The spectroscopic follow-up of the QUBRICS bright quasar survey

TL;DR

This paper reports on the spectroscopic follow-up of the QUBRICS survey, which identified 224 bright quasars at various redshifts using machine learning, enabling future cosmological studies like redshift drift measurements.

Contribution

The paper presents the current status and results of the QUBRICS survey, including the identification of new high-redshift quasars and an assessment of the selection method’s success rate.

Findings

Identified 55 new high-redshift, bright QSOs.

Total of 224 bright QSOs at z<=2.5 identified.

Selection success rate estimated at 68%.

Abstract

We present the results of the spectroscopic follow up of the QUBRICS survey. The selection method is based on a machine learning approach applied to photometric catalogs, covering an area of $\sim$ 12,400 deg$^2$ in the Southern Hemisphere. The spectroscopic observations started in 2018 and identified 55 new, high-redshift (z>=2.5), bright (i<=18) QSOs, with the catalog published in late 2019. Here we report the current status of the survey, bringing the total number of bright QSOs at z<=2.5 identified by QUBRICS to 224. The success rate of the QUBRICS selection method, in its most recent training, is estimated to be 68%. The predominant contaminant turns out to be lower-z QSOs at z<2.5. This survey provides a unique sample of bright QSOs at high-z available for a number of cosmological investigations. In particular, carrying out the redshift drift measurements (Sandage Test) in the Southern Hemisphere, using the HIRES spectrograph at the 39m ELT, appears to be possible with less than 2500 hours of observations spread over 30 targets in 25 years.