J/A+A/620/A74 Bootes field deep LOFAR 150MHz imaging (Retana-Montenegro+, 2018)
Deep LOFAR 150 MHz imaging of the Bootes field:
Unveiling the faint low-frequency sky.
Retana-Montenegro E., Rottgering H.J.A, Shimwell T.W., van Weeren R.J.,
Prandoni I., Brunetti G., Best P.N, Bruggen M.
<Astron. Astrophys. 620, A74 (2018)>
=2018A&A...620A..74R 2018A&A...620A..74R (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Galaxies, radio ; Radio continuum
Keywords: surveys - catalogs - radio continuum: general -
techniques: image processing
Abstract:
We have conducted a deep survey (with a central rms of 55uJy) with the
LOw Frequency ARray (LOFAR) at 120-168MHz of the Bootes field, with an
angular resolution of 3.98"x6.45", and obtained a sample of 10091
radio sources (5σ limit) over an area of 20deg2. The
astrometry and flux scale accuracy of our source catalog is
investigated. The resolution bias, incompleteness and other systematic
effects that could affect our source counts are discussed and
accounted for. The derived 150MHz source counts present a flattening
below sub-mJy flux densities, that is in agreement with previous
results from high- and low- frequency surveys. This flattening has
been argued to be due to an increasing contribution of star-forming
galaxies and faint active galactic nuclei. Additionally, we use our
observations to evaluate the contribution of cosmic variance to the
scatter in source counts measurements. The latter is achieved by
dividing our Bootes mosaic into 10 non-overlapping circular sectors,
each one with an approximate area of 2deg2. The counts in each
sector are computed in the same way as done for the entire mosaic. By
comparing the induced scatter with that of counts obtained from depth
observations scaled to 150MHz, we find that the 1σ scatter due
to cosmic variance is larger than the Poissonian errors of the source
counts, and it may explain the dispersion from previously reported
depth source counts at flux densities S<1mJy. This work demonstrates
the feasibility of achieving deep radio imaging at low-frequencies
with LOFAR.
Description:
The LOFAR mosaic image of the Bootes field and its corresponding
source catalog are presented here. The mosaic image is obtained using
55 hours of observations, and it has a central rms noise of
0.255mJy/beam and an angular resolution of 3.98"x6.45".
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 117 10091 LOFAR source catalog
list.dat 117 1 Information on fits image
fits/* . 1 Fits image
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See also:
J/AJ/123/1784 : 1.4GHz imaging of the Bootes field (de Vries+, 2002)
J/AJ/127/213 : LALA Bootes field X-ray source catalog (Wang+, 2004)
J/AJ/130/923 : Faint radio sources in the NOAO Bootes field (Wrobel+, 2005)
J/ApJ/634/L1 : 16µm sources in the NOAO Bootes field (Kasliwal+, 2005)
J/ApJS/161/9 : X-ray survey of the NDWFS Bootes field (Kenter+, 2005)
J/ApJ/641/140 : Optical counterparts in the NDWFS Bootes field (Brand+ 2006)
J/A+A/535/A38 : Observations of NOAO Bootes field at 153MHz (Intema+, 2011)
J/ApJ/793/82 : LOFAR Bootes and 3C295 field sources (van Weeren+, 2014)
J/MNRAS/450/1477 : VLA 352MHz image of the Bootes field. I. (Coppejans+, 2015)
J/ApJ/817/119 : Bootes field Spitzer/IRAC variability survey
(Kozlowski+, 2016)
J/MNRAS/460/2385 : Bootes field LOFAR 150-MHz observations (Williams+, 2016)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- SourceID Source name (JHHMMSS.ss+DDMMSS.s)
(Source_ID)
21- 28 F8.4 deg RAdeg Right ascension (J2000) (RA)
30- 37 F8.4 deg e_RAdeg rms uncertainty on RAdeg (E_RA)
39- 45 F7.4 deg DEdeg Declination (J2000) (DEC)
47- 55 F9.4 deg e_DEdeg rms uncertainty on DEdeg (E_DEC)
57- 65 F9.4 mJy Ftotal Integrated source flux density at 150MHz
(Ftotal)
67- 74 F8.4 mJy e_Ftotal rms uncertainty on Ftotal (e_Ftotal)
76- 84 F9.4 mJy/beam Fpeak Peak flux density at 150MHz
86- 93 F8.4 mJy/beam e_Fpeak rms uncertainty on Fpeak (e_Fpeak)
95-100 F6.4 --- Fsmear Approximate correction factor to the peak
flux density to account for bandwidth-
and time-smearing (Fsmear)
102-107 F6.4 mJy/beam rms Local rms noise used for the source
detection (rms)
109 A1 --- Type [R/U] flag indicating if the source is
resolved (R) or unresolved (U) (1)
111 A1 --- PyBDSF [S/M] flag indicating the source structure
code by PyBDSF (PyBDSF_code) (2)
113 I1 --- Edge [0/1] an object that is located close to
or in a facet edge, which could result
in some flux loss (Flag_edge)
115 I1 --- Artifact [0/2] a source is identified as an artefact
(Flag_artifact) (3)
117 I1 --- Merged [0/1] a large diffuse source whose separate
components are merged into a single one
according to a visual inspection
(Flag_merged)
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Note (1): flag indicating the resolved parametrization of the source as follows:
U = unresolved sources
R = resolved sources
Note (2): flag indicating the indicating the source structure code by PyBDSF
as follows:
S = a source with a single component
M = a source with multiple components
Note (3): artifact flag as follows:
0 = no artifact
1 = a source that is probably an artifact
2 = a source that is surely an artifact
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 24 I5 --- Nx Number of pixels along X-axis
26- 30 I5 --- Ny Number of pixels along Y-axis
32- 52 A21 --- Obs.Date Observation date (YYYY-MM-DDThh:mm:ss.s)
54- 60 F7.3 MHz Freq Observed frequency
62- 68 I7 Kibyte size Size of FITS file
70- 93 A24 --- FileName Name of FITS file, in subdirectory fits
95-117 A23 --- Title Title of the FITS file
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Acknowledgements:
Edwin Retana, edwinretana(at)gmail.com
(End) Patricia Vannier [CDS] 20-Aug-2018