平衡能量收支：高红移红外发光星系中恒星形成与AGN
Balancing the Energy Budget: Star-Formation versus AGN in High Redshift Infrared Luminous Galaxies
摘要：
我们提出了深{ \it斯皮策}中红外光谱，以及16，24，70和850\，$\micron$ \测光，位于大天文台起源深巡天北（GOODS-N）领域的22个星系。样品的红移范围为$0.6\la z \la 2.6$，24~ $μ$ m的通量密度介于$\sim$ 0.2 $-$ 1.2 mJ y之间，由亚毫米星系（SMG）、X射线或光学选择的活动星系核（AGN）和光学暗淡（$z_{AB}>25$ \，mag）源组成。我们发现，红外（IR;对于具有$z\la1.4$和24-$\micron$衍生的红外光度典型值为$\la 3\times 10^{12}~L_{\sun}$的星系，通过单独用24-$\micron$光度法拟合局部光谱能量分布（SED）而得到的$8-1000~\micron$）光度与使用额外的中红外光谱和较长波长光度数据时得到的光度很好地匹配。然而，对于红移范围在$1.4\la z \la 2.6$之间的星系，通常具有由24~ $\micron$导出的红外光度$\ga 3\times 10^{12}~L_{\sun}$，当SED单独与24~ $\micron$光度学拟合时，红外光度被高估了平均因子$\sim$ 5.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的芳香特征等效宽度是大的本地星系相比，类似的光度。通过中红外光谱数据的光谱分解，我们能够分离出的红外光度部分所产生的活动星系核，而不是恒星形成活动。该部分仅占整个样品中总IR光度的$\sim$ 30%。
英文摘要：
We present deep {\it Spitzer} mid-infrared spectroscopy, along with 16, 24, 70, and 850\,$\micron$\ photometry, for 22 galaxies located in the Great Observatories Origins Deep Survey-North (GOODS-N) field. The sample spans a redshift range of $0.6\la z \la 2.6$, 24~$μ$m flux densities between $\sim$0.2$-$1.2 mJy, and consists of submillimeter galaxies (SMGs), X-ray or optically selected active galactic nuclei (AGN), and optically faint ($z_{AB}>25$\,mag) sources. We find that infrared (IR; $8-1000~\micron$) luminosities derived by fitting local spectral energy distributions (SEDs) with 24~$\micron$ photometry alone are well matched to those when additional mid-infrared spectroscopic and longer wavelength photometric data is used for galaxies having $z\la1.4$ and 24~$\micron$-derived IR luminosities typically $\la 3\times 10^{12}~L_{\sun}$. However, for galaxies in the redshift range between $1.4\la z \la 2.6$, typically having 24~$\micron$-derived IR luminosities $\ga 3\times 10^{12}~L_{\sun}$, IR luminosities are overestimated by an average factor of $\sim$5 when SED fitting with 24~$\micron$ photometry alone. This result arises partly due to the fact that high redshift galaxies exhibit aromatic feature equivalent widths that are large compared to local galaxies of similar luminosities. Through a spectral decomposition of mid-infrared 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 able to account for $\sim$30\% of the total IR luminosity among the entire sample.
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