J/MNRAS/394/2197 Distant radio galaxies in southern hemisphere (Bryant+, 2009)
A new search for distant radio galaxies in the southern hemisphere.
II. 2.2µm imaging.
Bryant J.J., Broderick J.W., Johnston H.M., Hunstead R.W., Gaensler B.M.,
De Breuck C.
<Mon. Not. R. Astron. Soc., 394, 2197-2222 (2009)>
=2009MNRAS.394.2197B 2009MNRAS.394.2197B
ADC_Keywords: Surveys ; Galaxies, radio ; Photometry, infrared ; Morphology
Keywords: surveys - galaxies: active - galaxies: high-redshift -
infrared: galaxies - radio continuum: galaxies
Abstract:
We have compiled a sample of 234 ultra-steep-spectrum (USS) selected
radio sources in order to find high-redshift radio galaxies. The
sample covers the declination range -40°<δ←30° in the
overlap region between the 1400-MHz National Radio Astronomy
Observatory (NRAO) Very Large Array (VLA) Sky Survey (NVSS), 408-MHz
Revised Molonglo Reference Catalogue and the 843-MHz Sydney University
Molonglo Sky Survey (the MRCR-SUMSS sample). This is the second in a
series of papers on the MRCR-SUMSS sample, and here we present the
K-band (2.2µm) imaging of 173 of the sources primarily from the
Magellan and the Anglo-Australian Telescopes. We detect a counterpart
to the radio source in 93 per cent of the new K-band images which,
along with previously published data, makes this the largest published
sample of K-band counterparts to USS-selected radio galaxies. The
location of the K-band identification has been compared to the
features of the radio emission for the double sources. We find that
the identification is most likely to lie near the mid-point of the
radio lobes rather than closer to the brighter lobe, making the
centroid a less likely place to find the optical counterpart. 79 per
cent of the identifications are less than 1arcsec from the radio lobe
axis. These results differ from studies of low-redshift radio samples
where the environments are typically not nearly so dense and disturbed
as those at high redshift. In contrast to some literature samples, we
find that the majority of our sample shows no alignment between the
near-infrared and radio axes. Several different morphologies of
aligned structures are found and those that are aligned within 10°
are consistent with jet-induced star formation. The distribution and
median value of the K-band magnitudes for the MRCR-SUMSS sample are
found to be similar to several other USS-selected samples even though
each sample has a very different median 1400MHz flux density. USS
selection from a lower radio-frequency sample has not netted fainter
K-band magnitudes, which may imply that the k-correction is not
responsible for the effectiveness of USS selection.
Description:
Radio images were obtained with the Australia Telescope Compact Array
(ATCA) in several runs in 2003-06. Both 1384- and 2368-MHz images
were needed to pinpoint the K-band identification.
Higher resolution observations were obtained for 29 sources on UT 2008
January 16-20. Our initial Ks-band imaging was begun on the 3.9-m
Anglo-Australian Telescope's (AAT) Infrared Imager and Spectrograph
(IRIS2) detector on two observing runs on 2004 August 3-5 and 2005
June 21-24.
We observed 126 targets in Ks-band with Persson's Auxiliary Nasmyth
Infrared Camera (PANIC;) on the 6.5-m Magellan Baade telescope at Las
Campanas Observatory on 2006 June 11-13, 2006 November 8-10 and
2007 April 2-4.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 95 177 K-band photometry results
table3.dat 71 29 4800- and 8640-MHz ATCA radio properties
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See also:
J/MNRAS/347/837 : Radio & K-band obs. of Ultra-Steep sources (De Breuck+, 2004)
J/MNRAS/381/341 : MRCR-SUMSS Ultra-steep-spectrum sample (Broderick+, 2007)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- --- [NVSS]
6- 19 A14 --- NVSS NVSS name (JHHMMSS+DDMMSS)
20 A1 --- n_NVSS [ahi] Note on NVSS (1)
22 A1 --- l_K4mag Limit flag on Kmag
23- 26 F4.1 mag K4mag ? K magnitude in 4" diameter-aperture
28- 30 F3.1 mag e_K4mag ? rms uncertainty on K4mag
31- 33 A3 --- n_K4mag [SC, de] Note on K4mag (1)
35- 38 F4.1 mag K8mag ? K magnitude in 8" diameter-aperture
40- 42 F3.1 mag e_K8mag ? rms uncertainty on K8mag
44- 45 I2 h RAh ? Right ascension from K band (J2000) (2)
47- 48 I2 min RAm ? Right ascension from K band (J2000) (2)
50- 54 F5.2 s RAs ? Right ascension from K band (J2000) (2)
56 A1 --- DE- Declination sign from K band (J2000) (2)
57- 58 I2 deg DEd ? Declination from K band (J2000) (2)
60- 61 I2 arcmin DEm ? Declination from K band (J2000) (2)
63- 66 F4.1 arcsec DEs ? Declination from K band (J2000) (2)
67 A1 --- pos [bck] Origin of the position (1)
69- 70 I2 min Tint [3/99]?=- K-band image exposure time
72- 76 A5 --- Src Origin of K imaging (3)
79- 83 F5.2 --- alpha [-1.9/-0.3]? Spectral index α from the
five-point fit from Paper I (4)
85- 88 F4.2 --- e_alpha [0.04/0.12]?=- rms uncertainty on alpha
89 A1 --- n_alpha [fjg] Note on alpha (1)
91 A1 --- l_LAS Limit flag on LAS
92- 95 F4.1 arcsec LAS [1/73]? Largest angular size from the
natural-weighted 2368MHz image
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Note (1): Notes as follows:
a = Two NVSS sources have been shown to be the components of a
single radio source
b = SuperCOSMOS optical position
c = 2MASS position
d = Obscured by an M star (see Paper III, 2009MNRAS.395.1099B 2009MNRAS.395.1099B)
e = 2MASS K magnitude in 8-arcsec aperture
g = Spectral indices from Klamer et al. (2006MNRAS.371..852K 2006MNRAS.371..852K)
f = fitted spectral index at 1400MHz for sources with spectra that flatten
at higher frequencies
h = These sources were observed by De Breuck et al. (2004MNRAS.347..837D 2004MNRAS.347..837D,
Cat. J/MNRAS/347/837, 2006MNRAS.366...58D 2006MNRAS.366...58D) in the SUMSS-NVSS sample with
no detection in K band. We have re-observed them and improved the
magnitude limit for NVSS J230527-360534.
