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arXiv 0709.2046astro-ph
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在透镜星系团后面发现的ERO:II.基于多波长观测的经验性质、分类和SED模拟

EROs found behind lensing clusters: II.Empirical properties, classification, and SED modelling based on multi-wavelength observations

A. Hempel, D. Schaerer, E. Egami, R. Pelló, M. Wise, J. Richard, J. -F. Le Borgne, J. -P. Kneib

摘要:

我们研究了在两个透镜星系团后面发现的极红星系(ERO,R-K> 5.6)的性质和性质,并将它们与其他已知的星系群进行了比较。新的HST/ACS观测,斯皮策IRAC和MIPS,以及钱德拉/ACIS对两个透镜星系团Abell 1835和AC 114的观测,考虑了我们早期的光学和近红外观测,并已被用于研究这些深场中的极红天体(ERO)。我们在Abell 1835和AC 114中发现了6个和9个ERO。这些物体中的几个(7)在I和/或z波段都没有被探测到,因此是"光学"漏源。我们的大多数源(80%)的光度红移为z~0.7 - 1.5。根据简单的色图,我们的大多数天体都可以被归类为古老的恒星星族。然而,其中有几个明显的尘埃星爆的迹象。这些天体对应于R-K色中最极端的天体。当K <20.5时,(R-K> 5.6)的ERO表面密度为(0.97 ± 0.31)arcmin-2。在我们的15个ERO中,有6个(40%)也被归类为遥远的红星系(DRG)。13个具有可用IRAC光度测定的ERO中有11个也符合Yan等人(2004)的IRAC选定ERO(IERO)的选择标准。SED模型显示,我们样本中约36%的IERO是发光或超亮红外星系((U)LIRG)。一些非常红的DRG被发现是非常尘埃的星爆,甚至是(U)LIRG,也被它们的中红外测光支持。没有发现活动星系核的迹象,尽管不能排除所有天体的微弱活动。从中红外线和X射线数据来看,有5个天体被明确归类为星爆。导出的性质与DRG和IERO的性质非常相似,除了5个颜色极端的天体,发现它们的消光系数非常高(Av> 3)。

英文摘要:

We study the properties and nature of extremely red galaxies (ERO, R-K>5.6) found behind two lensing clusters and compare them with other known galaxy populations. New HST/ACS observations, Spitzer IRAC and MIPS, and Chandra/ACIS observations of the two lensing clusters Abell 1835 and AC114 contemplate our earlier optical and near-IR observations and have been used to study extremely red objects (EROs) in these deep fields. We have found 6 and 9 EROs in Abell 1835 and AC114. Several (7) of these objects are undetected up to the I and/or z band, and are hence ``optical'' drop-out sources. The photometric redshifts of most of our sources (80%) are z~0.7-1.5. According to simple colour-colour diagrams the majority of our objects would be classified as hosting old stellar populations. However, there are clear signs of dusty starbursts for several among them. These objects correspond to the most extreme ones in R-K colour. We estimate a surface density of (0.97+-0.31) arcmin-2 for EROs with (R-K>5.6) at K<20.5. Among our 15 EROs 6 (40 %) also classify as distant red galaxies (DRGs). 11 of 13 EROs with available IRAC photometry also fulfil the selection criteria for IRAC selected EROs (IEROs) of Yan et al. (2004). SED modelling shows that ~ 36 % of the IEROs in our sample are luminous or ultra-luminous infrared galaxies ((U)LIRG). Some very red DRGs are found to be very dusty starbursts, even (U)LIRGs, as also supported by their mid-IR photometry. No indication for AGNs is found, although faint activity cannot be excluded for all objects. From mid-IR and X-ray data 5 objects are clearly classified as starbursts. The derived properties are quite similar to those of DRGs and IEROs, except for 5 extreme objects in terms of colours, for which a very high extinction (Av>3) is found.

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