J/MNRAS/463/2997 Lockman Hole low-frequency radio sources (Mahony+, 2016)
The Lockman Hole project: LOFAR observations and spectral index properties of
low-frequency radio sources.
Mahony E.K., Morganti R., Prandoni I., Van Bemmel I.M., Shimwell T.W.,
Brienza M., Best P.N., Bruggen M., Calistro Rivera G., De Gasperin F.,
Hardcastle M.J., Harwood J.J., Heald G., Jarvis M.J., Mandal S.,
Miley G.K., Retana-montenegro E., Rottgering H.J.A., Sabater J., Tasse C.,
Van Velzen S., Van Weeren R.J., Williams W.L., White G.J.
<Mon. Not. R. Astron. Soc., 463, 2997-3020 (2016)>
=2016MNRAS.463.2997M 2016MNRAS.463.2997M (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Galaxies, radio ; Radio continuum
Keywords: surveys - galaxies: active - radio continuum: galaxies
Abstract:
The Lockman Hole is a well-studied extragalactic field with extensive
multi-band ancillary data covering a wide range in frequency,
essential for characterizing 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 18.6x14.7-arcsec and reaches an rms of
160µJy/beam 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
α1501400=-0.78±0.015. The median spectral index becomes
slightly flatter (increasing from α1501400=-0.84 to
α1501400=-0.75) with decreasing flux density down to S150
∼10mJy 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 150MHz. Using the deep,
multi-frequency data available in the Lockman Hole, we identify a
sample of 100 ultra-steep-spectrum sources and 13 peaked-spectrum
sources. We estimate that up to 21 per cent 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.
Description:
The Lockman Hole field (centred at RA=10:47:00.0, DE=+58:05:00 in
J2000 coordinates) was observed on 2013 March 18 for 10 h using the
LOFAR HBA array. A total of 36 stations were used in these
observations: 23 core and 13 remote stations.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 152 1302 Lockman-WSRT catalogue
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See also:
J/A+A/329/482 : ROSAT Deep Survey in the Lockman Hole (Hasinger+, 1998)
J/PASJ/53/445 : ASCA Deep survey in Lockman Hole Field (Ishisaki+, 2001)
J/A+A/398/901 : VLA survey at 6 cm in the Lockman Hole (Ciliegi+, 2003)
J/AJ/125/2521 : 2MASS6x survey of the Lockman Hole (Beichman+, 2003)
J/A+A/413/843 : Far IR survey in the Lockman Hole (Kawara+, 2004)
J/A+A/427/23 : 14.3um survey in the Lockman Hole (Fadda+, 2004)
J/A+A/427/773 : ISOCAM 14.3µm Deep Survey in Lockman Hole
(Rodighiero+, 2004)
J/A+A/444/79 : XMM observations of Lockman Hole brightest AGNs
(Mateos+, 2005)
J/A+A/473/105 : Lockman Hole AGN variability with XMM (Mateos+, 2007)
J/A+A/479/283 : XMM observations of the Lockman Hole (Brunner+, 2008)
J/A+A/487/475 : X-ray variability of AGNs in Lockman Hole (Papadakis+, 2008)
J/MNRAS/387/1037 : 610-MHz survey of Lockman Hole with GMRT (Garn+, 2008)
J/ApJS/185/433 : SWIRE/Chandra survey in Lockman Hole Field (Wilkes+, 2009)
J/A+A/514/A10 : AGNs in submm-selected Lockman Hole galaxies
(Serjeant+, 2010)
J/A+A/529/A135 : AGN Opt/IR properties in Lockman Hole (Rovilos+, 2011)
J/ApJS/198/1 : Photometry catalogs for the Lockman Hole (Fotopoulou+, 2012)
J/A+A/551/A97 : Lockman Hole/XMM VLBI observations (Middelberg+, 2013)
J/MNRAS/397/281 : Radio imaging in Lockman Hole (Ibar+, 2009)
J/MNRAS/462/2934 : Lockman Hole North 3GHz catalogue (Vernstrom+, 2016)
J/ApJ/856/67 : VLA 3GHz radio source catalog in Lockman Hole
(Cotton+, 2018)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Name LOFAR name (JHHMMSS+DDMMSS)
16- 17 I2 h RAh LOFAR 150MHz Right ascension (J2000)
19- 20 I2 min RAm LOFAR 150MHz Right ascension (J2000)
22- 25 F4.1 s RAs LOFAR 150MHz Right ascension (J2000)
27 A1 --- DE- LOFAR 150MHz Declination sign (J2000)
28- 29 I2 deg DEd LOFAR 150MHz Declination (J2000)
31- 32 I2 arcmin DEm LOFAR 150MHz Declination (J2000)
34- 37 F4.1 arcsec DEs LOFAR 150MHz Declination (J2000)
39- 44 F6.1 mJy St150 Integrated 150MHz flux density
46- 51 F6.2 mJy e_St150 rms uncertainty on St150
53- 56 F4.2 mJy rms Local rms
58 A1 --- Flag [SCM] Source flag (from pybdsm)
60- 77 A18 --- WSRT WSRT name (LHWJHHMMSS+DDMMSSA)
79- 80 I2 h RAWh ? WSRT Right ascension (J2000)
82- 83 I2 min RAWm ? WSRT Right ascension (J2000)
85- 89 F5.2 s RAWs ? WSRT Right ascension (J2000)
91 A1 --- DEW- WSRT Declination sign (J2000)
92- 93 I2 deg DEWd ? WSRT Declination (J2000)
95- 96 I2 arcmin DEWm ? WSRT Declination (J2000)
98-101 F4.1 arcsec DEWs ? WSRT Declination (J2000)
102 A1 --- l_Si1.4GHz Limit flag on Si1.4GHz
103-109 F7.3 mJy Si1.4GHz Integrated 1.4-GHz flux density
111-114 F4.2 mJy e_Si1.4GHz ? rms uncertainty on Si1.4GHz
116-120 F5.1 mJy Sp1.4GHz ? Peak 1.4-GHz flux density
122-125 F4.2 mJy e_Sp1.4GHz ? rms uncertainty on Sp1.4GHz
127-132 F6.2 arcsec maj ? Deconvolved 1.4-GHz source major axis (1)
134-138 F5.2 arcsec min ? Deconvolved 1.4-GHz source minor axis (1)
140-144 F5.1 deg PA []? Deconvolved 1.4-GHz source
position angle (1)
145 A1 --- l_SpIndex Limit flag on SpIndex
146-149 F4.1 --- SpIndex Spectral index between 150MHz and 1.4GHz,
α1400150
151-152 A2 --- FlagID Identification flag (2)
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Note (1): Objects listed with source sizes of 99.9 have been detected as two
separate components in the WSRT mosaic, but combined together and catalogued
as one object in post-processing.
Note (2): Identification flag as follows:
V = This match was identified and/or confirmed by visual inspection
(299 sources)
A = This match was automatically accepted (974 sources)
C = A complex match (16 sources). Likely to be a genuine match, but a
mismatch between the two source catalogues. For example, a double-lobed
radio galaxy may have been classified as a single source in the WSRT
catalogue, but catalogued as two separate components in the LOFAR
catalogue. These sources are included in the catalogue, but have been
excluded from further analysis.
L = A LOFAR source with no WSRT counterpart (six sources)
LC = ALOFARcomponent with noWSRT counterpart (seven sources)
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Acknowledgements:
Elizabeth Mahony, Elizabeth.Mahony(at)csiro.au
(End) Patricia Vannier [CDS] 23-May-2019