The first comprehensive study of a giant nebula around a radio-quiet quasar in the $z<1$ Universe

Abstract

We present the first comprehensive study of a giant, $\approx 70$ kpc-scale nebula around a radio-quiet quasar at $z<1$. The analysis is based on deep integral field spectroscopy with MUSE of the field of HE0238$-$1904, a luminous quasar at $z=0.6282$. The nebula emits strongly in $[\mathrm{O}\mathrm{II}]$, $\mathrm{H}\beta$, and $[\mathrm{O}\mathrm{III}]$, and the quasar resides in an unusually overdense environment for a radio-quiet system. The environment likely consists of two groups which may be merging, and in total have an estimated dynamical mass of $M_{\mathrm{dyn}}\approx 4\times 10^{13}$ to $10^{14}{\mathrm{M}}_{\odot }$. The nebula exhibits largely quiescent kinematics and irregular morphology. The nebula may arise primarily through interaction-related stripping of circumgalactic and interstellar medium (CGM/ISM) of group members, with some potential contributions from quasar outflows. The simultaneous presence of the giant nebula and a radio-quiet quasar in a rich environment suggests a correlation between such circum-quasar nebulae and environmental effects. This possibility can be tested with larger samples. The upper limits on the electron number density implied by the $[\mathrm{O}\mathrm{II}]$ doublet ratio range from $\log (n_{\mathrm{e},[\mathrm{O}\mathrm{II}]}/\mathrm{c}{\mathrm{m}}^{-3})<1.2$ to $2.8$. However, assuming a constant quasar luminosity and negligible projection effects, the densities implied from the measured line ratios between different ions (e.g., $[\mathrm{O}\mathrm{II}]$, $[\mathrm{O}\mathrm{III}]$, and $[\mathrm{Ne}\mathrm{V}]$) and photoionization simulations are often $10-400$ times larger. This large discrepancy can be explained by quasar variability on a timescale of $\approx 10^4-10^5$ years.

19 pages, 9 figures, 3 tables; Accepted by MNRAS