的预测关系的确切形式是高度敏感的假设内在爱丁顿比分布。

英文摘要:

In this study we investigate the relationship between the star formation rate, SFR, and AGN luminosity, L(AGN), for ~2000 X-ray detected AGN. The AGN span over three orders of magnitude in X-ray luminosity (10^(42) < L(2-8keV) < 10^(45.5) erg/s) and are in the redshift range z = 0.2 - 2.5. Using infrared (IR) photometry (8 - 500um), including deblended Spitzer and Herschel images and taking into account photometric upper limits, we decompose the IR spectral energy distributions into AGN and star formation components. Using the IR luminosities due to star formation, we investigate the average SFRs as a function of redshift and AGN luminosity. In agreement with previous studies, we find a strong evolution of the average SFR with redshift, tracking the observed evolution of the overall star forming galaxy population. However, we find that the relationship between the average SFR and AGN luminosity is flat at all redshifts and across all the AGN luminosities investigated; in comparison to previous studies, we find less scatter amongst the average SFRs across the wide range of AGN luminosities investigated. By comparing to empirical models, we argue that the observed flat relationship is due to short timescale variations in AGN luminosity, driven by changes in the mass accretion rate, which wash out any underlying correlations between SFR and L(AGN). Furthermore, we show that the exact form of the predicted relationship between SFR and AGN luminosity (and it's normalisation) is highly sensitive to the assumed intrinsic Eddington ratio distribution.

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