Using VO tools to investigate distant radio starbursts hosting obscured AGN in the HDF(N) region
A. M. S. Richards, T. W. B. Muxlow, R. Beswick, M. G. Allen, K. Benson, R. C. Dickson, M. A. Garrett, S. T. Garrington, E. Gonzalez-Solarez, P. A. Harrison, A. … 展开作者
A. M. S. Richards, T. W. B. Muxlow, R. Beswick, M. G. Allen, K. Benson, R. C. Dickson, M. A. Garrett, S. T. Garrington, E. Gonzalez-Solarez, P. A. Harrison, A. J. Holloway, M. M. Kettenis, R. A. Laing, E. A. Richards, H. Thrall, H. J. van Langevelde, N. A. Walton, P. N. Wilkinson, N. Winstanley, .
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24 pages, 12 figures, uses graphicx, rotating, natbib, supertabular packages and aa.cls. Accepted for publication in A&A
A 10-arcmin field around the HDF(N) contains 92 radio sources >40 uJy, resolved by MERLIN+VLA at 0".2-2".0 resolution. 55 have Chandra X-ray counterparts including 18 with a hard X-ray photon index and high luminosity characteristic of a type-II (obscured) AGN. >70% of the radio sources have been classified as starbursts or AGN using radio morphologies, spectral indices and comparisons with optical appearance and MIR emission. Starbursts outnumber radio AGN 3:1. This study extends the VO methods previously used to identify X-ray-selected obscured type-II AGN to investigate whether very luminous radio and X-ray emission originates from different phenomena in the same galaxy. The high-redshift starbursts have typical sizes of 5--10 kpc and star formation rates of ~1000 Msun/yr. There is no correlation between radio and X-ray luminosities nor spectral indices at z>~1.3. ~70% of both the radio-selected AGN and the starburst samples were detected by Chandra. The X-ray luminosity indicates the presence of an AGN in at least half of the 45 cross-matched radio starbursts, of which 11 are type-II AGN including 7 at z>1.5. This distribution overlaps closely with the X-ray detected radio sources which were also detected by SCUBA. Stacked 1.4-GHz emission at the positions of radio-faint X-ray sources is correlated with X-ray hardness. Most extended radio starbursts at z>1.3 host X-ray selected obscured AGN. Radio emission from most of these ultra-luminous objects is dominated by star formation but it contributes less than 1/3 of their X-ray luminosity. Our results support the inferences from SCUBA and IR data, that at z>1.5, star formation is an order of magnitude more extended and more copious, it is closely linked to AGN activity and it is triggered differently, compared with star formation at lower redshifts.
Low Star Formation Rates for z=1 Early-Type Galaxies in the Very Deep GOODS-MIPS Imaging: Implications for their Optical/Near-Infrared Spectral Energy Distributions
我们测量了z~1早型星系中的遮蔽恒星形成。这限制了恒星形成对它们的光学/近红外颜色的影响，我们发现，这些颜色比Bruzual和Charlot（2003）的模型预测的要红。从深ACS成像中，我们构建了一个样本的95个形态选择的早型星系的HDF-N和CDF-S的光谱红移范围为0.85 <z 2 sigma检测（~25 μ J）为17（-4，+9）%。<1.15. We measure their 24 micron fluxes from the deep GOODS-MIPS imaging and derive the IR luminosities and star formation rates. The fraction of galaxies with >在15个有显著探测的星系中，至少有6个有活动星系核。将没有明显探测到的星系的MIPS图像叠加起来，再加上没有活动星系核的已探测星系，我们发现平均恒星形成速率（SFR）的上限为5.2 +/-3.0 Msol yr ^-1，平均比SFR的上限为4.6 +/-2.2 * 10 ^-11 yr ^-1。在假设平均SFR将以宇宙平均速率下降的情况下，早型星系人口的恒星质量在z = 1和现在之间的原位增长小于14 +/-7%。我们发现，典型的低红外光度和SFR意味着模糊的恒星形成（或AGN）的影响，其静止框架的光学/近红外SED…
我们提出了广泛的意见的样本遥远的，submm星系检测领域的大规模集群透镜，A1835，使用SCUBA。结合早期对其他亚毫米级选定源的观测（Ivison et al. 1998; Smail et al. 1999; Soucail et al. 1999），我们现在对7个亚毫米级源进行了详细的多波长观测，利用了集群透镜的消色差放大和大量的档案数据集。这些来源，都清楚地在z > 1，说明了在遥远的submm选择星系的无线电和光学特性的范围很广。我们包括第一个候选人的“纯”星暴submm星系在高红移，z=2.56相互作用的星系，没有明显的迹象，主办活动星系核的详细观测。其余的源有不同程度的推断活动星系核活动（3从7最明亮的显示活动星系核的存在的一些证据），虽然即使活动星系核是明显存在的，它仍然是不明显的，如果再处理的辐射从这个源占主导地位的submm发射。与光谱性质的变化相反，我们看到人口相对均匀的形态，合并或相互作用的系统的一大部分。我们的研究表明，几乎相同的SEDs被认为是表现出显着不同的光学/紫外光谱线特性的星系。我们的结论是，标准的光学/紫外光谱分类在应用于遥远的、高度模糊的星系时具有误导性，我们必须寻求其他方法来确定对亚毫米星系总体能量预算的各种贡献，从而对远红外河外背景的贡献。
