AN EXTREME METALLICITY, LARGE-SCALE OUTFLOW from A STAR-FORMING GALAXY at z ∼ 0.4

Abstract

We present a detailed analysis of a large-scale galactic outflow in the circumgalactic medium of a massive (Mh 10 M ∼12.5 M⊙), star-forming (∼6.9 M⊙yr-1), sub-L∗( ∼0.5LB∗) galaxy at z = 0.39853 that exhibits a wealth of metal-line absorption in the spectra of the background quasar Q 0122-003 at an impact parameter of 163 kpc. The galaxy inclination angle (i = 63�) and the azimuthal angle (Φ = 73�) imply that the QSO sightline is passing through the projected minor-axis of the galaxy. The absorption system shows a multiphase, ulticomponent structure with ultra-strong, wide velocity spread O VI (log N = 15.16�0.04, Δv90 = 419 km s-1) and N V (log N = 14.69�0.07, Δv90 = 285 km s-1) lines that are extremely rare in the literature. The highly ionized absorption components are well explained as arising in a low density (∼10-4.2 cm-3), diffuse (∼10 kpc), cool (∼104 K) photoionized gas with a super-solar metallicity ([X H] ≳0.3). From the observed narrowness of the Lyβ profile, the non-detection of S IV absorption, and the presence of strong C IV absorption in the low-resolution FOS spectrum, we rule out equilibrium/non-equilibrium collisional ionization models. The low-ionization photoionized gas with a density of ∼10-2.5 cm-3 and a metallicity of [X H] ≳-1.4 is possibly tracing recycled halo gas. We estimate an outflow mass of ∼2x1010M⊙a mass-flow rate of ∼54 M⊙ yr-1, a kinetic luminosity of ∼9x1041 erg s-1, and a mass loading factor of ∼8 for the outflowing high-ionization gas. These are consistent with the properties of down-the-barrel outflows from infrared-luminous starbursts as studied by Rupke et al. Such powerful, large-scale, metal-rich outflows are the primary means of sufficient mechanical and chemical feedback as invoked in theoretical models of galaxy formation and evolution.