Finding Quasars behind the Galactic Plane. II. Spectroscopic Identifications of 204 Quasars at $|b|< 20\deg$

TL;DR

This study reports the discovery and spectroscopic confirmation of 204 quasars behind the Galactic plane, expanding the known sample and providing valuable data for astrometric and astrophysical research despite observational challenges.

Contribution

The paper presents a large, new sample of 204 spectroscopically confirmed GPQs, including 191 new discoveries, with detailed spectral analysis and black hole mass estimates, demonstrating effective selection methods.

Findings

204 GPQs confirmed spectroscopically, 191 are new discoveries.

GPQs have higher black hole masses and luminosities than SDSS DR7 quasars.

The selection method achieves at least 85.2% purity in quasar identification.

Abstract

Quasars behind the Galactic plane (GPQs) are important astrometric references and valuable probes of Galactic gas, yet the search for GPQs is difficult due to severe extinction and source crowding in the Galactic plane. In this paper, we present a sample of 204 spectroscopically confirmed GPQs at |b|<20{\deg}, 191 of which are new discoveries. This GPQ sample covers a wide redshift range from 0.069 to 4.487. For the subset of 230 observed GPQ candidates, the lower limit of the purity of quasars is 85.2%, and the lower limit of the fraction of stellar contaminants is 6.1%. Using a multicomponent spectral fitting, we measure the emission line and continuum flux of the GPQs, and estimate their single-epoch virial black hole masses. Due to selection effects raised from Galactic extinction and target magnitude, these GPQs have higher black hole masses and continuum luminosities in comparison to the SDSS DR7 quasar sample. The spectral-fitting results and black hole mass estimates are compiled into a main spectral catalog, and an extended spectral catalog of GPQs. The successful identifications prove the reliability of both our GPQ selection methods and the GPQ candidate catalog, shedding light on the astrometric and astrophysical programs that make use of a large sample of GPQs in the future.