高红移红外发光星系中恒星形成和AGN之间的能量平衡
Balancing the Energy Budget between Star-Formation and AGN in High Redshift Infrared Luminous Galaxies
摘要：
我们提供了位于GOODS-N的22个星系的深斯皮策中红外光谱，以及16，24，70和850 μ m测光。该样品的红移范围为0.6 < z < 2.6，24 μ m的通量密度在~0.2-1.2 mJy之间，由SMG、活动星系核和光学微弱（z_AB > 25）源组成。我们发现，通过拟合本地SED与24 μ m测光单独获得的红外光度与那些额外的中红外光谱和更长波长的光度数据时，被用于具有z < 1.4 and 24um-derived IR luminosities typically >3 × 10^12 L_sun的星系匹配良好。然而，对于红移范围在1.4 < z < 2.6之间的星系，通常具有24 μ m导出的红外光度> 3 × 10^12 L_sun，当SED单独与24 μ m测光拟合时，红外光度被高估了约5倍。这一结果的出现部分是由于这样一个事实，即高红移星系表现出PAH EQW是大的本地星系相比，类似的光度。使用改进的估计，这些来源的红外光度，我们调查是否发现他们的红外辐射是过量的，相对于预期的基础上消光校正的紫外SFR，可能表明存在一个模糊的活动星系核。通过光谱分解的IRS光谱数据，我们能够隔离的部分红外光度所产生的活动星系核，而不是恒星形成活动。平均而言，这一部分仅占整个样品中总红外光度的约30%。被确定为具有中红外线过剩的来源中，一半是占使用适当的热辐射校正，而一半显示存在模糊AGN。我们没有发现在这个红移范围内的FIR无线电相关性的演变的证据，虽然SMG的IR/无线电比，平均而言，~3倍低于标称值。
英文摘要：
(abridged) We present deep Spitzer mid-infrared spectroscopy, along with 16, 24, 70, and 850um photometry, for 22 galaxies located in GOODS-N. The sample spans a redshift range of 0.6 < z < 2.6, 24um flux densities between ~0.2-1.2 mJy, and consists of SMGs, AGN, and optically faint (z_AB > 25) sources. We find that IR luminosities derived by fitting local SEDs with 24um photometry alone are well matched to those when additional mid-infrared spectroscopic and longer wavelength photometric data is used for galaxies having z < 1.4 and 24um-derived IR luminosities typically > 3x10^12 L_sun. However, for galaxies in the redshift range between 1.4 < z < 2.6, typically having 24um-derived IR luminosities > 3x10^12 L_sun, IR luminosities are overestimated by an average factor of ~5 when SED fitting with 24um photometry alone. This result arises partly due to the fact that high redshift galaxies exhibit PAH EQWs that are large compared to local galaxies of similar luminosities. Using improved estimates for the IR luminosities of these sources, we investigate whether their IR emission is found to be in excess relative to that expected based on extinction corrected UV SFRs, possibly suggesting the presence of an obscured AGN. Through a spectral decomposition of IRS spectroscopic data, we are able to isolate the fraction of IR luminosity arising from an AGN as opposed to star formation activity. This fraction is only ~30% of the total IR luminosity among the entire sample, on average. Of the sources identified as having mid-infrared excesses, half are accounted for by using proper bolometric corrections while half show the presence of obscured AGN. We do not find evidence for evolution in the FIR-radio correlation over this redshift range, although the SMGs have IR/radio ratios which are, on average, ~3 times lower than the nominal value.
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