AN EXTREME METALLICITY, LARGE-SCALE OUTFLOW FROM A STAR-FORMING GALAXY ATz∼ 0.4

Abstract

We present a detailed analysis of a large-scale galactic outflow in the CGM of a massive (M h ∼ 10 12.5 M ⊙ ), star forming (∼ 6.9 M ⊙ yr −1 ), sub-L * (∼ 0.5L * 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 • ) 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, multicomponent structure with ultra-strong, wide velocity spread O VI (log N = 15.16 ± 0.04, ∆v 90 = 419 km s −1 ) and N V (log N = 14.69 ± 0.07, ∆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 (∼ 10 4 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 lowionization 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.

The Cosmic Evolution of the Metallicity Distribution of Ionized Gas Traced by Lyman Limit Systems

“…The breadth and strength of the O VI absorption in strong H I absorbers atz 2-3.5 are quite similar to those observed in starburst galaxies at low redshift (see, e.g., Grimes et al 2009;Tripp et al 2011;Muzahid et al 2015) Simcoe et al 2002;Muzahid et al 2012). This strongly suggests that the bulk of the strong and broad O VI associated with pLLSs and LLSs traces large-scale outflows from high-redshift starforming galaxies.…”

“…There is overlap between the low-and high-z surveys, but broad and strong O VI absorption associated with LLSs and pLLSs at < z 1 is the exception, not the norm. Only two strong H I absorbers with broad (  Dv 300 -km s 1 ) and strong O VI absorption at < z 1 have been reported so far, both associated with a massive, large-scale outflow from a massive star-forming galaxy (Tripp et al 2011;Fox et al 2013;Muzahid et al 2015). Therefore, randomly H Iselected pLLSs and LLSs at < z 1 and < < z 2.3 3.3 show a dramatic change not only in the MDF of their cool gas but also in the properties of the associated highly ionized gas.…”

On the covering fraction variability in an EUV mini-BAL outflow from PG 1206+459

“…In a standard thin-shell model, the kinetic luminosity of an outflow can be expressed asĖ k = 4πµmpCΩC f NHr d v 3 , where, mp is the proton mass, µ = 1.4 accounts for the mass of helium, and CΩ and C f are, respectively, the global and local covering fractions (see Appendix C of Muzahid et al 2015a). In M13 we have shown that 40 per cent of the intermediate redshift QSOs exhibit highly ionized outflows detected via the Ne VIII absorption.…”

Gas Accretion via Lyman Limit Systems

“…Indeed, only two absorbers not captured with these boundary limits shown in Fig. 6 are associated each with a massive, large-scale outflow from a massive star-forming galaxy (Tripp et al 2011;Muzahid et al 2015). These two absorbers at z < 1 have ∆ v 300 km s −1 and the metallicities of the highly ionized gas and cool ionized gas are similar and super-solar.…”

“…These two absorbers at z < 1 have ∆ v 300 km s −1 and the metallicities of the highly ionized gas and cool ionized gas are similar and super-solar. In the z < 1 sample, Fox et al (2013) also find that strong O VI absorption is not detected when the metallicity of cool gas is low; three of the four broadest and strongest systems at z < 1 happens to be three of the four most metal-rich pLLSs/LLSs in the sample, with similar properties (although not as extreme) to those of the absorbers associated with starburst galaxies (Tripp et al 2011;Muzahid et al 2015). My interpretation of the major difference in the frequency of strong and broad O VI between the low and high z pLLS/LLS surveys is that typically low-z galaxies are much more quiescent than their high redshift counterparts and, indeed, only in the comparatively rare lowz starburst galaxies can we find the extreme O VI absorption seen commonly at high z.…”