Radio spectra of bright compact sources at z>4.5
High-redshift quasars are important to study galaxy and active galactic nuclei (AGN) 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 multi-frequency Giant Metrewave Radio Telescope (GMRT) 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 ultra-steep spectra (USS). Recently a new method has been proposed to identify these objects based on their megahertz-peaked spectra (MPS). Neither method would have identified more than 18% 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.
Item Type | Article |
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Uncontrolled Keywords | galaxies: active; galaxies: high-redshift; radio continuum: galaxies |
Date Deposited | 26 Jul 2024 20:16 |
Last Modified | 26 Jul 2024 20:16 |
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Read more research from the creator(s):
- Coppejans, Rocco
- Velzen, Sjoert van
- Intema, Huib T.
- Müller, Cornelia
- Frey, Sándor
- Coppejans, Deanne L.
- Cseh, Dávid
- Williams, Wendy
- Falcke, Heino
- Körding, Elmar G.
- Orrú, Emanuela
- Paragi, Zsolt
- Gabányi, Krisztina É.
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- https://arxiv.org/pdf/1701.06622.pdf [error in script]