scholarly journals Spectral Index of the Filaments in the Abell 523 Radio Halo

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 112
Author(s):  
Valentina Vacca ◽  
Federica Govoni ◽  
Richard A. Perley ◽  
Matteo Murgia ◽  
Ettore Carretti ◽  
...  
Keyword(s):  
Spectral Index ◽  
Galaxy Cluster ◽  
Large Array ◽  
Spectral Indices ◽  
Very Large Array ◽  
Radio Halo ◽  
Highly Efficient ◽  
The Galaxy

The galaxy cluster Abell 523 hosts a radio halo characterized by the presence of two filaments transversely located with respect to the cluster merger axis. In this paper, we present a spectral index image of these filaments between 1.410 and 1.782 GHz obtained with Jansky Very Large Array observations. We find a steepening of the spectral index of the filaments at frequencies ≳1.4 GHz and an indication that bright patches are characterized by flat spectral indices. Our results are consistent with a scenario of highly-efficient turbulence induced by merger phenomena.

Bipolar outflow of gas in the spiral galaxy NGC 3079

1986 ◽  
Vol 64 (4) ◽  
pp. 531-535 ◽  
Author(s):  
Nebojsa Duric ◽  
E. R. Seaquist
Keyword(s):  
Spectral Index ◽  
Spiral Galaxy ◽  
Central Region ◽  
Qualitative Description ◽  
Radio Continuum ◽  
Large Array ◽  
Very Large Array ◽  
Bipolar Outflow ◽  
The Galaxy

Very large array, radio-continuum observations of the edge-on spiral galaxy NGC 3079 are presented. The observations reveal that the nucleus has windlike properties and that the central region of the galaxy exhibits an unusual figure-eight morphology that shows evidence of severe depolarization and a flattening spectral index away from the nucleus. A qualitative description of a model is presented to account for the observed radio properties. It is shown that a wind-driven shock propagating away from the nucleus and focused by the ambient disk gas can give rise to the observed morphology.

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

2020 ◽  
Vol 493 (1) ◽  
pp. L28-L32 ◽  
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.

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

2019 ◽  
Vol 622 ◽  
pp. A22 ◽  
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.

scholarly journals Hunting dark matter in galaxy clusters with non-thermal electrons

2020 ◽  
Vol 494 (1) ◽  
pp. 1128-1132
Author(s):  
Geoff Beck
Keyword(s):  
Dark Matter ◽  
Power Law ◽  
Electron Spectrum ◽  
Electron Distribution ◽  
Indirect Comparison ◽  
Galaxy Cluster ◽  
Large Array ◽  
Electron Population ◽  
Very Large Array ◽  
Hard Power

ABSTRACT The electron population inferred to be responsible for the mini-halo within the Ophiuchus galaxy cluster is a steep power law in energy with a slope of 3.8. This is substantially different to that predicted by dark matter (DM) annihilation models. In this work, we present a method of indirect comparison between the observed electron spectrum and that predicted for indirect DM emissions. This method utilizes differences in the consequences of a given electron distribution on the subsequent spectral features of synchrotron emissions. To fully exploit this difference, by leveraging the fact that the peak and cut-off synchrotron frequencies are substantially different to hard power-law cases for WIMP masses above ∼50 GeV, we find that we need μJy sensitivities at frequencies above 10 GHz while being sensitive to arcminute scales. We explore the extent to which this electron spectrum comparison can be validated with the up-coming next-generation Very Large Array (ngVLA) instrument. We show that, with the ngVLA, this method allows us to produce far stronger constraints than existing VLA data, indeed these exceed the Fermi-LAT dwarf searches in a wide variety of annihilation channels and for all studied magnetic field scenarios.

scholarly journals Jansky VLA S-band view of Hα emitters (HAEs) associated with a protocluster 4C23.56 at z = 2.5

2014 ◽  
Vol 10 (S309) ◽  
pp. 287-288
Author(s):  
Minju Lee ◽  
Kenta Suzuki ◽  
Kotaro Kohno ◽  
Yoichi Tamura ◽  
Daisuke Iono ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Narrow Band ◽  
Narrow Band Imaging ◽  
Large Array ◽  
Dense Region ◽  
Very Large Array ◽  
Star Forming ◽  
Dust Extinction ◽  
The Galaxy ◽  
Galaxy Populations