i = These sources were also part of the SUMSS-NVSS sample (De Breuck et al.
2004MNRAS.347..837D 2004MNRAS.347..837D, Cat. J/MNRAS/347/837, 2006MNRAS.366...58D 2006MNRAS.366...58D), and
therefore were not re-observed in K band. The K-band magnitudes and
positions given are from De Breuck et al. (2004MNRAS.347..837D 2004MNRAS.347..837D,
Cat. J/MNRAS/347/837).
j = α1400843 where 5-point was not available from Paper I
(2007MNRAS.381..341B 2007MNRAS.381..341B, Cat. J/MNRAS/381/341). For the sources from
De Breuck et al. (2004MNRAS.347..837D 2004MNRAS.347..837D, Cat. J/MNRAS/347/837), the
spectral index has been recalculated using updated SUMSS flux
measurements from the latest release.
k = position of the object discussed in Section 3.2, which may be a star
SC = sources without K
Note (2): No position for sources that had no K-band or SuperCOSMOS
identification.
Note (3): origin of the K-band image as follows:
PANIC = PANIC on the Magellan Baade Telescope
IRIS2 = IRIS2 on the AAT
DB = sources from De Breuck et al. (2004MNRAS.347..837D 2004MNRAS.347..837D, J/MNRAS/347/837)
SC = sources without K, which were identified on the SuperCOSMOS UKJ
and UKR fields
2MASS = two objects from the 2MASS catalogue
Note (4): Some sources have spectral shapes that could not be fitted with a
five-point linear or quadratic fit and the spectral index between 843 and
1400MHz is shown instead. For the sources from De Breuck et al.
(2004MNRAS.347..837D 2004MNRAS.347..837D, Cat. J/MNRAS/347/837), the spectral index has been
recalculated using updated flux densities from the latest SUMSS catalogue
release (version 2.1). Sources with flattening radio spectra at high
frequencies (marked f) have a spectral index fitted at 1400MHz (see Paper I,
2007MNRAS.381..341B 2007MNRAS.381..341B, Cat. J/MNRAS/381/341). The spectral indices from
Klamer et al. (2006MNRAS.371..852K 2006MNRAS.371..852K), used for the sources marked g, are the
result of fits to flux densities at up to seven frequencies between
0.843-18GHz.
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- --- [NVSS]
6- 19 A14 --- NVSS NVSS name (JHHMMSS+DDMMSS)
21- 24 F4.1 mJy S4.8 4800MHz integrated flux density
26- 28 F3.1 mJy e_S4.8 rms uncertainty on S4.8
30- 33 F4.1 mJy S8.6 8640MHz integrated flux density
35- 37 F3.1 mJy e_S8.6 rms uncertainty on S8.6
39- 43 F5.2 --- alpha1 [-2/0.6] Two point observed-frame spectral
index α86404800
45- 48 F4.2 --- e_alpha1 [0.1/0.4] rms uncertainty on alpha1
50- 54 F5.2 --- alpha2 [-1.5/0.9]?=- Seven-point observed-frame
spectral index α (1)
56- 59 F4.2 --- e_alpha2 [0.02/0.03]? rms uncertainty on alpha2
60 A1 --- n_alpha2 [f] f for sources that have curved spectra
that flatten at high frequency (2)
62 A1 --- l_LAS Limit flag on LAS
63- 66 F4.1 arcsec LAS [0.9/33]Largest angular size (3)
67 A1 --- n_LAS [a] a: LAS obtained from 2368MHz image
69- 71 I3 deg PA [-90/90]? Deconvolved position angle of the
radio structure, measured from the north to
the east (4)
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Note (1): based on a linear fit to the 408, 843, 1384, 1400 and 2368MHz flux
densities from Paper I (2007MNRAS.381..341B 2007MNRAS.381..341B, Cat. J/MNRAS/381/341), as well
as the 4800 and 8640MHz data points.
Note (2): For sources that have curved spectra that flatten at high frequency,
we use a quadratic fit to all seven data points to derive the observed-frame
spectral index at 1400MHz.
Note (3): For single-component resolved sources, this is the deconvolved major
axis of the elliptical Gaussian used to fit the source. For unresolved
sources, we estimate a LAS upper limit of 1-arcsec. For multicomponent
sources, the LAS is the angular separation of the most widely separated
components.
Note (4): For multicomponent sources, this is the orientation of the most
widely separated components used to calculate the LAS.
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History:
From electronic version of the journal
References:
Broderick et al., Paper I 2007MNRAS.381..341B 2007MNRAS.381..341B, Cat. J/MNRAS/381/341
Bryant et al., Paper III 2009MNRAS.395.1099B 2009MNRAS.395.1099B
(End) Patricia Vannier [CDS] 08-Jun-2015