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

Mahony, E. K.; Morganti, Raffaella; Prandoni, I.; Bemmel, I. van

doi:10.1002/asna.201512279

Cited by 27 publications

(40 citation statements)

References 29 publications

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“…Prandoni et al 2018 for an overview). In particular, this is one of the fields for which there exist deep Low Frequency Array (LOFAR, van Haarlem et al 2013) observations covering ∼30 deg 2 (Mahony et al 2016;Mandal et al, in prep. ;Tasse et al, in prep.).…”

Section: Lockman Hole Datamentioning

confidence: 99%

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The life cycle of radio galaxies in the LOFAR Lockman Hole field

Jurlin

Morganti

Brienza

et al. 2020

A&A

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116

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Radio galaxies are known to go through cycles of activity, where phases of apparent quiescence can be followed by repeated activity of the central supermassive black hole. A better understanding of this cycle is crucial for ascertaining the energetic impact that the jets have on the host galaxy, but little is known about it. We used deep LOFAR images at 150 MHz of the Lockman Hole extragalactic field to select a sample of 158 radio sources with sizes > 60″ in different phases of their jet life cycle. Using a variety of criteria (e.g. core prominence combined with low-surface brightness of the extended emission and steep spectrum of the central region) we selected a subsample of candidate restarted radio galaxies representing between 13% and 15% of the 158 sources of the main sample. We compare their properties to the rest of the sample, which consists of remnant candidates and active radio galaxies. Optical identifications and characterisations of the host galaxies indicate similar properties for candidate restarted, remnant, and active radio galaxies, suggesting that they all come from the same parent population. The fraction of restarted radio galaxies is slightly higher with respect to remnants, suggesting that the restarted phase can often follow after a relatively short remnant phase (the duration of the remnant phase being a few times 107 years). This confirms that the remnant and restarted phases are integral parts of the life cycle of massive elliptical galaxies. A preliminary investigation does not suggest a strong dependence of this cycle on the environment surrounding any given galaxy.

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Section: Lockman Hole Datamentioning

confidence: 99%

“…For this work we used the published image and catalogue at 150 MHz presented by Mahony et al (2016) with a resolution of 18 and reaching a noise level of rms = 150 µJy beam −1 . In addition, we used a newly available and deeper high-resolution image presented by Mandal et al (in prep.…”

Section: Lockman Hole Datamentioning

confidence: 99%

The life cycle of radio galaxies in the LOFAR Lockman Hole field

Jurlin

Morganti

Brienza

et al. 2020

A&A

Self Cite

116

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“…In addition, repeat multi-frequency radio observations would confirm these sources as intrinsically peaked and limit the number of vari-able sources erroneously classified as peaked spectrum. A preliminary analysis of GPS and CSS sources in the Lockman Hole is also presented in Mahony et al (2016).…”

Section: Peaked-spectrum Sourcesmentioning

confidence: 99%

The Lockman Hole project: LOFAR observations and spectral index properties of low-frequency radio sources

Mahony¹,

Morganti²,

Prandoni³

et al. 2016

Monthly Notices of the Royal Astronomical Society

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The Lockman Hole is a well-studied extragalactic field with extensive multi-band ancillary data covering a wide range in frequency, essential for characterising the physical and evolutionary properties of the various source populations detected in deep radio fields (mainly star-forming galaxies and AGNs). In this paper we present new 150-MHz observations carried out with the LOw Frequency ARray (LOFAR), allowing us to explore a new spectral window for the faint radio source population. This 150-MHz image covers an area of 34.7 square degrees with a resolution of 18.6×14.7 arcsec and reaches an rms of 160 µJy beam −1 at the centre of the field.As expected for a low-frequency selected sample, the vast majority of sources exhibit steep spectra, with a median spectral index of α 1400 150 = −0.78 ± 0.015. The median spectral index becomes slightly flatter (increasing from α 1400 150 = −0.84 to α 1400 150 = −0.75) with decreasing flux density down to S 150 ∼10 mJy before flattening out and remaining constant below this flux level. For a bright subset of the 150-MHz selected sample we can trace the spectral properties down to lower frequencies using 60-MHz LOFAR observations, finding tentative evidence for sources to become flatter in spectrum between 60 and 150 MHz. Using the deep, multi-frequency data available in the Lockman Hole, we identify a sample of 100 Ultra-steep spectrum (USS) sources and 13 peaked spectrum sources. We estimate that up to 21 per cent of these could have z > 4 and are candidate high-z radio galaxies, but further follow-up observations are required to confirm the physical nature of these objects.

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“…With new low-frequency radio interferometer arrays such as the Low Frequency Array (LOFAR;van Haarlem et al 2013), the Murchison Widefield Array (MWA; Bowman et al 2013;Tingay et al 2013) and the Giant Metrewave Radio Telescope (GMRT; Swarup et al 1991) we are able to move towards lower radio frequencies, at which the effects of Doppler boosting can be minimised. A number of LOFAR surveys have been carried out over specific fields such as the Lockman hole field (Mahony et al 2016), the Boötes field (Williams et al 2016), and the Herschel-Astrophysical Terahertz Large Area Survey/North Galactic Pole field (H-ATLAS/NGP; Hardcastle et al 2016). Recently, LOFAR has started observing the northern sky as part of the LOFAR Twometre Sky Survey (LoTSS; Shimwell et al 2017), which provides unprecedented sensitivity (∼70 µJy beam −1 ) with a resolution of 6 arcsec; for optically thin synchrotron emission LoTSS is ten times deeper than the FIRST survey (assuming α = 0.7) and is also sensitive to extended emission that is invisible to FIRST.…”

Section: Introductionmentioning

confidence: 99%

LoTSS/HETDEX: Optical quasars

Gürkan

Hardcastle

Best

et al. 2019

A&A

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The radio-loud/radio-quiet (RL/RQ) dichotomy in quasars is still an open question. Although it is thought that accretion onto supermassive black holes in the centre the host galaxies of quasars is responsible for some radio continuum emission, there is still a debate as to whether star formation or active galactic nuclei (AGN) activity dominate the radio continuum luminosity. To date, radio emission in quasars has been investigated almost exclusively using high-frequency observations in which the Doppler boosting might have an important effect on the measured radio luminosity, whereas extended structures, best observed at low radio frequencies, are not affected by the Doppler enhancement. We used a sample of quasars selected by their optical spectra in conjunction with sensitive and high-resolution low-frequency radio data provided by the LOw Frequency ARray (LOFAR) as part of the LOFAR Two-Metre Sky Survey (LoTSS) to investigate their radio properties using the radio loudness parameter (R =L144 MHz/Li band). The examination of the radio continuum emission and RL/RQ dichotomy in quasars exhibits that quasars show a wide continuum of radio properties (i.e. no clear bimodality in the distribution of ℛ). Radio continuum emission at low frequencies in low-luminosity quasars is consistent with being dominated by star formation. We see a significant albeit weak dependency of ℛ on the source nuclear parameters. For the first time, we are able to resolve radio morphologies of a considerable number of quasars. All these crucial results highlight the impact of the deep and high-resolution low-frequency radio surveys that foreshadow the compelling science cases for the Square Kilometre Array (SKA).

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

Cited by 27 publications

References 29 publications

The life cycle of radio galaxies in the LOFAR Lockman Hole field

The life cycle of radio galaxies in the LOFAR Lockman Hole field

The Lockman Hole project: LOFAR observations and spectral index properties of low-frequency radio sources

LoTSS/HETDEX: Optical quasars

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