Pilot Study and Early Results of the Cosmic Filaments and Magnetism Survey with Nenufar: The Coma Cluster Field

NenuFAR, the New Extension in Nancay Upgrading LOFAR, is currently in its early science phase. It is in this context that the Cosmic Filaments and Magnetism Pilot Survey is observing sources with the array as it is still under construction—with 57 (56 core, 1 distant) out of a total planned 102 (96 core, 6 distant) mini-arrays online at the time of observation—to get a first look at the low-frequency sky with NenuFAR. One of its targets is the Coma galaxy cluster: a well-known object, host of the prototype radio halo. It also hosts other features of scientific import, including a radio relic, along with a bridge of emission connecting it with the halo. It is thus a well-studied object.In this paper, we show the first confirmed NenuFAR detection of the radio halo and radio relic of the Coma cluster at 34.4 MHz, with associated intrinsic flux density estimates: we find an integrated flux value of 106.3 ± 3.5 Jy for the radio halo, and 102.0 ± 7.4 Jy for the radio relic. These are upper bound values, as they do not include point-source subtraction. We also give an explanation of the technical difficulties encountered in reducing the data, along with steps taken to resolve them. This will be helpful for other scientific projects which will aim to make use of standalone NenuFAR imaging observations in the future.

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LOFAR detection of a low-power radio halo in the galaxy cluster Abell 990

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3581 ◽

2020 ◽

Vol 501 (1) ◽

pp. 576-586

Author(s):

D N Hoang ◽

T W Shimwell ◽

E Osinga ◽

A Bonafede ◽

M Brüggen ◽

...

Keyword(s):

Low Frequency ◽

Galaxy Cluster ◽

Clusters Of Galaxies ◽

Radio Halo ◽

The Galaxy ◽

Major Merger ◽

Murchison Widefield Array ◽

Low X ◽

Massive Clusters ◽

Radio Power

ABSTRACT Radio haloes are extended (∼Mpc), steep spectrum sources found in the central region of dynamically disturbed clusters of galaxies. Only a handful of radio haloes have been reported to reside in galaxy clusters with a mass $M_{500}\lesssim 5\times 10^{14}\, \mathrm{ M}_\odot$. In this paper, we present a LOw Frequency ARray (LOFAR) 144 MHz detection of a radio halo in the galaxy cluster Abell 990 with a mass of $M_{500}=(4.9\pm 0.3)\times 10^{14}\, \mathrm{ M}_\odot$. The halo has a projected size of ${\sim} 700\, {\rm kpc}$ and a flux density of $20.2\pm 2.2\, {\rm mJy}$ or a radio power of $1.2\pm 0.1\times 10^{24}\, {\rm W\, Hz}^{-1}$ at the cluster redshift (z = 0.144) that makes it one of the two haloes with the lowest radio power detected to date. Our analysis of the emission from the cluster with Chandra archival data using dynamical indicators shows that the cluster is not undergoing a major merger but is a slightly disturbed system with a mean temperature of $5\, {\rm keV}$. The low X-ray luminosity of $L_{\mathrm{ X}}=(3.66\pm 0.08)\times 10^{44}\, {\rm erg\, s}^{-1}$ in the 0.1–2.4 keV band implies that the cluster is one of the least luminous systems known to host a radio halo. Our detection of the radio halo in Abell 990 opens the possibility of detecting many more haloes in poorly explored less massive clusters with low-frequency telescopes such as LOFAR, Murchison Widefield Array (MWA, Phase II), and upgraded Giant Metrewave Radio Telescope (uGMRT).

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Reaching thermal noise at ultra-low radio frequencies

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038663 ◽

2020 ◽

Vol 642 ◽

pp. A85 ◽

Cited By ~ 1

Author(s):

F. de Gasperin ◽

G. Brunetti ◽

M. Brüggen ◽

R. van Weeren ◽

W. L. Williams ◽

...

