Optical Spectra of Candidate Southern Hemisphere International Celestial Reference Frame (ICRF) radio sources

TL;DR

This study provides optical spectra and redshift measurements for 38 southern hemisphere radio sources, enhancing the celestial reference frame and aiding in understanding source motions through spectroscopic and VLBI data.

Contribution

It offers new spectroscopic data for southern ICRF candidate sources, including redshifts and classifications, improving the celestial reference frame.

Findings

Redshifts obtained for 30 quasars and one radio galaxy.

Identification of 7 probable BL Lac objects.

Addition of data for sources with redshift > 2 to refine proper motion distribution.

Abstract

We present the results of spectroscopic observations of the optical counterparts of 47 southern radio sources from the candidate International Celestial Reference Catalogue (ICRC), as part of a Very Long Baseline Interferometry (VLBI) program to strengthen the celestial reference frame, especially in the south. The observations were made with the 3.58-meter European Southern Observatory New Technology Telescope (NTT). We obtained redshifts for 30 quasars and one radio galaxy, with a further 7 objects being probable BL Lac objects with featureless spectra. Of the remainder, four were clear misidentifications with Galactic stars and five had low signal-to-noise spectra and could not be classified. These results, in combination with new VLBI data of the radio sources with redshifts more than 2, add significantly to the existing data needed to refine the distribution of source proper motions over the celestial sphere.