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arXiv 0911.2004astro-ph.CO
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Abell 2218中一个新发现的z=4.04透镜亚毫米星系的物理性质和形态

Physical properties and morphology of a newly identified compact z=4.04 lensed submillimeter galaxy in Abell 2218

K. K. Knudsen, J. -P. Kneib, J. Richard, G. Petitpas, E. Egami

摘要:

我们提出了一个明亮的submm源,SMMJ 163555.5 +661300,在透镜集群Abell 2218中检测到的识别,我们已经准确地确定了位置使用观测从亚毫米阵列(SMA)。如果我们将在λ = 6140 AA处检测到的单发射线归因于莱曼α,则所识别的光学对应物具有z=4.044+-0.001的光谱红移。这种红移与光学/近红外测光红移以及亚毫米级流量比S_450/S_850~1.6,射电-亚毫米级流量比S_1.4/S_850 < 0.004,24 μ m-850 μ m流量比S_24/S_850 < 0.005是一致的。校正了~5.5的引力透镜放大率后,我们发现该源的远红外光度为1.3 × 10^12 Lsun,这意味着恒星形成速率为230 Msun/年。这使它成为迄今为止已知的z>4时光度最低的SMG。先前的CO(4-3)发射线的修正导致了一个未探测到的结果,我们由此推导出CO线光度的上限为L '_CO = 0.3 × 10^10 K km/s/pc^2,这与星暴星系的L'_CO-L_FIR关系并不矛盾。光学和近红外测光的最佳拟合模型给出的恒星星族年龄为1.4 Gyr,恒星质量为1.6x10^10 Msun。光学形态紧凑,在源平面内,星系的范围约为6 kpc x 3 kpc,单个恒星形成的结的大小小于500 pc。在SMA数据中没有解析出J163556,因此我们将星爆区的大小严格限定为8 kpc x 3 kpc,这意味着恒星形成率表面密度的下限为12 Msun/yr/kpc ^[2]。J163556的红移扩展了微弱的透镜SMG的红移分布,我们没有发现任何证据表明这些SMG的红移分布与明亮的SMG不同。

英文摘要:

We present the identification of a bright submm source, SMMJ163555.5+661300, detected in the lensing cluster Abell2218, for which we have accurately determined the position using observations from the Submillimeter Array (SMA). The identified optical counterpart has a spectroscopic redshift of z=4.044+-0.001 if we attribute the single emission line detected at lambda=6140AA to Lyman-alpha. This redshift identification is in good agreement with the optical/near-infrared photometric redshift as well as the submm flux ratio S_450/S_850~1.6, the radio-submm flux ratio S_1.4/S_850 < 0.004, and the 24um to 850um flux ratio S_24/S_850 < 0.005. Correcting for the gravitational lensing amplification of ~5.5, we find that the source has a far-infrared luminosity of 1.3x10^12 Lsun, which implies a star formation rate of 230 Msun/yr. This makes it the lowest-luminosity SMG known at z>4 to date. Previous CO(4-3) emission line obserations yielded a non-detection, for which we derived an upper limit of the CO line luminosity of L'_CO = 0.3x10^10 K km/s/pc^2, which is not inconsistent with the L'_CO - L_FIR relation for starburst galaxies. The best fit model to the optical and near-infrared photometry give a stellar population with an age of 1.4 Gyr and a stellar mass of 1.6x10^10 Msun. The optical morphology is compact and in the source plane the galaxy has an extent of ~6kpc x 3kpc with individual star forming knots of <500 pc in size. J163556 is not resolved in the SMA data and we place a strict upper limit on the size of the starburst region of 8kpc x 3kpc, which implies a lower limit on the star formation rate surface density of 12 Msun/yr/kpc^2. The redshift of J163556 extends the redshift distribution of faint, lensed SMGs, and we find no evidence that these have a different redshift distribution than bright SMGs.

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