Understanding the Nature of an Unusual Post-Starburst Quasar with Exceptionally Strong Ne V Emission

TL;DR

This study investigates a unique high-redshift quasar with strong high-ionization emission lines, revealing its outflow properties, star formation history, and dust characteristics, suggesting it is a young, rapidly evolving AGN in a transitional phase.

Contribution

It provides the first detailed analysis of a rare post-starburst quasar with extreme Ne V emission, linking outflow dynamics, star formation history, and dust properties in a young AGN.

Findings

The quasar exhibits high-velocity outflows of 4000 km/s.

It experienced a starburst 400 Myr ago that was subsequently quenched.

The strong extinction is due to AGN activity, not the host galaxy.

Abstract

We present a $z = 0.94$ quasar, SDSS J004846.45-004611.9, discovered in the SDSS-III BOSS survey. A visual analysis of this spectrum reveals highly broadened and blueshifted narrow emission lines, in particular [Ne~V]$\lambda3426$ and [O~III]$\lambda5007$, with outflow velocities of 4000 km s$^{-1}$, along with unusually large [Ne V]$\lambda3426$/[Ne III]$\lambda3869$ ratios. The gas shows higher ionization at higher outflow velocities, indicating a connection between the powerful outflow and the unusual strength of the high ionization lines. The SED and the $i - \text{W3}$ color of the source reveal that it is likely a "core" Extremely Red Quasar (core ERQ); a candidate population of young AGN that are violently "blowing out" gas and dust from their centers. The dominance of host galaxy light in its spectrum and its fortuitous position in the SDSS S82 region allows us to measure its star formation history and investigate for variability for the first time in an ERQ. Our analysis indicates that SDSS J004846.45-004611.9 underwent a short-lived starburst phase 400 Myr ago and was subsequently quenched, possibly indicating a time-lag between star formation quenching and the onset of AGN activity. We also find that the strong extinction can be uniquely attributed to the AGN and does not persist in the host galaxy, contradicting a scenario where the source has recently transitioned from being a dusty sub-mm galaxy. In our relatively shallow photometric data, the source does not appear to be variable at $0.24-2.4~\mu$m in the restframe, most likely due to the dominant contribution of host galaxy starlight at these wavelengths.