The CGM at Cosmic Noon with KCWI: Outflows from a Star-forming Galaxy at z = 2.071
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 Lyα emission from a 1.7L* galaxy at zgal = 2.0711 associated with a Lyman limit system with weak Mg II (Wr(2796) = 0.24 Å) in quasar field J143040+014939. The galaxy is star-forming (SFRFUV = 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 $[\mathrm{Si}/{\rm{H}}]=-{1.5}_{-0.3}^{+0.4}$ . The absorption system is roughly kinematically symmetric about zgal, 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 Vout = 109-588 km s-1 for half-opening angles of θ0 = 14°-75°. Assuming a constant Vout, it would take on average tout ∼ 111-597 Myr for the gas to reach 66 kpc. The outflow is energetic, with a mass outflow rate of ${\dot{M}}_{\mathrm{out}}\lt 52\pm 37$ 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2020
- DOI:
- 10.3847/1538-4357/abc561
- arXiv:
- arXiv:2002.08516
- Bibcode:
- 2020ApJ...904..164N
- Keywords:
-
- Lyman-alpha galaxies;
- High-redshift galaxies;
- Quasar absorption line spectroscopy;
- Galaxy evolution;
- Circumgalactic medium;
- 978;
- 734;
- 1317;
- 594;
- 1879;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 30 pages, 9 figures, 5 tables. Accepted for publication in ApJ on 26 October 2020