# University of Hertfordshire

## The Lockman Hole project: LOFAR observations and spectral index properties of low-frequency radio sources

Research output: Contribution to journalArticle

### Standard

The Lockman Hole project : LOFAR observations and spectral index properties of low-frequency radio sources. / Mahony, E. K.; Morganti, R.; Prandoni, I.; Bemmel, I. M. van; Shimwell, T. W.; Brienza, M.; Best, P. N.; Brüggen, M.; Rivera, G. Calistro; Gasperin, F. de; Hardcastle, M. J.; Harwood, J. J.; Heald, G.; Jarvis, M. J.; Mandal, S.; Miley, G. K.; Retana-Montenegro, E.; Röttgering, H. J. A.; Sabater, J.; Tasse, C.; Velzen, S. van; Weeren, R. J. van; Williams, W. L.; White, G. J.

In: Monthly Notices of the Royal Astronomical Society, Vol. 463, No. 3, 11.12.2016, p. 2297-3020.

Research output: Contribution to journalArticle

### Harvard

Mahony, EK, Morganti, R, Prandoni, I, Bemmel, IMV, Shimwell, TW, Brienza, M, Best, PN, Brüggen, M, Rivera, GC, Gasperin, FD, Hardcastle, MJ, Harwood, JJ, Heald, G, Jarvis, MJ, Mandal, S, Miley, GK, Retana-Montenegro, E, Röttgering, HJA, Sabater, J, Tasse, C, Velzen, SV, Weeren, RJV, Williams, WL & White, GJ 2016, 'The Lockman Hole project: LOFAR observations and spectral index properties of low-frequency radio sources', Monthly Notices of the Royal Astronomical Society, vol. 463, no. 3, pp. 2297-3020. https://doi.org/10.1093/mnras/stw2225

### APA

Mahony, E. K., Morganti, R., Prandoni, I., Bemmel, I. M. V., Shimwell, T. W., Brienza, M., ... White, G. J. (2016). The Lockman Hole project: LOFAR observations and spectral index properties of low-frequency radio sources. Monthly Notices of the Royal Astronomical Society, 463(3), 2297-3020. https://doi.org/10.1093/mnras/stw2225

### Author

Mahony, E. K. ; Morganti, R. ; Prandoni, I. ; Bemmel, I. M. van ; Shimwell, T. W. ; Brienza, M. ; Best, P. N. ; Brüggen, M. ; Rivera, G. Calistro ; Gasperin, F. de ; Hardcastle, M. J. ; Harwood, J. J. ; Heald, G. ; Jarvis, M. J. ; Mandal, S. ; Miley, G. K. ; Retana-Montenegro, E. ; Röttgering, H. J. A. ; Sabater, J. ; Tasse, C. ; Velzen, S. van ; Weeren, R. J. van ; Williams, W. L. ; White, G. J. / The Lockman Hole project : LOFAR observations and spectral index properties of low-frequency radio sources. In: Monthly Notices of the Royal Astronomical Society. 2016 ; Vol. 463, No. 3. pp. 2297-3020.

### Bibtex

title = "The Lockman Hole project: LOFAR observations and spectral index properties of low-frequency radio sources",
abstract = "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.",
keywords = "astro-ph.GA, astro-ph.CO",
author = "Mahony, {E. K.} and R. Morganti and I. Prandoni and Bemmel, {I. M. van} and Shimwell, {T. W.} and M. Brienza and Best, {P. N.} and M. Br{\"u}ggen and Rivera, {G. Calistro} and Gasperin, {F. de} and Hardcastle, {M. J.} and Harwood, {J. J.} and G. Heald and Jarvis, {M. J.} and S. Mandal and Miley, {G. K.} and E. Retana-Montenegro and R{\"o}ttgering, {H. J. A.} and J. Sabater and C. Tasse and Velzen, {S. van} and Weeren, {R. J. van} and Williams, {W. L.} and White, {G. J.}",
note = "E. K. Mahoy, et al., 'The Lockman Hole project: LOFAR observations and spectral index properties of low-frequency radio sources' , the version of record [MNRAS (December 11, 2016) Vol 463 (3): 2997-3020, first published on line September 5, 2016, is available on line at doi: 10.1093/mnras/stw2225 Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.",
year = "2016",
month = "12",
day = "11",
doi = "10.1093/mnras/stw2225",
language = "English",
volume = "463",
pages = "2297--3020",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",
number = "3",

}

### RIS

TY - JOUR

T1 - The Lockman Hole project

T2 - LOFAR observations and spectral index properties of low-frequency radio sources

AU - Mahony, E. K.

AU - Morganti, R.

AU - Prandoni, I.

AU - Bemmel, I. M. van

AU - Shimwell, T. W.

AU - Brienza, M.

AU - Best, P. N.

AU - Brüggen, M.

AU - Rivera, G. Calistro

AU - Gasperin, F. de

AU - Hardcastle, M. J.

AU - Harwood, J. J.

AU - Heald, G.

AU - Jarvis, M. J.

AU - Mandal, S.

AU - Miley, G. K.

AU - Retana-Montenegro, E.

AU - Röttgering, H. J. A.

AU - Sabater, J.

AU - Tasse, C.

AU - Velzen, S. van

AU - Weeren, R. J. van

AU - Williams, W. L.

AU - White, G. J.

N1 - E. K. Mahoy, et al., 'The Lockman Hole project: LOFAR observations and spectral index properties of low-frequency radio sources' , the version of record [MNRAS (December 11, 2016) Vol 463 (3): 2997-3020, first published on line September 5, 2016, is available on line at doi: 10.1093/mnras/stw2225 Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

PY - 2016/12/11

Y1 - 2016/12/11

N2 - 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.

AB - 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.

KW - astro-ph.GA

KW - astro-ph.CO

U2 - 10.1093/mnras/stw2225

DO - 10.1093/mnras/stw2225

M3 - Article

VL - 463

SP - 2297

EP - 3020

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 3

ER -