Gaia-supported re-discovery of a remarkable weak line quasar from a variability and proper motion survey

TL;DR

This paper uses Gaia data and new spectra to re-identify VPMS J170850.95+433223.7 as a weak line quasar at z=2.345, revealing its properties, high accretion rate, and possible high-velocity outflows.

Contribution

It demonstrates the re-discovery and detailed characterization of a weak line quasar using Gaia data combined with new spectral observations.

Findings

Confirmed as a WLQ at z=2.345 with faint emission lines

Estimated supermassive black hole mass of ~10^9 M_sun

Identified high-velocity outflows possibly linked to high accretion

Abstract

We demonstrate that VPMS J170850.95+433223.7 is a weak line quasar (WLQ) which is remarkable in several respects. It was already classified as a probable quasar two decades ago, but with considerable uncertainty. The non-significant proper motion and parallax from the Gaia early data release 3 have solidified this assumption. Based on previously unpublished spectra, we show that VPMS J170850.95+433223.7 is a WLQ at z = 2.345 with immeasurably faint broad emission lines in the rest-frame ultraviolet. A preliminary estimate suggests that it hosts a supermassive black hole of ~10^9 M_sun accreting close to the Eddington limit, perhaps at the super-Eddington level. We identify two absorber systems with blueward velocity offsets of 0.05c and 0.1c, which could represent high-velocity outflows, which are perhaps related to the high accretion state of the quasar.