The Morphology and Kinematics of a Giant, Symmetric Nebula Around a Radio-Loud Quasar 3C57: Extended Rotating Gas or Biconical Outflows?

Abstract

Gas flows between galaxies and the CGM play a crucial role in galaxy evolution. When ionized by a quasar, these gas flows can be directly traced as giant nebulae. We present a study of a giant nebula around a radio-loud quasar, 3C57 at $z\approx 0.672$. Observations from MUSE reveal that the nebula is elongated with a major axis of $70\mathrm{kpc}$ and a minor axis of $40\mathrm{kpc}$. The nebula displays an approximately symmetric blueshifted-redshifted pattern along the major axis and multi-component emission features in its $[\mathrm{O}\mathrm{II}]$ and $[\mathrm{O}\mathrm{III}]$ profiles. The morphology and kinematics can be explained as rotating gas or biconical outflow, both of which qualitatively reproduce the observed position-velocity diagram. The 3C57 nebula is significantly more kinematically disturbed, with ${\mathrm{W}}_{80}$ (the line width encompassing 80$\%$ of the flux) of approximately $300-400\mathrm{km}{\mathrm{s}}^{-1}$, compared to $\mathrm{H}\mathrm{I}$ gas in local early-type galaxies, which typically shows ${\mathrm{W}}_{80}\approx 50\mathrm{km}{\mathrm{s}}^{-1}$. This velocity dispersion is comparable to the gas in cool-core clusters despite originating in a group 100 times less massive. For biconical outflow models, the inferred $10-20^{\circ }$ inclination angle is in tension with the unobscured nature of the quasar, as the dusty torus is expected to be perpendicular to the outflow. Neither a quiescent rotating gas origin nor a biconical outflow fully reproduces the observed kinematics and morphology of the 3C57 nebula, suggesting a more intricate origin likely involving both rotation and AGN feedback.

13 pages, 4 figures; Accepted by ApJ