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arXiv 0910.2464astro-ph.CO
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亚毫米选择星系的X射线性质

On the X-ray properties of submm-selected galaxies

Elise S. Laird, Kirpal Nandra, Alexandra Pope, Douglas Scott

摘要:

本文分析了CDF-N中35个亚毫米星系的X射线性质。使用一个强大的850微米选定的星系的样本,从斯皮策和/或无线电同行的准确位置,我们发现16个对象(45+/-8%)与显着的X射线探测在2 Ms钱德拉数据。其中6个SMG(~17+/-6%)测量到的X射线光度或上限与基于远红外(FIR)或射电衍生恒星形成率(SFR)的预期一致,因此X射线仅来自恒星形成。在另外7个源(20+/-7%)中,活动星系核对X射线发射的贡献占主导地位,而在另外3个源中,尚不清楚是恒星过程还是吸积造成的。未检出的X射线SMG的叠加显示出高度显著的检出。如果是由于恒星形成,这相当于平均X射线导出的SFR约为150 Msun/yr。根据X射线观测结果,我们推断活动星系核在SMG中所占的比例为20-29(+/-7)%,这接近以前估计的下限。光谱分析表明,一般来说,SMG在X射线中的遮蔽程度并不严重,但大多数被归类为活动星系核的SMG对NH的吸收都超过了10 ^22 cm^-2。在安全活动星系核中,只有3个星系核的热光度是由活动星系核支配的。在~85%的SMG中,X射线谱有效地排除了活动星系核对辐射热辐射的贡献,即使活动星系核是康普顿厚度的。因此,有证据表明,强烈的恒星形成解释了大多数SMG中的FIR和X射线发射。我们认为,而不是有一个特别高的活动星系核的分数或占空比,SMG有一个很高的X射线探测率在非常微弱的流量,部分是因为他们的高恒星形成率,在罕见的情况下,因为submm发射是从活动星系核。(节略)

英文摘要:

We present an analysis of the X-ray properties of 35 submm galaxies(SMGs) in the CDF-N. Using a sample of robust 850micron-selected galaxies, with accurate positions from Spitzer and/or radio counterparts, we find 16 objects (45+/-8%) with significant X-ray detections in the 2Ms Chandra data. 6 of these SMGs (~17+/-6%) have measured X-ray luminosities or upper limits consistent with those expected based on the far-infrared (FIR) or radio-derived star formation rate (SFR), and hence with the X-rays coming solely from star formation. In another 7 sources (20+/-7%) a dominant AGN contribution to the X-ray emission is required, while in 3 more it is unclear whether stellar process or accretion are responsible. Stacking of the X-ray undetected SMGs reveals a highly significant detection. If due to star formation, this corresponds to an average X-ray derived SFR of ~150 Msun/yr. We deduce that the AGN fraction in SMGs based on X-ray observations is 20-29 (+/-7) %, which is towards the lower limit of previous estimates. Spectral analysis shows that in general the SMGs are not heavily obscured in the X-ray but most of the SMGs classfied as AGN show absorption with N_H in excess of 10^22 cm^-2. Of the secure AGN, the bolometric luminosity appears to be dominated by the AGN in only 3 cases. In ~85% of the SMGs, the X-ray spectrum effectively rules out an AGN contribution that dominates the bolometric emission, even if the AGN is Compton thick. The evidence therefore suggests that intense star formation accounts for both the FIR and X-ray emission in most SMGs. We argue that, rather than having an especially high AGN fraction or duty cycle, SMGs have a high X-ray detection rate at very faint fluxes partly because of their high star formation rates and, in rarer cases, because the submm emission is from an AGN.(abridged)

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