The Very Large Array Low-frequency Sky Survey Redux (VLSSr)

Lane, W. M.; Cotton, W. D.; Velzen, S. van; Clarke, T. E.; Kassim, N. E.; Helmboldt, J. F.; Lazio, T. Joseph W.; Cohen, A. S.

doi:10.1093/mnras/stu256

Cited by 254 publications

(229 citation statements)

References 34 publications

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“…We analyzed the images obtained from the VLA LowFrequency Sky Survey redux (VLSSr at 74 MHz; Lane et al 2014), the VLA archive data in P-Band (330 MHz), the VLA archive data in L-Band (1443 and 1630 MHz), and the SRT (6600 MHz) data. We smoothed all the images to the same resolution as that of the SRT image (see top panels of Fig.…”

Section: Spectral Aging Analysismentioning

confidence: 99%

Sardinia Radio Telescope observations of Abell 194

Govoni

Murgia

Vacca

et al. 2017

A&A

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Aims. We study the intra-cluster magnetic field in the poor galaxy cluster Abell 194 by complementing radio data, at different frequencies, with data in the optical and X-ray bands. Methods. We analyze new total intensity and polarization observations of Abell 194 obtained with the Sardinia Radio Telescope (SRT). We use the SRT data in combination with archival Very Large Array observations to derive both the spectral aging and Rotation Measure (RM) images of the radio galaxies 3C 40A and 3C 40B embedded in Abell 194. To obtain new additional insights in the cluster structure we investigate the redshifts of 1893 galaxies, resulting in a sample of 143 fiducial cluster members. We analyze the available ROSAT and Chandra observations to measure the electron density profile of the galaxy cluster.Results. The optical analysis indicates that Abell 194 does not show a major and recent cluster merger, but rather agrees with a scenario of accretion of small groups, mainly along the NE-SW direction. Under the minimum energy assumption, the lifetimes of synchrotron electrons in 3C40 B measured from the spectral break are found to be 157±11 Myrs. The break frequency image and the electron density profile inferred from the X-ray emission are used in combination with the RM data to constrain the intra-cluster magnetic field power spectrum. By assuming a Kolmogorov power law power spectrum with a minimum scale of fluctuations of Λ min = 1 kpc, we find that the RM data in Abell 194 are well described by a magnetic field with a maximum scale of fluctuations of Λ max = (64 ± 24) kpc. We find a central magnetic field strength of B 0 = (1.5 ± 0.2) µG, the lowest ever measured so far in galaxy clusters based on Faraday rotation analysis. Further out, the field decreases with the radius following the gas density to the power of η=1.1±0.2. Comparing Abell 194 with a small sample of galaxy clusters, there is a hint of a trend between central electron densities and magnetic field strengths.

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Section: Spectral Aging Analysismentioning

confidence: 99%

Sardinia Radio Telescope observations of Abell 194

Govoni

Murgia

Vacca

et al. 2017

A&A

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“…The P cav literature values we use for the correlation studies are summarized in Section 2.5. We do not include the VLA Low-Frequency Sky Survey Redux at 74 MHz (VLSSr; Cohen et al 2007;Lane et al 2012Lane et al , 2014 in our analysis due to its low sensitivity combined with low resolution and insufficient sky coverage (see Section 2.6). The Galactic and Extragalactic Allsky Murchison Widefield Array survey (GLEAM; Wayth et al 2015;Hurley-Walker et al 2017) was released shortly before the submission of this work and we do not include it in our study.…”

Section: Data Sources and Sample Selectionmentioning

confidence: 99%

LOFAR MSSS: The scaling relation between AGN cavity power and radio luminosity at low radio frequencies

Kokotanekov

Wise

Heald

et al. 2017

A&A

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We present a new analysis of the widely used relation between cavity power and radio luminosity in clusters of galaxies with evidence for strong AGN feedback. We study the correlation at low radio frequencies using two new surveys -the First Alternative Data Release of the TIFR GMRT Sky Survey (TGSS ADR1) at 148 MHz and LOFAR's first all-sky survey, the Multifrequency Snapshot Sky Survey (MSSS) at 140 MHz. We find a scaling relation P cav ∝ L β 148 , with a logarithmic slope of β = 0.51 ± 0.14, which is in good agreement with previous results based on data at 327 MHz. The large scatter present in this correlation confirms the conclusion reached at higher frequencies that the total radio luminosity at a single frequency is a poor predictor of the total jet power. Previous studies have shown that the magnitude of this scatter can be reduced when bolometric radio luminosity corrected for spectral aging is used. We show that including additional measurements at 148 MHz alone is insufficient to improve this correction and further reduce the scatter in the correlation. For a subset of four well-resolved sources, we examine the detected extended structures at low frequencies and compare with the morphology known from higher frequency images and Chandra X-ray maps. In Perseus we discuss details in the structures of the radio mini-halo, while in the 2A 0335+096 cluster we observe new diffuse emission associated with multiple X-ray cavities and likely originating from past activity. For A2199 and MS 0735.6+7421, we confirm that the observed low-frequency radio lobes are confined to the extents known from higher frequencies. This new low-frequency analysis highlights the fact that existing cavity power to radio luminosity relations are based on a relatively narrow range of AGN outburst ages. We discuss how the correlation could be extended using low frequency data from the LOFAR Two-metre Sky Survey (LoTSS) in combination with future, complementary deeper X-ray observations.

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“…These blocks were then phase calibrated using the preliminary LOFAR global sky model. This global sky model consists of positions of sources from the NRAO VLA Sky Survey (NVSS) catalogue (Condon et al 1998) with fluxes obtained from a power-law spectral fitting with data from the NVSS, the Westerbork Northern Sky Survey (WENSS; Rengelink et al 1997) and the VLA Low-Frequency Sky Survey redux (VLSSr; Cohen et al 2007) (Lane et al 2014) surveys.…”

Section: Initial Calibrationmentioning

confidence: 99%

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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The Very Large Array Low-frequency Sky Survey Redux (VLSSr)

Cited by 254 publications

References 34 publications

Sardinia Radio Telescope observations of Abell 194

Sardinia Radio Telescope observations of Abell 194

LOFAR MSSS: The scaling relation between AGN cavity power and radio luminosity at low radio frequencies

The nature of the low-frequency emission of M 51

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