T-RaMiSu: the Two-meter Radio Mini Survey

Williams, W. L.; Intema, H. T.; Röttgering, H. J. A.

doi:10.1051/0004-6361/201220235

Cited by 61 publications

(83 citation statements)

References 48 publications

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“…In the Boötes field, faint diffuse emission is found at 14 h 21. m 5 +35 • 12 , labeled with a circle in Figure 4. This source (1421+35) was previously also noted by Delain & Rudnick (2006) and Williams et al (2013). A more detailed study of the source was performed by de Gasperin et al (2014).…”

Section: Resultssupporting

confidence: 58%

“…For the Boötes field, the calibration model is derived from a deep GMRT 153 MHz image (Williams et al 2013) using the PyBDSM source detection software. 53…”

Section: Boötes Fieldmentioning

confidence: 99%

“…Recently, most deep low-frequency surveys have been carried out with the GMRT at around 150 MHz (e.g., Ishwara-Chandra & Marathe 2007;Sirothia et al 2009;Ishwara-Chandra et al 2010;Intema et al 2011;Williams et al 2013). These surveys reach a rms noise level of the order of a mJy per beam.…”

Section: Introductionmentioning

confidence: 99%

“…Both the Boötes field and the Groth strip have been extensively studied at higher radio frequencies and other parts of the electromagnetic spectrum. For the Boötes field, observations have been carried out at 153 MHz (Intema et al 2011;Williams et al 2013), 325 MHz (Croft et al 2008), 1.4 GHz (de Vries et al 2002Higdon et al 2005), and 3.1 GHz (Croft et al 2013). The Groth strip has been observed at 1.4 GHz (Ivison et al 2007).…”

Section: Introductionmentioning

confidence: 99%

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Lofar Low-Band Antenna Observations of the 3c 295 and Boötes Fields: Source Counts and Ultra-Steep Spectrum Sources

Weeren

Williams

Tasse

et al. 2014

ApJ

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We present Low Frequency Array (LOFAR) Low Band observations of the Boötes and 3C 295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy beam −1 , making them the deepest images ever obtained in this frequency range. In total, we detect between 300 and 400 sources in each of these images, covering an area of 17-52 deg 2 . From the observations, we derive Euclidean-normalized differential source counts. The 62 MHz source counts agree with previous GMRT 153 MHz and Very Large Array 74 MHz differential source counts, scaling with a spectral index of −0.7. We find that a spectral index scaling of −0.5 is required to match up the LOFAR 34 MHz source counts. This result is also in agreement with source counts from the 38 MHz 8C survey, indicating that the average spectral index of radio sources flattens toward lower frequencies. We also find evidence for spectral flattening using the individual flux measurements of sources between 34 and 1400 MHz and by calculating the spectral index averaged over the source population. To select ultra-steep spectrum (α < −1.1) radio sources that could be associated with massive high-redshift radio galaxies, we compute spectral indices between 62 MHz, 153 MHz, and 1.4 GHz for sources in the Boötes field. We cross-correlate these radio sources with optical and infrared catalogs and fit the spectral energy distribution to obtain photometric redshifts. We find that most of these ultra-steep spectrum sources are located in the 0.7 z 2.5 range.

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Section: Resultssupporting

confidence: 58%

“…For the Boötes field, the calibration model is derived from a deep GMRT 153 MHz image (Williams et al 2013) using the PyBDSM source detection software. 53…”

Section: Boötes Fieldmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Lofar Low-Band Antenna Observations of the 3c 295 and Boötes Fields: Source Counts and Ultra-Steep Spectrum Sources

Weeren

Williams

Tasse

et al. 2014

ApJ

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“…We note that weighting the source count with area only affects the lowest flux density bin (because the other sources are bright enough to be detected over the entire image). Our finding agrees with the areal density of sources obtained from multiple GMRT observations of a 30 deg 2 region, centered on the Bootes field (Williams et al 2013). No deviations from a single power law are observed, suggesting that a single population (i.e., an AGN) dominates our sample.…”

Section: Source Countssupporting

confidence: 90%

Wide-field LOFAR imaging of the field around the double-double radio galaxy B1834+620

Orrù

Velzen

Pizzo

et al. 2015

A&A

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Context. The existence of double-double radio galaxies (DDRGs) is evidence for recurrent jet activity in active galactic nuclei (AGN), as expected from standard accretion models. A detailed study of these rare sources provides new perspectives for investigating the AGN duty cycle, AGN-galaxy feedback, and accretion mechanisms. Large catalogues of radio sources, on the other hand, provide statistical information about the evolution of the radio-loud AGN population out to high redshifts. Aims. Using wide-field imaging with the LOFAR telescope, we study both a well-known DDRG as well as a large number of radio sources in the field of view. Methods. We present a high resolution image of the DDRG B1834+620 obtained at 144 MHz using LOFAR commissioning data. Our image covers about 100 square degrees and contains over 1000 sources. Results. The four components of the DDRG B1834+620 have been resolved for the first time at 144 MHz. Inner lobes were found to point towards the direction of the outer lobes, unlike standard FR II sources. Polarized emission was detected at +60 rad m −2 in the northern outer lobe. The high spatial resolution allows the identification of a large number of small double-lobed radio sources; roughly 10% of all sources in the field are doubles with a separation smaller than 1 . Conclusions. The spectral fit of the four components is consistent with a scenario in which the outer lobes are still active or the jets recently switched off, while emission of the inner lobes is the result of a mix-up of new and old jet activity. From the presence of the newly extended features in the inner lobes of the DDRG, we can infer that the mechanism responsible for their formation is the bow shock that is driven by the newly launched jet. We find that the density of the small doubles exceeds the density of FR II sources with similar properties at 1.4 GHz, but this difference becomes smaller for low flux densities. Finally, we show that the significant challenges of wide-field imaging (e.g., time and frequency variation of the beam, directional dependent calibration errors) can be solved using LOFAR commissioning data, thus demonstrating the potential of the full LOFAR telescope to discover millions of powerful AGN at redshift z ∼ 1.

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The Lockman Hole with LOFAR: Searching for GPS and CSS sources at low frequencies

et al. 2016

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The Lockman Hole Project is a wide international collaboration aimed at exploiting the multi‐band extensive and deep information available for the Lockman Hole region, with the aim of better characterizing the physical and evolutionary properties of the various source populations detected in deep radio fields. Recent observations with the LOw‐Frequency ARray (LOFAR) extends the multi‐frequency radio information currently available for the Lockman Hole (from 350 MHz up to 15 GHz) down to 150 MHz, allowing us to explore a new radio spectral window for the faint radio source population. These LOFAR observations allow us to study the population of sources with spectral peaks at lower radio frequencies, providing insight into the evolution of GPS and CSS sources. In this general framework, I present preliminary results from 150 MHz LOFAR observations of the Lockman Hole field. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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T-RaMiSu: the Two-meter Radio Mini Survey

Cited by 61 publications

References 48 publications

Lofar Low-Band Antenna Observations of the 3c 295 and Boötes Fields: Source Counts and Ultra-Steep Spectrum Sources

Lofar Low-Band Antenna Observations of the 3c 295 and Boötes Fields: Source Counts and Ultra-Steep Spectrum Sources

Wide-field LOFAR imaging of the field around the double-double radio galaxy B1834+620

The Lockman Hole with LOFAR: Searching for GPS and CSS sources at low frequencies

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