NDWFS Boots场中Z=2.78的UV超亮Lyman Break星系
A UV Ultra-luminous Lyman Break Galaxy at Z=2.78 in NDWFS Bootes Field
摘要：
我们提出了一个最紫外（UV）发光莱曼Break Galeries（LBG）（J1432+3358）在z=2.78，发现在NOAO深宽视场调查（NDWFS）Bootes领域。J1432+3358的R带星等为22.29 AB，比这个红移的典型L* LBG亮2等以上。深z波段图像显示了J1432+3358的两个分量，它们相隔1.0”，通量比为3：1。高信噪比（S/N）的静止坐标系紫外光谱显示出Lya发射线和星际介质吸收线。NV和CIV发射线的缺失，X射线和射电波长以及中红外（MIR）颜色的未检测表明该星系中没有或弱活动星系核（AGN）（<10%）。该星系具有比典型z~3长带星系更宽的线轮廓，半高宽约为1000 km/s，流出速度约为500 km/s。通过拟合光谱能量分布（SED）与恒星合成模型的物理性质。尘埃消光系数E（B-V）=0.12，与正常LBG相似。由SED拟合得到的恒星形成率与经尘埃校正的紫外辐射通量一致，约为300 Msun/yr，恒星质量为1.3e11 Msun。J1432+3358的SFR和恒星质量比正常的LBG高一个数量级。SED拟合结果支持J1432+3358具有连续的恒星形成历史，其恒星形成期为6.3亿年。J1432+3358的形貌和物理性质表明，J1432+3358处于3：1合并过程的早期阶段。独特的性质和低的空间数密度（~ 1 e-7 Mpc^{-3}）与这样的解释是一致的，即这样的星系要么是在恒星形成的一个短暂的未被遮蔽的阶段发现的，要么是一小部分密集的恒星形成星系是未被遮蔽的。
英文摘要：
We present one of the most ultraviolet (UV) luminous Lyman Break Galaxies (LBGs) (J1432+3358) at z=2.78, discovered in the NOAO Deep Wide-Field Survey (NDWFS) Bootes field. The R-band magnitude of J1432+3358 is 22.29 AB, more than two magnitudes brighter than typical L* LBGs at this redshift. The deep z-band image reveals two components of J1432+3358 separated by 1.0" with flux ratio of 3:1. The high signal-to-noise ratio (S/N) rest-frame UV spectrum shows Lya emission line and interstellar medium absorption lines. The absence of NV and CIV emission lines, the non-detection in X-ray and radio wavelengths and mid-infrared (MIR) colors indicate no or weak active galactic nuclei (AGN) (<10%) in this galaxy. The galaxy shows broader line profile with the full width half maximum (FWHM) of about 1000 km/s and larger outflow velocity (~500 km/s) than those of typical z~3 LBGs. The physical properties are derived by fitting the spectral energy distribution (SED) with stellar synthesis models. The dust extinction, E(B-V)=0.12, is similar to that in normal LBGs. The star formation rates (SFRs) derived from the SED fitting and the dust-corrected UV flux are consistent with each other, ~300 Msun/yr, and the stellar mass is 1.3e11 Msun. The SFR and stellar mass in J1432+3358 are about an order of magnitude higher than those in normal LBGs. The SED-fitting results support that J1432+3358 has a continuous star formation history with the star formation episode of 630 Myr. The morphology of J1432+3358 and its physical properties suggest that J1432+3358 is in an early phase of 3:1 merger process. The unique properties and the low space number density (~1e-7 Mpc^{-3})are consistent with the interpretation that such galaxies are either found in a short unobscured phase of the star formation or that small fraction of intensive star-forming galaxies are unobscured.
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