J/ApJ/793/82 LOFAR Bootes and 3C295 field sources (van Weeren+, 2014)
LOFAR low-band antenna observations of the 3C 295 and Bootes fields: source
counts and ultra-steep spectrum sources.
van Weeren R.J., Williams W.L., Tasse C., Rottgering H.J.A., Rafferty D.A.,
van der Tol S., Heald G., White G.J., Shulevski A., Best P., Intema H.T.,
Bhatnagar S., Reich W., Steinmetz M., van Velzen S., Ensslin T.A.,
Prandoni I., de Gasperin F., Jamrozy M., Brunetti G., Jarvis M.J.,
McKean J.P., Wise M.W., Ferrari C., Harwood J., Oonk J.B.R., Hoeft M.,
Kunert-Bajraszewska M., Horellou C., Wucknitz O., Bonafede A., Mohan N.R.,
Scaife A.M.M., Klockner H.-R., van Bemmel I.M., Merloni A., Chyzy K.T.,
Engels D., Falcke H., Pandey-Pommier M., Alexov A., Anderson J.,
Avruch I.M., Beck R., Bell M.E., Bentum M.J., Bernardi G., Breitling F.,
Broderick J., Brouw W.N., Bruggen M., Butcher H.R., Ciardi B., de Geus E.,
de Vos M., Deller A., Duscha S., Eisloffel J., Fallows R.A., Frieswijk W.,
Garrett M.A., Griessmeier J., Gunst A.W., Hamaker J.P., Hassall T.E.,
Horandel J., van der Horst A., Iacobelli M., Jackson N.J., Juette E.,
Kondratiev V.I., Kuniyoshi M., Maat P., Mann G., McKay-Bukowski D.,
Mevius M., Morganti R., Munk H., Offringa A.R., Orru E., Paas H.,
Pandey V.N., Pietka G., Pizzo R., Polatidis A.G., Renting A., Rowlinson A.,
Schwarz D., Serylak M., Sluman J., Smirnov O., Stappers B.W., Stewart A.,
Swinbank J., Tagger M., Tang Y., Thoudam S., Toribio C., Vermeulen R.,
Vocks C., Zarka P.
<Astrophys. J., 793, 82 (2014)>
=2014ApJ...793...82V 2014ApJ...793...82V (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, Seyfert ; Interferometry ; Surveys ; Radio sources
Keywords: galaxies: active - radio continuum: general - surveys -
techniques: interferometric
Abstract:
We present Low Frequency Array (LOFAR) Low Band observations of the
Bootes and 3C 295 fields. Our images made at 34, 46, and 62 MHz
reach noise levels of 12, 8, and 5 mJy/beam, making them the deepest
images ever obtained in this frequency range. In total, we detect
between 300 and 400 sources in each of these images, covering an area
of 17-52 deg2. From the observations, we derive Euclidean-normalized
differential source counts. The 62 MHz source counts agree with
previous GMRT 153 MHz and Very Large Array 74 MHz differential source
counts, scaling with a spectral index of -0.7. We find that a spectral
index scaling of -0.5 is required to match up the LOFAR 34 MHz source
counts. This result is also in agreement with source counts from the
38 MHz 8C survey, indicating that the average spectral index of radio
sources flattens toward lower frequencies. We also find evidence for
spectral flattening using the individual flux measurements of sources
between 34 and 1400 MHz and by calculating the spectral index averaged
over the source population. To select ultra-steep spectrum (α←1.1)
radio sources that could be associated with massive high-redshift
radio galaxies, we compute spectral indices between 62 MHz, 153 MHz,
and 1.4 GHz for sources in the Bootes field. We cross-correlate
these radio sources with optical and infrared catalogs and fit the
spectral energy distribution to obtain photometric redshifts. We find
that most of these ultra-steep spectrum sources are located in
the 0.7≲z≲2.5 range.
Description:
The Bootes and 3C 295 fields were simultaneously observed on 2012
April 12 as part of a multi-beam observation with the LOFAR LBA
stations. The idea behind the multi-beam setup is that we use the
3C 295 observations as a calibrator field to transfer the gain
amplitudes to the (target) Bootes field. The total integration time on
both fields was 10.25 hr. Complete frequency coverage was obtained
between 54 and 70 MHz for both fields, while non-contiguous frequency
coverage was obtained between 30 and 54 MHz for the 3C 295 only. All
four correlation products were recorded. By default, the frequency
band was divided into sub-bands, each 195.3125 kHz wide. Each sub-band
was further divided in 64 channels and the integration time was 1 s.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
14 11 20.47 +52 12 09.5 3C 295 = 2C 1175
----------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 66 1417 Combined LOFAR Bootes and 3C295
field source catalogs
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See also:
J/AJ/130/923 : Faint radio sources in the NOAO Bootes field (Wrobel+, 2005)
J/A+A/598/A104 : LOFAR Two-metre Sky Survey (Shimwell+, 2017)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Field Field identifier
8- 9 I2 MHz Freq Observational frequency (34, 46 or 62)
11- 26 A16 --- ID Source identifier (JHHMMSS.s+DDMMSS)
28- 36 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000)
38- 41 F4.1 arcsec e_RAdeg The 1σ uncertainty in RAdeg
43- 50 F8.5 deg DEdeg Declination in decimal degrees (J2000)
52- 55 F4.1 arcsec e_DEdeg The 1σ uncertainty in DEdeg
57- 61 I5 mJy S LOFAR flux density at Freq
63- 66 I4 mJy e_S The 1σ uncertainty in S
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 19-Apr-2017