Keyword(s):

Thermal Noise ◽

Signal To Noise Ratio ◽

Low Frequency ◽

Galaxy Cluster ◽

Cosmic Ray ◽

Radio Halo ◽

Cosmic Ray Acceleration ◽

The Galaxy ◽

Background Turbulence ◽

Post Shock

Context. Ultra-low frequency observations (< 100 MHz) are particularly challenging because they are usually performed in a low signal-to-noise ratio regime due to the high sky temperature and because of ionospheric disturbances whose effects are inversely proportional to the observing frequency. Nonetheless, these observations are crucial for studying the emission from low-energy populations of cosmic rays. Aims. We aim to obtain the first thermal-noise limited (∼1.5 mJy beam−1) deep continuum radio map using the Low Frequency Array’s Low Band Antenna (LOFAR LBA) system. Our demonstration observation targeted the galaxy cluster RX J0603.3+4214 (known as the Toothbrush cluster). We used the resulting ultra-low frequency (39–78 MHz) image to study cosmic-ray acceleration and evolution in the post shock region considering the presence of a radio halo. Methods. We describe the data reduction we used to calibrate LOFAR LBA observations. The resulting image was combined with observations at higher frequencies (LOFAR 150 MHz and VLA 1500 MHz) to extract spectral information. Results. We obtained the first thermal-noise limited image from an observation carried out with the LOFAR LBA system using all Dutch stations at a central frequency of 58 MHz. With eight hours of data, we reached an rms noise of 1.3 mJy beam−1 at a resolution of 18″ × 11″. Conclusions. The procedure we developed is an important step towards routine high-fidelity imaging with the LOFAR LBA. The analysis of the radio spectra shows that the radio relic extends to distances of 800 kpc downstream from the shock front, larger than what is allowed by electron cooling time. Furthermore, the shock wave started accelerating electrons already at a projected distance of < 300 kpc from the crossing point of the two clusters. These results may be explained by electrons being re-accelerated downstream by background turbulence, possibly combined with projection effects with respect to the radio halo.

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Diffuse radio emission in the galaxy cluster SPT-CL J2031−4037: a steep-spectrum intermediate radio halo?

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slaa002 ◽

2020 ◽

Vol 493 (1) ◽

pp. L28-L32 ◽

Cited By ~ 1

Author(s):

Ramij Raja ◽

Majidul Rahaman ◽

Abhirup Datta ◽

Jack O Burns ◽

H T Intema ◽

...

Keyword(s):

Radio Emission ◽

Spectral Index ◽

Low Frequency ◽

Galaxy Cluster ◽

Transition System ◽

Cluster Galaxy ◽

Radio Halo ◽

Spectrum Radio ◽

Upper Limits ◽

The Galaxy

ABSTRACT The advent of sensitive low-frequency radio observations has revealed a number of diffuse radio objects with peculiar properties that are challenging our understanding of the physics of the intracluster medium. Here, we report the discovery of a steep-spectrum radio halo surrounding the central brightest cluster galaxy (BCG) in the galaxy cluster SPT-CL J2031−4037. This cluster is morphologically disturbed yet has a weak cool core, an example of a cool-core/non-cool-core transition system, which harbours a radio halo ∼0.7 Mpc in size. The halo emission detected at 1.7 GHz is less extended compared to that in the 325 MHz observation, and the spectral index of the part of the halo visible at the 325 MHz to 1.7 GHz frequencies was found to be −1.35 ± 0.07. Also, P1.4 GHz was found to be 0.77 × 1024 W Hz−1, which falls in the region where radio mini-haloes, halo upper limits and ultra-steep-spectrum (USS) haloes are found in the P1.4 GHz–LX plane. Additionally, simulations presented in the paper provide support for the scenario of the steep spectrum. The diffuse radio emission found in this cluster may be a steep-spectrum ‘intermediate’ or ‘hybrid’ radio halo that is transitioning into a mini-halo.

