Ionized Gas Extended Over 40 kpc in an Odd Radio Circle Host Galaxy

Alison L. Coil; Serena Perrotta; David S. N. Rupke; Cassandra Lochhaas; Christy A. Tremonti; Aleks Diamond-Stanic; Drummond Fielding; James Geach; Ryan C. Hickox; John Moustakas; Gregory H. Rudnick; Paul Sell; Kelly E. Whalen

arXiv · 2310.15162

Ionized Gas Extended Over 40 kpc in an Odd Radio Circle Host Galaxy

Alison L. Coil·Serena Perrotta·David S. N. Rupke·Cassandra Lochhaas·Christy A. Tremonti·Aleks Diamond-Stanic·Drummond Fielding·James Geach·Ryan C. Hickox·John Moustakas·Gregory H. Rudnick·Paul Sell·Kelly E. Whalen

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Abstract

A new class of extragalactic astronomical sources discovered in 2021, named Odd Radio Circles (ORCs, Norris et al. 2021), are large rings of faint, diffuse radio continuum emission spanning ~1 arcminute on the sky. Galaxies at the centers of several ORCs have photometric redshifts of z~0.3-0.6, implying physical scales of several 100 kiloparsecs in diameter for the radio emission, the origin of which is unknown. Here we report spectroscopic data on an ORC including strong [OII] emission tracing ionized gas in the central galaxy of ORC4 at z=0.4512. The physical extent of the [OII] emission is ~40 kpc in diameter, larger than expected for a typical early-type galaxy (Pandya et al, 2017) but an order of magnitude smaller than the large-scale radio continuum emission. We detect a ~200 km/s velocity gradient across the [OII] nebula, as well as a high velocity dispersion of ~180 km/s. The [OII] equivalent width (EW, ~50 Ang) is extremely high for a quiescent galaxy. The morphology, kinematics, and strength of the [OII] emission are consistent with the infall of shock ionized gas near the galaxy, following a larger-scale, outward moving shock driven by a galactic wind. Both the extended optical and radio emission, while observed on very different scales, may therefore result from the same dramatic event.

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Alison L. Coil, Serena Perrotta, David S. N. Rupke, Cassandra Lochhaas, Christy A. Tremonti, Aleks Diamond-Stanic, Drummond Fielding, James Geach, Ryan C. Hickox, John Moustakas, Gregory H. Rudnick, Paul Sell, Kelly E. Whalen. 2023-10-23. Ionized Gas Extended Over 40 kpc in an Odd Radio Circle Host Galaxy. https://arxiv.org/abs/2310.15162

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