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arXiv 1105.0602astro-ph.GA
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大质量星系团0 < z < 1.3的中红外选择活动星系核普查

A Census of Mid-Infrared Selected Active Galactic Nuclei in Massive Galaxy Clusters at 0 < z < 1.3

Adam R. Tomczak, Kim-Vy H. Tran, Amélie Saintonge

摘要:

利用Spitzer/IRAC测光技术和中红外色选技术,对9个大质量星系团(0<z<1.3)进行了深中红外普查,共获得约1500个光谱确认的成员星系。在四个IRAC通道中至少有三个在>3 sigma水平上检测到的949个星系团中,我们确定了12个拥有中红外选择活动星系核(IR-AGN)。为了在我们的红移范围内比较IR-AGN,我们定义了两个完整的星系团样本:(1)静止坐标系V(AB)星等<-21.5的光选成员和(2)亮于(M*+0.5)的中红外选择成员,即本质上是恒星质量切割。在两个样品中,我们测量到\agnfrac ~1%,在z<1时具有~3%的强上限。在z<1时,这种一致低的IR-AGN比例是令人惊讶的,因为在相同的星系团中,24微米的源的比例从z~0到z~1增加了大约四倍;这表明大多数检测到的24微米通量是由于恒星的形成。只有在我们的z=1.24的单个星系团中,IR-AGN的比例才可测量到更高,约为15%(所有成员;仅晚期类型约为70%)。与最近的研究一致,我们发现星系团IR-AGN主要由具有蓝色光学颜色的晚型星系,即最近/正在形成恒星的成员。四个最明亮的红外活动星系核也是X射线源;这些红外+X射线活动星系核都位于星系团核心之外(Rproj>0.5 Mpc),并且由高度形态扰动的成员所承载。虽然我们的样本是有限的,我们的研究结果表明,\agnfrac在大质量星系团是不强相关的恒星形成在z<1,和IR-AGN有一个更突出的作用在z>1。

英文摘要:

We conduct a deep mid-infrared census of nine massive galaxy clusters at (0<z<1.3) with a total of ~1500 spectroscopically confirmed member galaxies using Spitzer/IRAC photometry and established mid-infrared color selection techniques. Of the 949 cluster galaxies that are detected in at least three of the four IRAC channels at the >3 sigma level, we identify 12 that host mid-infrared selected active galactic nuclei (IR-AGN). To compare the IR-AGN across our redshift range, we define two complete samples of cluster galaxies: (1) optically-selected members with rest-frame V(AB) magnitude <-21.5 and (2) mid-IR selected members brighter than (M*+0.5), i.e. essentially a stellar mass cut. In both samples, we measure \agnfrac ~1% with a strong upper limit of ~3% at z<1. This uniformly low IR-AGN fraction at z<1 is surprising given the fraction of 24 micron sources in the same galaxy clusters is observed to increase by about a factor of four from z~0 to z~1; this indicates that most of the detected 24 micron flux is due to star formation. Only in our single galaxy cluster at z=1.24 is the IR-AGN fraction measurably higher at ~15% (all members; ~70% for late-types only). In agreement with recent studies, we find the cluster IR-AGN are predominantly hosted by late-type galaxies with blue optical colors, i.e. members with recent/ongoing star formation. The four brightest IR-AGN are also X-ray sources; these IR+X-ray AGN all lie outside the cluster core (Rproj>0.5 Mpc) and are hosted by highly morphologically disturbed members. Although our sample is limited, our results suggest that \agnfrac in massive galaxy clusters is not strongly correlated with star formation at z<1, and that IR-AGN have a more prominent role at z>1.

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