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Ultra-steep spectrum emission in the merging galaxy cluster Abell 1914

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833992 ◽

2019 ◽

Vol 622 ◽

pp. A22 ◽

Cited By ~ 6

Author(s):

S. Mandal ◽

H. T. Intema ◽

T. W. Shimwell ◽

R. J. van Weeren ◽

A. Botteon ◽

...

Keyword(s):

Low Frequency ◽

Galaxy Cluster ◽

Diffuse Emission ◽

Radio Observations ◽

Very Large Array ◽

Radio Halo ◽

The Galaxy ◽

Distinct Source ◽

Relativistic Particles ◽

Massive Galaxy

A number of radio observations have revealed the presence of large synchrotron-emitting sources associated with the intra-cluster medium. There is strong observational evidence that the emitting particles have been (re-)accelerated by shocks and turbulence generated during merger events. The particles that are accelerated are thought to have higher initial energies than those in the thermal pool but the origin of such mildly relativistic particles remains uncertain and needs to be further investigated. The galaxy cluster Abell 1914 is a massive galaxy cluster in which X-ray observations show clear evidence of merging activity. We carried out radio observations of this cluster with the LOw Frequency ARay (LOFAR) at 150 MHz and the Giant Metrewave Radio Telescope (GMRT) at 610 MHz. We also analysed Very Large Array (VLA) 1.4 GHz data, archival GMRT 325 MHz data, CFHT weak lensing data and Chandra observations. Our analysis shows that the ultra-steep spectrum source (4C38.39; α ≲ −2), previously thought to be part of a radio halo, is a distinct source with properties that are consistent with revived fossil plasma sources. Finally, we detect some diffuse emission to the west of the source 4C38.39 that could belong to a radio halo.

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A Hidden Radio Halo in the Galaxy Cluster A 1682?

Journal of Astrophysics and Astronomy ◽

10.1007/s12036-011-9097-1 ◽

2011 ◽

Vol 32 (4) ◽

pp. 501-504 ◽

Cited By ~ 1

Author(s):

T. Venturi ◽

S. Giacintucci ◽

D. Dallacasa

Keyword(s):

Galaxy Cluster ◽

Radio Halo ◽

The Galaxy ◽

Cluster A

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Characterizing the radio emission from the binary galaxy cluster merger Abell 2146

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834025 ◽

2019 ◽

Vol 622 ◽

pp. A21 ◽

Cited By ~ 4

Author(s):

D. N. Hoang ◽

T. W. Shimwell ◽

R. J. van Weeren ◽

H. J. A. Röttgering ◽

A. Botteon ◽

...

Keyword(s):

Particle Acceleration ◽

Radio Emission ◽

Low Frequency ◽

Galaxy Cluster ◽

Relativistic Electrons ◽

Extended Source ◽

Very Large Array ◽

Radio Halo ◽

Extended Radio ◽

Relativistic Particles

Context. Collisions of galaxy clusters generate shocks and turbulence in the intra-cluster medium (ICM). The presence of relativistic particles and magnetic fields is inferred through the detection of extended synchrotron radio sources such as haloes and relics and implies that merger shocks and turbulence are capable of (re-)accelerating particles to relativistic energies. However, the precise relationship between merger shocks, turbulence, and extended radio emission is still unclear. Studies of the most simple binary cluster mergers are important to help understand the particle acceleration in the ICM. Aims. Our main aim is to study the properties of the extended radio emission and particle acceleration mechanism(s) associated with the generation of relativistic particles in the ICM. Methods. We measure the low-frequency radio emission from the merging galaxy cluster Abell 2146 with LOFAR at 144 MHz. We characterize the spectral properties of the radio emission by combining these data with data from archival Giant Metrewave Radio Telescope (GMRT) at 238 MHz and 612 MHz and Very Large Array (VLA) at 1.5 GHz. Results. We observe extended radio emission at 144 MHz behind the NW and SE shocks. Across the NW extended source, the spectral index steepens from −1.06 ± 0.06 to −1.29 ± 0.09 in the direction of the cluster centre. This spectral behaviour suggests that a relic is associated with the NW upstream shock. The precise nature of the SE extended emission is unclear. It may be a radio halo bounded by a shock or a superposition of a relic and halo. At 144 MHz, we detect a faint emission that was not seen with high-frequency observations, implying a steep (α < −1.3) spectrum nature of the bridge emission. Conclusions. Our results imply that the extended radio emission in Abell 2146 is probably associated with shocks and turbulence during cluster merger. The relativistic electrons in the NW and SE may originate from fossil plasma and thermal electrons, respectively.

