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arXiv 1006.2873astro-ph.CO
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z ~ 1-2波段LIRGs和ULIRGs的超深Spitzer中红外光谱

Ultra-deep Spitzer Mid-Infrared Spectroscopy of LIRGs and ULIRGs at z ~ 1-2

D. Fadda, L. Yan, G. Lagache, A. Sajina, D. Lutz, S. Wuyts, D. T. Frayer, D. Marcillac, E. Le Floc'h, K. Caputi, H. W. W. Spoon, S. Veilleux, A. Blain, G. Helou

摘要:

我们目前的超深中红外光谱的48个红外发光星系的GOODS-South领域所获得的斯皮策太空望远镜的红外光谱仪(IRS)。这些星系是从两个红移仓(0.76-1.05和1.75-2.4)中的微弱红外源(0.14 - 0.5 mJy,24 μ m)中选出的,以在最活跃的时期对宇宙红外背景的主要贡献者进行采样。我们估计92%的样品使用PAH和Si吸收功能的红移。这些星系中只有少数(z~1处5%,z~2处12%)的总红外光度由活动星系核的发射主导。z~1 LIRGs和z~ 2ULIRGs的平均中红外光谱分别与局域星暴和类HII ULIRGs的平均光谱非常相似。我们发现,6.2 μ m PAH等效宽度达到一个平台~1 μ m的L(24 μ)<1 E11 L(太阳)。在较高的光度下,EW(6.2 μ)与L(24 μ m)反相关。有趣的是,高z ULIRG和SMG位于当地EW(6.2 μ m)- L(24 μ m)的关系,这表明,在给定的光度,高z ULIRG有活动星系核的贡献,他们的尘埃排放低于当地同行。对它们形态的定量分析表明,在相同的红移下,大多数亮红外星系的形态与静红外星系相似。所有z~ 2ULIRG都是IR过剩的BzK星系,在给定的UV斜率下,它们的L(FIR)/L(1600 A)比值大多高于星暴星系。"红外过量“(Daddi等人,2007年)主要是由于7.7微米多环芳烃的强烈排放和对紫外尘埃消光的低估。基于直接从中红外光谱测量的活动星系核动力L(6 μ m)连续谱,我们估计活动星系核的平均内在X射线光度为L(2-10 keV)=(0.1 +/- 0.6)1 E43 erg/s,这个值大大低于Daddi等人(2007)的预测。

英文摘要:

We present ultra-deep mid-IR spectra of 48 infrared-luminous galaxies in the GOODS-South field obtained with the InfraRed Spectrograph (IRS) on the Spitzer Space Telescope. These galaxies are selected among faint infrared sources (0.14 - 0.5 mJy at 24 um) in two redshift bins (0.76-1.05 and 1.75-2.4) to sample the major contributors to the cosmic infrared background at the most active epochs. We estimate redshifts for 92% of the sample using PAH and Si absorption features. Only few of these galaxies (5% at z~1 and 12% at z~2) have their total infrared luminosity dominated by emission from AGN. The averaged mid-IR spectra of the z~1 LIRGs and of the z~2 ULIRGs are very similar to the averaged spectrum of local starbursts and HII-like ULIRGs, respectively. We find that 6.2um PAH equivalent widths reach a plateau of ~1 um for L(24 mu) < 1E11 L(sun). At higher luminosities, EW (6.2 mu) anti-correlates with L(24 um). Intriguingly, high-z ULIRGs and SMG lie above the local EW (6.2 um) - L(24 um) relationship suggesting that, at a given luminosity, high-z ULIRGs have AGN contributions to their dust emission lower than those of local counterparts. A quantitative analysis of their morphology shows that most of the luminous IR galaxies have morphologies similar to those of IR-quiet galaxies at the same redshift. All z~2 ULIRGs of our sample are IR-excess BzK galaxies and most of them have L(FIR)/L(1600A) ratios higher than those of starburst galaxies at a given UV slope. The ``IR excess'' (Daddi et al. 2007) is mostly due to strong 7.7 um PAH emission and under-estimation of UV dust extinction. On the basis of the AGN-powered L (6 um) continuum measured directly from the mid-IR spectra, we estimate an average intrinsic X-ray AGN luminosity of L(2-10 keV) = (0.1 +/- 0.6) 1E43 erg/s, a value substantially lower than the prediction by Daddi et al. (2007).

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