J/ApJ/755/47 Murchison Widefield Array 110-200MHz observations (Williams+ 2012)
Low-frequency imaging of fields at high Galactic latitude with the Murchison
Widefield Array 32 element prototype.
Williams C.L., Hewitt J.N., Levine A.M., de Oliveira-Costa A., Bowman J.D.,
Briggs F.H., Gaensler B.M., Hernquist L.L., Mitchell D.A., Morales M.F.,
Sethi S.K., Subrahmanyan R., Sadler E.M., Arcus W., Barnes D.G.,
Bernardi G., Bunton J.D., Cappallo R.C., Crosse B.W., Corey B.E.,
Deshpande A., deSouza L., Emrich D., Goeke R.F., Greenhill L.J.,
Hazelton B.J., Herne D., Kaplan D.L., Kasper J.C., Kincaid B.B., Koenig R.,
Kratzenberg E., Lonsdale C.J., Lynch M.J., McWhirter S.R., Morgan E.H.,
Oberoi D., Ord S.M., Pathikulangara J., Prabu T., Remillard R.A.,
Rogers A.E.E., Roshi D.A., Salah J.E., Sault R.J., Udaya Shankar N.,
Srivani K.S., Stevens J.B., Tingay S.J., Wayth R.B., Waterson M.,
Webster R.L., Whitney A.R., Williams A.J., Wyithe J.S.B.
<Astrophys. J., 755, 47 (2012)>
=2012ApJ...755...47W 2012ApJ...755...47W
ADC_Keywords: Radio sources ; Interferometry ; Radio continuum ; Surveys
Keywords: dark ages, reionization, first stars;
instrumentation: interferometers; methods: data analysis; surveys
Abstract:
The Murchison Widefield Array (MWA) is a new low-frequency, wide
field-of-view radio interferometer under development at the Murchison
Radio-astronomy Observatory in Western Australia. We have used a 32
element MWA prototype interferometer (MWA-32T) to observe two 50°
diameter fields in the southern sky, covering a total of ∼2700deg2,
in order to evaluate the performance of the MWA-32T, to develop
techniques for epoch of reionization experiments, and to make
measurements of astronomical foregrounds. We developed a calibration
and imaging pipeline for the MWA-32T, and used it to produce ∼15'
angular resolution maps of the two fields in the 110-200MHz band.
We perform a blind source extraction using these confusion-limited
images, and detect 655 sources at high significance with an additional
871 lower significance source candidates. We compare these sources
with existing low-frequency radio surveys in order to assess the
MWA-32T system performance, wide-field analysis algorithms, and
catalog quality. Our source catalog is found to agree well with
existing low-frequency surveys in these regions of the sky and with
statistical distributions of point sources derived from Northern
Hemisphere surveys; it represents one of the deepest surveys to date
of this sky field in the 110-200MHz band.
Description:
The MWA-32T was designed to cover a frequency range from 80MHz to
300MHz, with an instantaneous bandwidth of 30.72MHz at a spectral
resolution of 40kHz. Observations were conducted with the MWA-32T in
2010 March during a two-week campaign. Data were taken in three
30.72MHz sub-bands centered at 123.52MHz, 154.24MHz, and 184.96MHz in
order to give (nearly) continuous frequency coverage between ∼110MHz
and ∼200MHz. The observing time was divided between two fields. One
field was centered on the bright extragalactic source Hydra A at
(J2000)09:18:06-12:5:45 to facilitate calibration. The other covered
the EoR2 field, centered at (J2000)10:20:00-10:00:00.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 108 648 Detected sources in the the Hydra A and EoR2 fields
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See also:
VIII/79 : The VLA Low-frequency Sky Survey at 74MHz (Cohen+ 2007)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
VIII/38 : The Parkes-MIT-NRAO 4.85GHz (PMN) Surveys (Griffith+ 1993-1996)
VIII/18 : 6C Survey of radio sources I. (Baldwin+ 1985)
J/ApJ/734/L34 : 145MHz source measurements by PAPER (Jacobs+, 2011)
J/ApJ/734/98 : DISCS. II. Southern sky disk data (Oberg+, 2011)
J/MNRAS/381/341 : MRCR-SUMSS Ultra-steep-spectrum (USS) cat. (Broderick+, 2007)
J/AJ/123/637 : Ultra-steep-spectrum radio sources (De Breuck +, 2002)
J/AZh/77/21 : 102.5MHz Survey (Dagkesamanskii+, 2000)
J/A+AS/143/303 : Ultra steep spectrum radio sources catalog (De Breuck+ 2000)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- --- [MWA_]
5- 14 A10 --- MWA MWA (Murchison Widefield Array) Source Name
(JHHMM+DDMM)
15- 24 F10.2 deg RAdeg MWA Right Ascension in decimal degrees (J2000)
25- 34 F10.2 deg DEdeg MWA Declination in decimal degrees (J2000)
35- 41 F7.2 Jy SAVG [0.7/714] MWA Source flux density in average
map at 154.24MHz, bandwidth 92MHz (1)
42- 48 F7.2 Jy e_SAVG [0.2/215] SAVG uncertainty (2)
49- 55 F7.2 Jy S124 [0.3/706]? MWA Source flux density in 123.52MHz
map (1)
56- 62 F7.2 Jy e_S124 ? Uncertainty in S124 (2)
63- 69 F7.2 Jy S154 [0.5/653]? MWA Source flux density in 154.24MHz
map (1)
70- 76 F7.2 Jy e_S154 ? Uncertainty in S154 (2)
77- 83 F7.2 Jy S185 [0.5/554]? MWA Source flux density in 184.96MHz
map (1)
84- 90 F7.2 Jy e_S185 ? Uncertainty in S185 (2)
93- 96 A4 --- Field Field (EOR2 of HydA) (4)
97-101 F5.1 deg Rfc [0/25] Source distance from center of field
102-108 F7.1 --- SNR [5/2576] Source signal-to-noise ratio in
detection image (3)
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Note (1): The flux of each source detected in the MWA full-band averaged
maps is presented along with the flux measured in each 30.72MHz
sub-band. Duplicate sources in the region of overlap of the two fields
are not listed. Missing data indicates that the automatic source
measurement algorithm failed to converge in a flux fit for that source
in the sub-band map.
Note (2): We expect systematic errors to be larger for sources far from the
field center.
Note (3): The "Detection SNR Level" indicates the signal-to-noise ratio at
which the source was detected in the full-band averaged map. Section
7.2 discusses the reliability of the catalog at different detection
SNR levels. This list includes sources identified above a detection
SNR threshold of 5. The full source list of all sources above a
detection threshold of 3 is available from the authors.
Note (4): field from which the source measurement is taken:
EOR2 = Epoch of Reionisation #2, centered at J102000-100000
HydA = Hydra A region at J091806-1205045
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 10-Mar-2014