The 6C survey of radio sources - II. The zone Formula

Hales, S. E. G.; Baldwin, John E.; Warner, P. J.

doi:10.1093/mnras/234.4.919

Cited by 141 publications

(131 citation statements)

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“…We found that the combined gain amplitude Cohen et al (2007). (c) Hales et al (1988). (d) Hales et al (2007) and references therein.…”

Section: Astrometric and Flux Uncertaintysupporting

confidence: 62%

“…Further, cluster radio emission usually has steep radio spectra (α < −1), the radiating electrons are old and can provide fossil records of the cluster history (e.g., Miley 1980). Several low-frequency surveys have been performed in the past, such as the Cambridge surveys 3C, 4C, 6C and 7C at 159, 178, 151 and again 151 MHz, respectively (Edge et al 1959;Bennett 1962;Pilkington & Scott 1965;Gower et al 1967;Hales et al 1988Hales et al , 2007, the UTR-2 sky survey between 10-25 MHz (Braude et al 2002), the VLSS at 74 MHz (Cohen et al 2007) A&A 535, A38 (2011) and the ongoing MRT sky survey at 151.5 MHz (e.g., Pandey & Shankar 2007). These surveys are limited in sensitivity and angular resolution, mainly due to man-made RFI, ionospheric phase distortions and wide-field imaging problems.…”

Section: Introductionmentioning

confidence: 99%

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Deep low-frequency radio observations of the NOAO Boötes field

Intema

Weeren

Röttgering

et al. 2011

A&A

103

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In this article we present deep, high-resolution radio interferometric observations at 153 MHz to complement the extensively studied NOAO Boötes field. We provide a description of the observations, data reduction and source catalog construction. From our single pointing GMRT observation of ∼12 h we obtain a high-resolution (26 × 22 ) image of ∼11.3 square degrees, fully covering the Boötes field region and beyond. The image has a central noise level of ∼1.0 mJy beam −1 , which rises to 2.0-2.5 mJy beam −1 at the field edge, placing it amongst the deepest ∼150 MHz surveys to date. The catalog of 598 extracted sources is estimated to be ∼92 percent complete for >10 mJy sources, while the estimated contamination with false detections is <1 percent. The low rms position uncertainty of 1.24 facilitates accurate matching against catalogs at optical, infrared and other wavelengths. Differential source counts are determined down to 10 mJy. There is no evidence for flattening of the counts towards lower flux densities as observed in deep radio surveys at higher frequencies, suggesting that our catalog is dominated by the classical radio-loud AGN population that explains the counts at higher flux densities. Combination with available deep 1.4 GHz observations yields an accurate determination of spectral indices for 417 sources down to the lowest 153 MHz flux densities, of which 16 have ultra-steep spectra with spectral indices below −1.3. We confirm that flattening of the median spectral index towards low flux densities also occurs at this frequency. The detection fraction of the radio sources in NIR K S -band is found to drop with radio spectral index, which is in agreement with the known correlation between spectral index and redshift for brighter radio sources.

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“…We found that the combined gain amplitude Cohen et al (2007). (c) Hales et al (1988). (d) Hales et al (2007) and references therein.…”

Section: Astrometric and Flux Uncertaintysupporting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Deep low-frequency radio observations of the NOAO Boötes field

Intema

Weeren

Röttgering

et al. 2011

A&A

103

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“…The 4.86 and 8.46 GHz values by Fletcher et al (2011) have significant uncertainties due to addition of single dish data to interferometry data. The integrated flux of M 51 from the 6C (Hales et al 1988) (6.90 ± 0.69 Jy) and 7C (Waldram et al 1996) (6.48 ± 0.65 Jy) surveys are very comparable the flux of the star forming region of M 51 (6.98 Jy).…”

Section: Integrated Radio Continuum Spectrummentioning

confidence: 65%

“…(1) Klein et al (1984); (2) Klein & Emerson (1981); (3) Dumas et al (2011); (4) Fletcher et al (2011); (5) Segalovitz (1977); (6) Gioia & Gregorini (1980); (7) Hales et al (1988); (8) Waldram et al (1996).…”

