The Lockman Hole project: LOFAR observations and spectral index properties of low-frequency radio sources
The Lockman Hole is a well-studied extragalactic field with extensive multi-band ancillary data covering a wide range in frequency, essential for characterising the physical and evolutionary properties of the various source populations detected in deep radio fields (mainly star-forming galaxies and...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Journal article |
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Oxford University Press
2016
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| _version_ | 1826273419668226048 |
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| author | Mahony, E Morganti, R Prandoni, I Bemmel, I Shimwell, T Brienza, M Best, P Brüggen, M Rivera, G Gasperin, F Hardcastle, M Harwood, J Heald, G Jarvis, M Mandal, S Miley, G Retana-Montenegro, E Röttgering, H Sabater, J Tasse, C Velzen, S Weeren, R Williams, W White, G |
| author_facet | Mahony, E Morganti, R Prandoni, I Bemmel, I Shimwell, T Brienza, M Best, P Brüggen, M Rivera, G Gasperin, F Hardcastle, M Harwood, J Heald, G Jarvis, M Mandal, S Miley, G Retana-Montenegro, E Röttgering, H Sabater, J Tasse, C Velzen, S Weeren, R Williams, W White, G |
| author_sort | Mahony, E |
| collection | OXFORD |
| description | The Lockman Hole is a well-studied extragalactic field with extensive multi-band ancillary data covering a wide range in frequency, essential for characterising the physical and evolutionary properties of the various source populations detected in deep radio fields (mainly star-forming galaxies and AGNs). In this paper we present new 150-MHz observations carried out with the LOw Frequency ARray (LOFAR), allowing us to explore a new spectral window for the faint radio source population. This 150-MHz image covers an area of 34.7 square degrees with a resolution of 18.6$\times$14.7 arcsec and reaches an rms of 160 $\mu$Jy beam$^{-1}$ at the centre of the field. As expected for a low-frequency selected sample, the vast majority of sources exhibit steep spectra, with a median spectral index of $\alpha_{150}^{1400}=-0.78\pm0.015$. The median spectral index becomes slightly flatter (increasing from $\alpha_{150}^{1400}=-0.84$ to $\alpha_{150}^{1400}=-0.75$) with decreasing flux density down to $S_{150} \sim$10 mJy before flattening out and remaining constant below this flux level. For a bright subset of the 150-MHz selected sample we can trace the spectral properties down to lower frequencies using 60-MHz LOFAR observations, finding tentative evidence for sources to become flatter in spectrum between 60 and 150 MHz. Using the deep, multi-frequency data available in the Lockman Hole, we identify a sample of 100 Ultra-steep spectrum (USS) sources and 13 peaked spectrum sources. We estimate that up to 21 percent of these could have $z>4$ and are candidate high-$z$ radio galaxies, but further follow-up observations are required to confirm the physical nature of these objects. |
| first_indexed | 2024-03-06T22:27:54Z |
| format | Journal article |
| id | oxford-uuid:57474cd0-12b2-4500-8fe1-1b379cc96726 |
| institution | University of Oxford |
| last_indexed | 2024-03-06T22:27:54Z |
| publishDate | 2016 |
| publisher | Oxford University Press |
| record_format | dspace |
| spelling | oxford-uuid:57474cd0-12b2-4500-8fe1-1b379cc967262022-03-26T16:55:46ZThe Lockman Hole project: LOFAR observations and spectral index properties of low-frequency radio sourcesJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:57474cd0-12b2-4500-8fe1-1b379cc96726Symplectic Elements at OxfordOxford University Press2016Mahony, EMorganti, RPrandoni, IBemmel, IShimwell, TBrienza, MBest, PBrüggen, MRivera, GGasperin, FHardcastle, MHarwood, JHeald, GJarvis, MMandal, SMiley, GRetana-Montenegro, ERöttgering, HSabater, JTasse, CVelzen, SWeeren, RWilliams, WWhite, GThe Lockman Hole is a well-studied extragalactic field with extensive multi-band ancillary data covering a wide range in frequency, essential for characterising the physical and evolutionary properties of the various source populations detected in deep radio fields (mainly star-forming galaxies and AGNs). In this paper we present new 150-MHz observations carried out with the LOw Frequency ARray (LOFAR), allowing us to explore a new spectral window for the faint radio source population. This 150-MHz image covers an area of 34.7 square degrees with a resolution of 18.6$\times$14.7 arcsec and reaches an rms of 160 $\mu$Jy beam$^{-1}$ at the centre of the field. As expected for a low-frequency selected sample, the vast majority of sources exhibit steep spectra, with a median spectral index of $\alpha_{150}^{1400}=-0.78\pm0.015$. The median spectral index becomes slightly flatter (increasing from $\alpha_{150}^{1400}=-0.84$ to $\alpha_{150}^{1400}=-0.75$) with decreasing flux density down to $S_{150} \sim$10 mJy before flattening out and remaining constant below this flux level. For a bright subset of the 150-MHz selected sample we can trace the spectral properties down to lower frequencies using 60-MHz LOFAR observations, finding tentative evidence for sources to become flatter in spectrum between 60 and 150 MHz. Using the deep, multi-frequency data available in the Lockman Hole, we identify a sample of 100 Ultra-steep spectrum (USS) sources and 13 peaked spectrum sources. We estimate that up to 21 percent of these could have $z>4$ and are candidate high-$z$ radio galaxies, but further follow-up observations are required to confirm the physical nature of these objects. |
| spellingShingle | Mahony, E Morganti, R Prandoni, I Bemmel, I Shimwell, T Brienza, M Best, P Brüggen, M Rivera, G Gasperin, F Hardcastle, M Harwood, J Heald, G Jarvis, M Mandal, S Miley, G Retana-Montenegro, E Röttgering, H Sabater, J Tasse, C Velzen, S Weeren, R Williams, W White, G The Lockman Hole project: LOFAR observations and spectral index properties of low-frequency radio sources |
| title | The Lockman Hole project: LOFAR observations and spectral index
properties of low-frequency radio sources |
| title_full | The Lockman Hole project: LOFAR observations and spectral index
properties of low-frequency radio sources |
| title_fullStr | The Lockman Hole project: LOFAR observations and spectral index
properties of low-frequency radio sources |
| title_full_unstemmed | The Lockman Hole project: LOFAR observations and spectral index
properties of low-frequency radio sources |
| title_short | The Lockman Hole project: LOFAR observations and spectral index
properties of low-frequency radio sources |
| title_sort | lockman hole project lofar observations and spectral index properties of low frequency radio sources |
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