首次系统搜索高红移氧线团：揭示AGN反馈和恒星形成猝灭
First Systematic Search for Oxygen-Line Blobs at High Redshift: Uncovering AGN Feedback and Star-Formation Quenching
摘要：
我们在斯巴鲁-XMM深空巡天（SXDS）的0.62度^2天区，利用深窄带成像技术，以1.9x10^5 Mpc ^3的巡天体积，首次系统地搜寻了z=1.2的扩展金属线[OII]λλ 3726、3729星云或[OII]团块（OIIB）。我们发现了一个巨大的OLIB，被称为“OLIB 1”，其空间范围超过~75 kpc，光谱红移z=1.18，并且还确定了总共12个大小>30 kpc的OLIB。我们的光谱在6σ水平上呈现[NeV]λ3426线，表明该天体具有一个被遮蔽的2型活动星系核。在这个天体中存在气体流出，这是由两个边缘检测到的Fe II λ2587吸收和Fe II *λ2613发射线，这两条线都是蓝移的，高达500-600 km/s，表明OlIB 1的热源是活动星系核或相关的冲击激发，而不是由恒星爆发产生的超新星。在z~1.2处，OLIB 1型巨型团块的数密度估计为~ 5 × 10 ^{-6} Mpc^{-3}，这与在类似红移处驱动外流的活动星系核的数密度相当，表明巨型OLIB仅由活动星系核活动产生。另一方面，小OIIB的数密度为6 × 10 ^{-5} Mpc^{-3}，与相同M_B范围内蓝云中z~1星系的数密度相比，可能意味着z~1处3%的恒星形成星系通过涉及扩展[OII]发射的流出来淬灭恒星形成。
英文摘要：
We present the first systematic search for extended metal-line [OII]λλ3726,3729 nebulae, or [OII] blobs (OIIBs), at z=1.2 using deep narrowband imaging with a survey volume of 1.9x10^5 Mpc^3 on the 0.62 deg^2 sky of Subaru-XMM Deep Survey (SXDS) field. We discover a giant OIIB, dubbed 'OIIB 1', with a spatial extent over ~75 kpc at a spectroscopic redshift of z=1.18, and also identify a total of twelve OIIBs with a size of >30 kpc. Our optical spectrum of OIIB 1 presents [NeV]λ3426 line at the 6σ level, indicating that this object harbors an obscured type-2 AGN. The presence of gas outflows in this object is suggested by two marginal detections of FeIIλ2587 absorption and FeII*λ2613 emission lines both of which are blueshifted at as large as 500-600 km/s, indicating that the heating source of OIIB 1 is AGN or associated shock excitation rather than supernovae produced by starbursts. The number density of OIIB 1-type giant blobs is estimated to be ~5x10^{-6} Mpc^{-3} at z~1.2, which is comparable with that of AGNs driving outflow at a similar redshift, suggesting that giant OIIBs are produced only by AGN activity. On the other hand, the number density of small OIIBs, 6x10^{-5} Mpc^{-3}, compared to that of z~1 galaxies in the blue cloud in the same M_B range, may imply that 3% of star-forming galaxies at z~1 are quenching star formation through outflows involving extended [OII] emission.
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