Oral Presentation

Ionized Gas in an Odd Radio Circle (Remote)

Author(s): Alison Coil (University of California San Diego)

Presenter: Alison Coil (University of California San Diego)

A new class of extragalactic sources was discovered in 2021, named Odd Radio Circles (ORCs). ORCs are rings of faint, diffuse radio continuum emission spanning ~1 arcminute on the sky. The photometric redshifts of galaxies detected at their centers imply physical scales of the radio emission of several 100 kiloparsecs. I will present the first spectroscopic data on an ORC, including detection of spatially-extended optical emission lines. Keck Cosmic Web Imager (KCWI) data reveal strong [O II] emission tracing ionized gas in ORC4 at z = 0.4512. The [O II] emission is ~40 kpc in diameter, very large for a typical early-type galaxy but an order of magnitude smaller than the radio continuum emission. The [O II] nebula has a high velocity dispersion and an extremely high equivalent width. The morphology, kinematics, and strength of the [O II] emission are consistent with the ionized gas arising from shocks near the galaxy associated with the subsequent infall of material resulting from a larger-scale forward-moving shock, such that both the extended optical and radio emission, while on very different scales, result from the same dramatic event. These data support ORCs being large-scale shocks driven from an outflowing galactic wind.