SIMBAD references

2017MNRAS.467.2039C - Mon. Not. R. Astron. Soc., 467, 2039-2060 (2017/May-2)

Radio spectra of bright compact sources at z > 4.5.

COPPEJANS R., VAN VELZEN S., INTEMA H.T., MUELLER C., FREY S., COPPEJANS D.L., CSEH D., WILLIAMS W.L., FALCKE H., KORDING E.G., ORRU E., PARAGI Z. and GABANYI K.E.

Abstract (from CDS):

High-redshift quasars are important to study galaxy and active galactic nuclei evolution, test cosmological models and study supermassive black hole growth. Optical searches for high-redshift sources have been very successful, but radio searches are not hampered by dust obscuration and should be more effective at finding sources at even higher redshifts. Identifying high-redshift sources based on radio data is, however, not trivial. Here we report on new multifrequency Giant Metrewave Radio Telescope observations of eight z > 4.5 sources previously studied at high angular resolution with very long baseline interferometry (VLBI). Combining these observations with those from the literature, we construct broad-band radio spectra of all 30 z > 4.5 sources that have been observed with VLBI. In the sample we found flat, steep and peaked spectra in approximately equal proportions. Despite several selection effects, we conclude that the z > 4.5 VLBI (and likely also non-VLBI) sources have diverse spectra and that only about a quarter of the sources in the sample have flat spectra. Previously, the majority of high-redshift radio sources were identified based on their ultrasteep spectra. Recently, a new method has been proposed to identify these objects based on their megahertz-peaked spectra. No method would have identified more than 18 per cent of the high-redshift sources in this sample. More effective methods are necessary to reliably identify complete samples of high-redshift sources based on radio data.

Abstract Copyright: © 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society

Journal keyword(s): galaxies: active - galaxies: high-redshift - radio continuum: galaxies - radio continuum: galaxies

Simbad objects: 38

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