2014ApJ...794..129H

We report our Keck/MOSFIRE and Magellan/Low-Dispersion Survey Spectrograph spectroscopy for an [O II] Blob, O II B10, that is a high-z galaxy with spatially extended [O II] λλ3726, 3729 emission over 30 kpc recently identified by a Subaru large-area narrowband survey. The systemic redshift of O II B10 is z = 1.18 securely determined with [O III] λλ4959, 5007 and Hβ emission lines. We identify Fe II λ2587 and Mg II λλ2796, 2804 absorption lines blueshifted from the systemic redshift by 80±50 and 260±40 km/s, respectively, which indicates gas outflow from O II B10 with the velocity of ∼80-260 km/s. This outflow velocity is comparable with the escape velocity, 250±140 km/s, estimated under the assumption of a singular isothermal halo potential profile. Some fraction of the outflowing gas could escape from the halo of O II B10, suppressing O II B10's star-formation (SF) activity. We estimate a mass loading factor, η, that is a ratio of mass outflow rate to SF rate, and obtain η > 0.8±0.1, which is relatively high compared with low-z starbursts including U/LIRGs and active galactic nuclei (AGNs). The major energy source of the outflow is unclear with the available data. Although no signature of AGNs is found in the X-ray data, O II B10 falls in the AGN/star-forming composite region in the line diagnostic diagrams. It is possible that the outflow is powered by SF and a type-2 AGN with narrow FWHM emission line widths of 70-130 km/s. This is the first detailed spectroscopic study of oxygen-line blobs that includes analyses of the escape velocity, the mass loading factor, and the presence of an AGN, and is a significant step to understanding the nature of oxygen-line blobs and the relation between gas outflow and SF quenching at high redshift.