Dawn Erb - Mapping the circumgalactic medium

Abstract: Lya photons are resonantly scattered by neutral hydrogen, and may therefore trace both the spatial extent and the kinematics of the gas surrounding galaxies. I will present observations of the extended Lya halo of a low mass, low metallicity star-forming galaxy at z=2.3. Using the Keck Cosmic Web Imager (KCWI), the blue-sensitive optical integral field spectrograph recently installed on the Keck II telescope, we detect Lya in emission to a radius of 23 kpc, study the double-peaked spectroscopic Lya profile in individual spectral pixels over a ∼25×30 kpc region, finding significant variations in the peak ratio and peak separation. The data are consistent with a model in which the galaxy is surrounded by a roughly spherical outflow, with significant variations in the column density, covering fraction, or velocity range of the gas. I will conclude with a brief discussion of future prospects for similar observations.