Obscured and Unobscured Active Galactic Nuclei in the Spitzer Space Telescope First Look Survey
Obscured and Unobscured Active Galactic Nuclei in the Spitzer Space Telescope First Look Survey
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DOI：
10.1086/422816
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发表时间：
2004-05
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影响因子：
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通讯作者：
M. Lacy;L. Storrie-Lombardi;A. Sajina;P. Appleton;L. Armus;S. Chapman;P. Choi;D. Fadda;F. Fang
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文献类型：
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作者：
M. Lacy;L. Storrie-Lombardi;A. Sajina;P. Appleton;L. Armus;S. Chapman;P. Choi;D. Fadda;F. Fang
在红外线中选择活动星系核(AGN)有助于发现其光发射被尘埃熄灭的AGN。在本文中，我们使用斯皮策太空望远镜第一视调查(FLS)来评估具有与类星体相当的中红外(MIR)亮度的活动星系核的比例，以及由于尘埃遮挡而在光学类星体调查中遗漏的活动星系核的比例。我们首先使用斯隆数字巡天(SDSS)数据库来识别4°2河外FLS中的54个类星体。这些类星体凭借其强烈的红色连续体在和平号颜色空间中占据了一个独特的区域。这使我们能够定义用于选择AGN候选的MIR颜色标准。大约有2000个FLS天体的颜色与它们是活动星系核的颜色一致，但大多数在MIR中比SDSS类星体要暗得多，后者通常有8μm的通量密度S8.0∼1mJy。我们研究了43个具有S8.0≥1mJy的物体的性质，这些物体满足我们的活动星系核颜色选择。这个样本应该既包含未被遮挡的类星体，也包含由于光学消光而没有出现在SDSS调查中的活动星系核。从最初的43个样本中去掉16个已知类星体、3个可能的正常类星体和8个虚假或混淆的天体后，我们剩下的16个天体很可能是被遮挡的类星体或发光的塞弗特2星系。这表明在S8.0∼1mJy的MIR中选择的样品中模糊和非模糊活动星系核的数量是相似的。
Selection of active galactic nuclei (AGNs) in the infrared facilitates the discovery of AGNs whose optical emission is extinguished by dust. In this paper, we use the Spitzer Space Telescope First Look Survey (FLS) to assess the fraction of AGNs with mid-infrared (MIR) luminosities that are comparable to quasars and that are missed in optical quasar surveys because of dust obscuration. We begin by using the Sloan Digital Sky Survey (SDSS) database to identify 54 quasars within the 4 deg2 extragalactic FLS. These quasars occupy a distinct region in MIR color space by virtue of their strong, red continua. This has allowed us to define an MIR color criterion for selecting AGN candidates. About 2000 FLS objects have colors that are consistent with them being AGNs, but most are much fainter in the MIR than the SDSS quasars, which typically have 8 μm flux densities S8.0 ∼ 1 mJy. We have investigated the properties of 43 objects with S8.0 ≥ 1 mJy that satisfy our AGN color selection. This sample should contain both unobscured quasars as well as AGNs that are absent from the SDSS survey because of extinction in the optical. After removing 16 known quasars, three probable normal quasars, and eight spurious or confused objects from the initial sample of 43, we are left with 16 objects that are likely to be obscured quasars or luminous Seyfert 2 galaxies. This suggests that the numbers of obscured and unobscured AGNs are similar in samples selected in the MIR at S8.0 ∼ 1 mJy.