Radio spectra of bright compact sources at z > 4.5
MetadataShow full item record
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 newmultifrequency Giant MetrewaveRadio 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 megahertzpeaked 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.
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Showing items related by title, author, creator and subject.
Middelberg, E.; Norris, R.; Hales, C.; Seymour, Nick; Johnston-Hollitt, M.; Huynh, M.; Lenc, E.; Mao, M. (2010)Context. Infrared-faint radio sources (IFRS) are objects that have flux densities of several mJy at 1.4GHz, but that are invisible at 3.6µm when using sensitive Spitzer observations with µJy sensitivities. Their nature ...
Coppejans, R.; Cseh, D.; van Velzen, S.; Falcke, H.; Intema, Hubertus; Paragi, Z.; Müller, C.; Williams, W.; Frey, S.; Gurvits, L.; Körding, E. (2016)Megahertz peaked-spectrum (MPS) sources have spectra that peak at frequencies below 1 GHz in the observer's frame and are believed to be radio-loud active galactic nuclei (AGN). We recently presented a new method to search ...
Ultra steep spectrum radio sources in the lockman hole: Servs identifications and redshift distribution at the faintest radio fluXESAfonso, J.; Bizzocchi, L.; Ibar, E.; Grossi, M.; Simpson, C.; Chapman, S.; Jarvis, M.; Rottgering, H.; Norris, R.; Dunlop, J.; Ivison, R.; Messias, H.; Pforr, J.; Vaccari, M.; Seymour, Nick; Best, P.; Gonzlez-Solares, E.; Farrah, D.; Fernandes, C.; Huang, J.; Lacy, M.; Maraston, C.; Marchetti, L.; Mauduit, J.; Oliver, S.; Rigopoulou, D.; Stanford, S.; Surace, J.; Zeimann, G. (2011)Ultra steep spectrum (USS) radio sources have been successfully used to select powerful radio sources at high redshifts (z ~>2). Typically restricted to large-sky surveys and relatively bright radio flux densities, it has ...