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Deep low frequency image of Coma cluster of galaxies

2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) ◽

10.23919/ursiap-rasc.2019.8738415 ◽

2019 ◽

Author(s):

Dharam V Lal ◽

C.H. Ishwara-Chandra

Keyword(s):

Low Frequency ◽

Coma Cluster ◽

Cluster Of Galaxies

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Stellar feedback in dwarf irregular galaxies with radio continuum observations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318006841 ◽

2018 ◽

Vol 14 (S344) ◽

pp. 255-258

Author(s):

Volker Heesen ◽

Aritra Basu ◽

Elias Brinks ◽

George Heald ◽

Andrew Fletcher ◽

...

Keyword(s):

Star Formation ◽

Low Frequency ◽

Cosmic Ray ◽

Radio Continuum ◽

Very Large Array ◽

Radio Halo ◽

Spatially Resolved ◽

Ic 10 ◽

Irregular Galaxies ◽

Dwarf Irregular Galaxies

AbstractLow-mass dwarf irregular galaxies are subject to outflows, in which cosmic rays may play a very important role; they can be traced via their electron component, the cosmic ray electrons (CRe), in the radio continuum as non-thermal synchrotron emission. With the advent of sensitive low-frequency observations, such as with the Low-Frequency Array (LOFAR), we can trace CRe far away from star formation sites. Together with GHz-observations, such as with the Very Large Array (VLA), we can study spatially resolved radio continuum spectra at matched angular resolution and sensitivity. Here, we present results from our 6-GHz VLA survey of 40 nearby dwarf galaxies and our LOFAR study of the nearby starburst dwarf irregular galaxy IC 10. We explore the relation of RC emission with star formation tracers and study in IC 10 the nature of a low-frequency radio halo, which we find to be the result of a galactic wind.

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Spatially resolved studies of extragalactic jets in high redshift radio galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315002239 ◽

2014 ◽

Vol 10 (S313) ◽

pp. 231-235

Author(s):

Leah K. Morabito ◽

Adam Deller ◽

J. B. R. Oonk ◽

Huub Röttgering ◽

George Miley

Keyword(s):

High Redshift ◽

Low Frequency ◽

Radio Galaxies ◽

Radio Sources ◽

Spatially Resolved ◽

Long Baseline ◽

Early Results ◽

Spectrum Radio ◽

Extragalactic Jets ◽

Frequency Survey

AbstractThe correlation between radio spectral steepness and redshift has been successfully used to find high redshift (z ⩾ 2) radio galaxies, but the origin of this relation is unknown. The ultra-steep spectra of high-z radio sources make them ideally suited for studies with the Low Band Antenna of the new Low Frequency Array, which covers 10–80 MHz and has baselines up to about 1300 km. As part of an ongoing survey, we use the longest baselines to map the low-frequency (< 70 MHz) spatial distributions along the jets of 5 bright extended steep spectrum high-z radio sources. From this, we will determine whether the spectra change over these spatially resolved sources, thereby constraining particle acceleration processes. We present early results from our low-frequency survey of ultra-steep spectrum radio galaxies. The first low frequency long baseline images of these objects are presented.

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