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J/MNRAS/429/2080 Lockman Hole 10C sources radio spectral indices (Whittam+ 2013)
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The faint source population at 15.7 GHz. I. The radio properties.
Whittam I.H., Riley J.M., Green D.A., Jarvis M.J., Prandoni I.,
Guglielmino G., Morganti R., Rottgering H.J.A., Garrett M.A.

=2013MNRAS.429.2080W (SIMBAD/NED BibCode)
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ADC_Keywords: Surveys ; Radio sources ; Radio continuum
Keywords: galaxies: active - galaxies: starburst - radio continuum: galaxies

Abstract:
We have studied a sample of 296 faint (>0.5mJy) radio sources
selected from an area of the Tenth Cambridge (10C) survey at 15.7GHz
in the Lockman Hole. By matching this catalogue to several lower
frequency surveys (e.g. including a deep GMRT survey at 610MHz, a
WSRT survey at 1.4GHz, NVSS, FIRST and WENSS) we have investigated
the radio spectral properties of the sources in this sample; all but
30 of the 10C sources are matched to one or more of these surveys. We
have found a significant increase in the proportion of flat spectrum
sources at flux densities below 1mJy - the median spectral index
between 15.7GHz and 610MHz changes from 0.75 for flux densities
greater than 1.5mJy to 0.08 for flux densities less than 0.8mJy.
This suggests that a population of faint, flat spectrum sources is
emerging at flux densities around 1mJy.

The spectral index distribution of this sample of sources selected at
15.7GHz is compared to those of two samples selected at 1.4GHz from
FIRST and NVSS. We find that there is a significant flat spectrum
population present in the 10C sample which is missing from the samples
selected at 1.4GHz. The 10C sample is compared to a sample of sources
selected from the SKADS Simulated Sky by Wilman et al.
(2008MNRAS.388.1335W) and we find that this simulation fails to
reproduce the observed spectral index distribution and significantly
underpredicts the number of sources in the faintest flux density bin.
It is likely that the observed faint, flat spectrum sources are a
result of the cores of FRI sources becoming dominant at high
frequencies. These results highlight the importance of studying this
faint, high frequency population.

Description:
Flux densities at 15.7GHz, 1.4GHz and 610MHz along with radio spectral
indices are given for 296 sources selected at 15.7GHz from the Lockman
Hole fields of the Tenth Cambridge (10C) survey (AMI Consortium:
Davies et al. 2011, Cat. J/MNRAS/415/2708, AMI Consortium: Franzen et
al. 2011MNRAS.415.2699F). All 610-MHz flux densities come from the
GMRT survey by Garn et al. (2008, Cat. J/MNRAS/387/1037, 2010, Cat.
J/other/BASI/38.103). For extended sources the original images have
been smoothed to a comparable resolution to the 10C survey (30-arcsec)
before the flux density is extracted to make the flux densities at
15.7GHz and 610MHz more directly comparable. For 10C sources without a
counterpart in the GMRT image, three times the local noise is included
as an upper limit on the flux density at 610MHz. For these sources,
the value of the column 'f_S610' is 1 (meaning the value in 'S610' is
an upper limit, not a detection). Five sources lie outside the GMRT
survey area so 610MHz data is not available for these sources. The
1.4-GHz flux density values come from a number of different
catalogues, in the following order of preference: NVSS, FIRST, WSRT
catalogue (Guglielmino et al. 2012, in prep), Owen and Morrison (2008,
Cat. J/AJ/136/1889), Biggs and Ivison (2008, Cat. J/MNRAS/371/963),
upper limit from WSRT catalogue the upper limit from FIRST. The value
of 'f_S1.4best' indicates which catalogue the 1.4-GHz flux density
value originates from. 1.4-GHz values are also included using NVSS
values only - in this case, for 10C sources without a counterpart in
the NVSS catalogue an upper limit of three times the local noise in
the NVSS map was placed on the 1.4-GHz flux density. The value of
'f_SNVSS' indicates whether the flux density value is an upper limit
(1) or a detection (0). The relevent radio spectral indices are also
included.

