标题： ISO-2MASS类星体巡天：关于I型源 显示英文标题

标题： The ISO-2MASS AGN survey: On the type-1 sources

摘要： 我们将ISOCAM平行模式6.7微米（LW2滤波器）巡天与2MASS全天红外巡天相结合，以期获得一种强大的工具，用来独立于尘埃消光寻找活动星系核（AGN）。利用中度颜色标准H-K>0.5和K-LW2>2.7，我们在大约10平方度的有效区域内选出77个AGN候选体。通过光学光谱学，我们发现24个（30%）红移范围为0.1<z<2.3的I型类星体；其中9个红移z>0.8。约三分之一的ISO-2MASS类星体表现出如此红的光学颜色，以至于它们在光学和紫外AGN巡天（如SDSS、2DF或HES）中被遗漏。在R<18星等范围内，ISO-2MASS类星体的空间面密度约为2 deg^(-2)，比SDSS类星体巡天的1.35 deg^(-2)多出50%，我们测得的光学-红外类星体空间面密度为2.7 deg^(-2)。由于仅有两个ISO-2MASS类星体同时满足J-K>2，因此将ISO中红外测光数据纳入显著扩展了纯2MASS红AGN巡天的能力。我们认为新发现的红色AGN类似于类星体群体中的年轻成员，并且类星体在其一生中有很大一部分时间处于尘埃包裹阶段。 显示英文摘要

摘要： We combined the ISOCAM Parallel Mode Survey at 6.7 micron (LW2 filter) with the Two Micron All Sky Survey in order to obtain a powerful tool to search for AGN independent of dust extinction. Using moderate colour criteria H-K>0.5 and K-LW2>2.7 we have selected a sample of 77 AGN candidates in an effective area of about 10 square degrees. By means of optical spectroscopy we find 24 (30%) type-1 QSOs at redshifts 0.1<z<2.3; nine of them have z>0.8. About one third of the ISO-2MASS QSOs show so red optical colours, that they are missed in optical and UV AGN surveys like SDSS, 2DF, or HES. With a surface density of about 2 deg^(-2) down to R<18 mag the ISO-2MASS QSOs outnumber the 1.35 deg^(-2) of the SDSS quasar survey by 50%; we find a combined optical-IR QSO surface density of 2.7 deg^(-2). Since only two of the ISO-2MASS QSOs have also J-K>2, the inclusion of the ISO mid-infrared photometry significantly extends the capabilities of the pure 2MASS red AGN survey. We suggest that the newly found red AGN resemble young members of the quasar population, and that quasars spend much of their lifetime in a dust enshrouded phase.