The CGM at Cosmic Noon with KCWI: Outflows from a Star-forming Galaxy at z = 2.071
Nikole M. Nielsen, Glenn G. Kacprzak, Stephanie K. Pointon, M. T. Murphy, Christopher W. Churchill, Romeel Davé
Abstract
Abstract We present the first results from our “CGM at Cosmic Noon with KCWI” program to study gas flows in the circumgalactic medium (CGM) at z = 2–3. Combining the power of a high-resolution VLT/UVES quasar spectrum, a Hubble Space Telescope/Advanced Camera for Surveys image, and integral field spectroscopy with Keck/KCWI (Keck Cosmic Web Imager), we detected Ly α emission from a 1.7 L * galaxy at z gal = 2.0711 associated with a Lyman limit system with weak Mg ii ( W r (2796) = 0.24 Å) in quasar field J143040+014939. The galaxy is star-forming (SFR FUV = 37.8 M ⊙ yr −1 ) and clumpy: either an edge-on disk ( i = 85°) or, less likely, a major merger. The background quasar probes the galaxy at an impact parameter of D = 66 kpc along the projected galaxy minor axis (Φ = 89°). From photoionization modeling of the absorption system, we infer a total line-of-sight CGM metallicity of . The absorption system is roughly kinematically symmetric about z gal , with a full Mg ii velocity spread of ∼210 km s −1 . Given the galaxy–quasar orientation, CGM metallicity, and gas kinematics, we interpret this gas as an outflow that has likely swept up additional material. By modeling the absorption as a polar outflow cone, we find the gas is decelerating with average radial velocity V out = 109–588 km s −1 for half-opening angles of θ 0 = 14°–75°. Assuming a constant V out , it would take on average t out ∼ 111–597 Myr for the gas to reach 66 kpc. The outflow is energetic, with a mass outflow rate of M ⊙ yr −1 and mass loading factor of η < 1.4 ± 1.0. We aim to build a sample of ∼50 Mg ii absorber–galaxy pairs at this epoch to better understand gas flows when they are most actively building galaxies.