Note that this catalogue contains sources which are not in the
original 10C catalogue as they are below the completeness limit.

File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 94 296 Flux density and spectral index information for
296 sources
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See also:
J/MNRAS/371/963 : Lockman Hole, HDFN, ELAISN2 deep VLA survey (Biggs+ 2006)
J/AJ/136/1889 : 20cm observations of deep Swire Field (Owen+, 2008)
J/MNRAS/387/1037 : Lockman Hole with GMRT 610-MHz survey (Garn+, 2008)
J/other/BASI/38.103 : Lockman Hole with GMRT 610-MHz survey. II. (Garn+, 2010)
J/MNRAS/415/2708 : 10C survey of radio sources at 15.7GHz (Davies+, 2011)

Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- --- [10C]
4- 17 A14 --- Name ID from 10C catalogue (JHHMMSS+DDMMSS)
19- 20 I2 h RAh Right Ascension J2000 (from 10C catalogue)
22- 23 I2 min RAm Right Ascension J2000
25- 29 F5.2 s RAs Right Ascension J2000
31 A1 --- DE- Declination sign J2000
32- 33 I2 deg DEd Declination J2000
35- 36 I2 arcmin DEm Declination J2000
38- 42 F5.2 arcsec DEs Declination J2000
44- 49 F6.3 mJy S10C 15.7-GHz flux density from 10C catalogue (1)
51- 56 F6.2 mJy S610 ? 610-MHz flux density from GMRT catalogue,
including upper limits for undetected sources
58 I1 --- f_S610 [0/1]? S610 value is a detection (0) or
an upper limit (1)
60- 65 F6.2 mJy S1.4best Best 1.4-GHz flux density value, including
upper limits (2)
67 I1 --- f_S1.4best [0/7] Indicates which catalogue S1.4best value
originates from and which values are
upper limits (3)
69- 74 F6.2 mJy SNVSS ? 1.4-GHz flux density value from NVSS
catalogue, including upper limits for
undetected sources
76 I1 --- f_SNVSS [0/1]? SNVSS value is a detection (0) or
an upper limit (1)
78- 82 F5.2 --- alpha1 ? Radio spectral index between 15.7GHz and
610MHz, calculated from S10C and S610
(upper limits are included)
84- 88 F5.2 --- alpha2 ? Radio spectral index between 15.7GHz and
1.4GHz, calculated from S10C and S1.4best
(upper limits are included)
90- 94 F5.2 --- alpha3 ? Radio spectral index between 15.7GHz and
1.4GHz, using values from NVSS catalogue,
calculated from S10C and SNVSS
(includes upper limits)
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Note (1): Peak flux density for sources listed as point sources in the 10C
catalogue, integrated flux density for sources listed as extended
in the 10C catalogue.
Note (2): 1.4-GHz values are included in the following order of preference:
NVSS, FIRST, WSRT catalogue (Guglielmino et al. 2012, in prep),
Owen and Morrison (2008, Cat. J/AJ/136/1889),
Biggs and Ivison (2008, Cat. J/MNRAS/371/963),
upper limit from WRST data the upper limit from FIRST.
The value used is indicated by the value of f_S1.4best.
Note (3): Flag on S1.4best as follows:
1 = NVSS, Cat. VIII/65
2 = WSRT catalogue (Guglielmino et al., in prep)
3 = VLA catalogue (Owen and Morrison, 2008, Cat. J/AJ/136/1889)
4 = VLA catalogue (Biggs and Ivison, 2008, Cat. J/MNRAS/371/963)
5 = FIRST, Cat. VIII/90
6 = limit from WSRT data
7 = limit from FIRST data
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Acknowledgements:
Imogen Whittam, ihw24(at)cam.ac.uk

History:
* 21-May-2013: on-line version
* 20-Jun-2013: data for 10CJ104656+594639 completed (from author)

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(End) Imogen Whittam [MRAO], Patricia Vannier [CDS] 21-Jun-2013