# Optical Spectra of Candidate International Celestial Reference Frame (ICRF) Flat-Spectrum Radio Sources. III

## TL;DR

This study provides spectroscopic data and redshift measurements for 160 flat-spectrum radio sources from the ICRF catalog, enhancing the understanding of their optical properties and classifications.

## Contribution

The paper reports new spectroscopic observations and redshift determinations for ICRF radio sources, including the classification of some as BL Lac objects, using multiple large telescopes.

## Key findings

- Redshifts determined for 112 quasars and radio galaxies.
- Identification of 14 BL Lac objects with featureless spectra.
- Spectroscopic data obtained from three major telescopes.

## Abstract

In extending our spectroscopic program, which targets sources drawn from the International Celestial Reference Frame (ICRF) Catalog, we have obtained spectra for about 160 compact flat-spectrum radio sources and determined redshifts for 112 quasars and radio galaxies. A further 14 sources with featureless spectra have been classified as BL Lac objects. Spectra were obtained at three telescopes: the 3.58-m ESO New Technology Telescope (NTT), and the two 8.2-m Gemini telescopes in Hawaii and Chile. While most of the sources are powerful quasars, a significant fraction of radio galaxies is also included from the list of non-defining ICRF radio sources.