In merger-driven models of massive galaxy evolution, the luminous quasar phase is expected to be accompanied by vigorous star formation in quasar host galaxies. In this paper, we use high column density damped Lyα (DLA) systems along quasar sight lines as natural coronagraphs to directly study the far-UV (FUV) radiation from the host galaxies of luminous background quasars. We have stacked the spectra of ~2000 DLA systems (N H I 1020.6?cm–2) with a median absorption redshift z = 2.6 selected from quasars observed in the SDSS-III Baryon Oscillation Spectroscopic Survey. We detect residual flux in the dark troughs of the composite DLA spectra. The level of this residual flux significantly exceeds systematic errors in the Sloan Digital Sky Survey fiber sky subtraction; furthermore, the residual flux is strongly correlated with the continuum luminosity of the background quasar, while uncorrelated with DLA column density or metallicity. We conclude that the flux could be associated with the average FUV radiation from the background quasar host galaxies (with medium redshift z = 3.1) that is not blocked by the intervening DLA. Assuming that all of the detected flux originates from quasar hosts, for the highest quasar luminosity bin (L =?2.5?× 1013 L ☉), the host galaxy has an FUV intensity of 1.5 ± 0.2 × 1040?erg?s–1 ?–1; this corresponds to an unobscured UV star formation rate of 9 M ☉?yr–1.
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机译：在合并驱动的大规模星系演化模型中，预计类星体宿主星系会伴随着发光的类星体相伴随剧烈的恒星形成。在本文中，我们使用沿类星体视线的高列密度衰减Lyα（DLA）系统作为自然日冕仪，直接研究了来自发光背景类星体宿主星系的远紫外线（FUV）辐射。我们堆积了〜2000个DLA系统的光谱（N H I> 1020.6？cm–2），中位吸收红移z = 2.6，选自SDSS-III重子振荡光谱调查中观察到的类星体。我们检测到复合DLA光谱的暗槽中的残留通量。剩余通量的水平大大超过了Sloan Digital Sky Survey光纤天空减法中的系统误差;此外，残余通量与背景类星体的连续光度密切相关，而与DLA柱密度或金属性无关。我们得出的结论是，通量可能与背景类星体宿主星系的平均FUV辐射有关（中间红移z = 3.1），而中间DLA不受其干扰。假设所有检测到的通量都来自类星体，那么对于最高类星体的光度箱（L =？2.5？×1013 L☉），宿主星系的FUV强度为1.5±0.2×1040？erg？s–1？。 –1;这对应于9 M yryr-1的无遮盖的UV星形成速率。
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