An Extreme Metallicity, Large-scale Outflow from a Star-forming Galaxy at z ~ 0.4

We present a detailed analysis of a large-scale galactic outflow in the circumgalactic medium of a massive ({M}_{{h}}∼ {10}^12.5 {M}_⊙ ), star-forming (∼ 6.9 {M}_⊙ yr^-1), sub-L_* (∼ 0.5{L}_B^*) 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^\circ ) and the azimuthal angle ({{Φ }}=73^\circ ) imply that the QSO sightline is passing through the projected minor-axis of the galaxy. The absorption system shows a multiphase, multicomponent structure with ultra-strong, wide velocity spread {{O}} {{VI}} ({log}N=15.16+/- 0.04, {{Δ }}{v}₉₀ = 419 km s^-1) and {{N}} {{V}} ({log}N=14.69+/- 0.07, {{Δ }}{v}₉₀ = 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 ∼ 2× {10}¹⁰ {M}_⊙ , a mass-flow rate of ∼ 54 {M}_⊙ {{yr}}^-1, a kinetic luminosity of ∼ 9× {10}⁴¹ 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.