AbstractWe present recent results on Karl Jansky Very Large Array (JVLA) deep S-band (2-4 GHz) observation towards a protocluster 4C23.56 at redshift z ∼ 2.5. The protocluster 4C23.56 is known to have a significant over density (∼ 5 times) of star-burst galaxies selected to be Hα line-bright by a Subaru narrow band imaging. Now we have found 25 HAEs associated with the protocluster. These starburst HAEs are likely to become massive ellipticals at z = 0 in a cluster. Various other galaxy populations also reside in this field and the fact makes the field very unique as a tool to understand galaxy formation in a over dense region. Subsequent deep 1100-μm continuum surveys by the ASTE 10-m dish have discovered that several submillimeter bright galaxies (SMGs) coincide with HAEs, suggesting HAEs undergoing dusty starbursts. As star formation rates (SFRs) of HAEs might have been underestimated, we use radio being resistant to dust extinction. We investigate the correlation between SFR1.4 GHz and SFRHα for radio index α = 0.8 to see if the correlation holds for the sources and to check the number of dusty star forming galaxies. Our final results will allow us to evaluate quantitatively how the galaxy formation channel may be different under the condition of over-densities.

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

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).

scholarly journals Reaching thermal noise at ultra-low radio frequencies

2020 ◽  
Vol 642 ◽  
pp. A85 ◽  
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.

scholarly journals A radio halo surrounding the Brightest Cluster Galaxy in RXCJ0232.2–4420: a mini-halo in transition?

2019 ◽  
Vol 486 (1) ◽  
pp. L80-L84 ◽  
Author(s):  
Ruta Kale ◽  
Krishna M Shende ◽  
Viral Parekh
Keyword(s):  
Radio Source ◽  
Surface Brightness ◽  
Galaxy Cluster ◽  
Cosmic Ray ◽  
Radio Sources ◽  
Cluster Galaxy ◽  
X Ray ◽  
Radio Halo ◽  
The Galaxy ◽  
Radio Power

ABSTRACT Diffuse radio sources associated with the intra-cluster medium are direct probes of the cosmic ray electrons and magnetic fields. We report the discovery of a diffuse radio source in the galaxy cluster RXCJ0232.2–4420 (SPT-CL J0232–4421, z = 0.2836) using 606 MHz observations with the Giant Metrewave Radio Telescope. The diffuse radio source surrounds the Brightest Cluster Galaxy in the cluster-like typical radio mini-haloes. However the total extent of it is 550 × 800 kpc2, which is larger than mini-haloes and similar to that of radio haloes. The BCG itself is also a radio source with a marginally resolved core at 7 arcsec (30 kpc) resolution. We measure the 606 MHz flux density of the RH to be 52 ± 5 mJy. Assuming a spectral index of 1.3, the 1.4 GHz radio power is 4.5 × 1024 W Hz−1. The dynamical state of the cluster has been inferred to be 'relaxed’ and also as 'complex’, depending on the classification methods based on the morphology of the X-ray surface brightness. This system thus seems to be in the transition phase from a mini-halo to a radio halo.

scholarly journals Magnetic-Field Vector Maps of Nearby Spiral Galaxies

Galaxies ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 32 ◽  
Author(s):  
Hiroyuki Nakanishi ◽  
Kohei Kurahara ◽  
Kenta Anraku
Keyword(s):  
Magnetic Field ◽  
Spiral Galaxies ◽  
Transverse Magnetic ◽  
Field Vector ◽  
Line Of Sight ◽  
Large Array ◽  
Magnetic Vector ◽  
Very Large Array ◽  
Rotation Measure ◽  
The Galaxy

We present a method for determining the directions of magnetic-field vectors in a spiral galaxy using two synchrotron polarization maps, an optical image, and a velocity field. The orientation of the transverse magnetic field is determined with a synchrotron polarization map of a higher-frequency band, and the 180 ∘ -ambiguity is solved by using a sign of Rotation Measure (RM) after determining the geometrical orientation of a disk based on an assumption of trailing spiral arms. The advantage of this method is that the direction of a magnetic vector for each line of sight throughout the galaxy can inexpensively be determined, with easily available data and simple assumptions. We applied this method to three nearby spiral galaxies using archival data obtained with a Very Large Array (VLA) to demonstrate how it works. The three galaxies have both clockwise and counterclockwise magnetic fields, which implies that none of the three galaxies is classified in a simple Axis-Symmetric type, but types of higher modes, and that magnetic reversals commonly exist.

Sign in / Sign up

Export Citation Format

Share Document