Section: Integrated Radio Continuum Spectrumunclassified

The nature of the low-frequency emission of M 51

Mulcahy

Horneffer²,

Beck³

et al. 2014

A&A

113

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Context. Low-frequency radio continuum observations (<300 MHz) can provide valuable information on the propagation of low-energy cosmic ray electrons (CRE). Nearby spiral galaxies have hardly been studied in this frequency range because of the technical challenges of low-frequency radio interferometry. This is now changing with the start of operations of LOFAR. Aims. We aim to study the propagation of low-energy CRE in the interarm regions and the extended disk of the nearly face-on spiral galaxy Messier 51. We also search for polarisation in M 51 and other extragalactic sources in the field. Methods. The grand-design spiral galaxy M 51 was observed with the LOFAR High Frequency Antennas (HBA) and imaged in total intensity and polarisation. This observation covered the frequencies between 115 MHz and 175 MHz with 244 subbands of 8 channels each, resulting in 1952 channels. This allowed us to use RM synthesis to search for polarisation. Results. We produced an image of total emission of M 51 at the mean frequency of 151 MHz with 20 resolution and 0.3 mJy rms noise, which is the most sensitive image of a galaxy at frequencies below 300 MHz so far. The integrated spectrum of total radio emission is described well by a power law, while flat spectral indices in the central region indicate thermal absorption. We observe that the disk extends out to 16 kpc and see a break in the radial profile near the optical radius of the disk. The radial scale lengths in the inner and outer disks are greater at 151 MHz, and the break is smoother at 151 MHz than those observed at 1.4 GHz. The arm-interarm contrast is lower at 151 MHz than at 1400 MHz, indicating propagation of CRE from spiral arms into interarm regions. The correlations between the images of radio emission at 151 MHz and 1400 MHz and the FIR emission at 70 μm reveal breaks on scales of 1.4 and 0.7 kpc, respectively. The total (equipartition) magnetic field strength decreases from about 28 μG in the central region to about 10 μG at 10 kpc radius. No significant polarisation was detected from M 51, owing to severe Faraday depolarisation. Six extragalactic sources are detected in polarisation in the M 51 field of 4.1 • × 4.1 • size. Two sources show complex structures in Faraday space. Conclusions. Our main results, the scale lengths of the inner and outer disks at 151 MHz and 1.4 GHz, arm-interarm contrast, and the break scales of the radio-FIR correlations, can be explained consistently by CRE diffusion, leading to a longer propagation length of CRE of lower energy. The distribution of CRE sources drops sharply at about 10 kpc radius, where the star formation rate also decreases sharply. We find evidence that thermal absorption is primarily caused by H ii regions. The non-detection of polarisation from M 51 at 151 MHz is consistent with the estimates of Faraday depolarisation. Future searches for polarised emission in this frequency range should concentrate on regions with low star formation rates.Key words. polarization -cosmic rays -galaxies: ISM -galaxies: ...

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“…An additional constraint on our models down to S151 ≈ 0.1 Jy comes from the 151 MHz source counts from the 7C and 6C surveys (McGilchrist et al 1990 andHales, Baldwin &Warner 1988, respectively). Since these counts include both quasars and radio galaxies, the source counts predicted from our quasar RLF models must be significantly lower.…”

Section: Press Et Al (1992) It Gives the Probability Pks That Thementioning

confidence: 99%

The radio luminosity function of radio-loud quasars from the 7C Redshift Survey

Rawlings

Blundell

Lacy

1998

Monthly Notices of the Royal Astronomical Society

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We present a complete sample of 24 radio-loud quasars (RLQs) from the new 7C Redshift Survey. Every quasar with a low-frequency (151 MHz) radio flux-density S 151 > 0.5 Jy in two regions of the sky covering 0.013 sr is included; 23 of these have sufficient extended flux to meet the selection criteria, 18 of these have steep radio spectra (hereafter denoted as SSQs). The key advantage of this sample over most samples of RLQs is the lack of an optical magnitude limit. By combining the 7C and 3CRR samples, we have investigated the properties of RLQs as a function of redshift z and radio luminosity L 151 .We derive the radio luminosity function (RLF) of RLQs and find that the data are well fitted by a single power-law with slope α 1 = 1.9 ± 0.1 (for H • = 50 km s −1 Mpc −1 , Ω M = 1, Ω Λ = 0). We find that there must be a break in the RLQ RLF at log 10 (L 151 / W Hz −1 sr −1 ) < ∼ 27, in order for the models to be consistent with the 7C and 6C source counts. The z-dependence of the RLF follows a one-tailed gaussian which peaks at z = 1.7 ± 0.2. We find no evidence for a decline in the co-moving space density of RLQs at higher redshifts.A positive correlation between the radio and optical luminosities of SSQs is observed, confirming a result of Serjeant et al. (1998). We are able to rule out this correlation being due to selection effects or biases in our combined sample. The radiooptical correlation and best-fit model RLF enable us to estimate the distribution of optical magnitudes of quasars in samples selected at low radio frequencies. We conclude that for samples with S 151 < ∼ 1 Jy one must use optical data significantly deeper than the POSS-I limit (R ≈ 20), in order to avoid severe incompleteness.

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The 6C survey of radio sources - II. The zone Formula

Cited by 141 publications

References 0 publications

Deep low-frequency radio observations of the NOAO Boötes field

Deep low-frequency radio observations of the NOAO Boötes field

The nature of the low-frequency emission of M 51

The radio luminosity function of radio-loud quasars from the 7C Redshift Survey

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