A Radio View of the Bullet Cluster from 100 MHz to 9 GHz

<p>We investigate a sample of 10 massive galaxy clusters for diffuse synchrotron emission. The shortlisted clusters are drawn from a sample of clusters observed with the South Pole Telescope (SPT) shown to have high Sunyaev-Zeldovich (SZ) signals.They are analysed for diffuse emission from the results of the Australia Telescope Compact Array (ATCA) archival data reduction. The focus then is on the cluster with the most prominent diffuse emission - the Bullet cluster. We used the Murchison Widefield Array Commissioning Survey (MWACS) data in conjunction with the ATCA images to derive the spectral behaviour of the Bullet cluster from 0.118 GHz to 8.896 GHz. In particular, we study the spectral properties of the known radio halo and radio relic. We search for spectral bending of this diffuse emission as seen in other clusters like the Coma cluster, A2256, A521 and A3256. We detect the radio relic at all frequencies in the cluster periphery. Polarised flux is detected for the relic at all frequencies except at 1.344 GHz and as expected the percentage polarisation increases with frequency. Our spectral index values of -1.08 ± 0.02 and -1.74 ± 0.22 for 2 regions of the radio relic agreed with the literature. We detect spectral flattening for a region in the radio relic at 4.532 GHz. This is a common spectral characteristic for a radio galaxy. This suggests that the source could be a recently dead radio galaxy. We discuss a scenario in which a dead radio galaxy supplying seed electrons for reacceleration and a merger process providing the required energy for the diffuse radio relic. We detect the radio halo at all frequencies and we derive a spectral index of -2.11±0.03 using our ATCA flux measurements. Our individual flux measurements at 1.344 and 2.1 GHz agree with the literature. However, we get a steeper ATCA spectral index value for the radio halo as compared to the existing value in the literature. We observe spectral flattening of the radio halo in the Bullet cluster at low frequencies between 0.180 GHz and 1.3 GHz. This is similar to the spectral property of the halo in clusters like the Coma cluster, A521 and A3256.</p>

A Radio View of the Bullet Cluster from 100 MHz to 9 GHz

<p>We investigate a sample of 10 massive galaxy clusters for diffuse synchrotron emission. The shortlisted clusters are drawn from a sample of clusters observed with the South Pole Telescope (SPT) shown to have high Sunyaev-Zeldovich (SZ) signals.They are analysed for diffuse emission from the results of the Australia Telescope Compact Array (ATCA) archival data reduction. The focus then is on the cluster with the most prominent diffuse emission - the Bullet cluster. We used the Murchison Widefield Array Commissioning Survey (MWACS) data in conjunction with the ATCA images to derive the spectral behaviour of the Bullet cluster from 0.118 GHz to 8.896 GHz. In particular, we study the spectral properties of the known radio halo and radio relic. We search for spectral bending of this diffuse emission as seen in other clusters like the Coma cluster, A2256, A521 and A3256. We detect the radio relic at all frequencies in the cluster periphery. Polarised flux is detected for the relic at all frequencies except at 1.344 GHz and as expected the percentage polarisation increases with frequency. Our spectral index values of -1.08 ± 0.02 and -1.74 ± 0.22 for 2 regions of the radio relic agreed with the literature. We detect spectral flattening for a region in the radio relic at 4.532 GHz. This is a common spectral characteristic for a radio galaxy. This suggests that the source could be a recently dead radio galaxy. We discuss a scenario in which a dead radio galaxy supplying seed electrons for reacceleration and a merger process providing the required energy for the diffuse radio relic. We detect the radio halo at all frequencies and we derive a spectral index of -2.11±0.03 using our ATCA flux measurements. Our individual flux measurements at 1.344 and 2.1 GHz agree with the literature. However, we get a steeper ATCA spectral index value for the radio halo as compared to the existing value in the literature. We observe spectral flattening of the radio halo in the Bullet cluster at low frequencies between 0.180 GHz and 1.3 GHz. This is similar to the spectral property of the halo in clusters like the Coma cluster, A521 and A3256.</p>

On the Properties of Spectroscopically Confirmed Ultra-diffuse Galaxies across Environments

We present new redshift measurements for 19 candidate ultra-diffuse galaxies (UDGs) from the Systematically Measuring Ultra-Diffuse Galaxies (SMUDGes) survey after conducting a long-slit spectroscopic follow-up campaign on 23 candidates with the Large Binocular Telescope. We combine these results with redshift measurements from other sources for 29 SMUDGes and 20 non-SMUDGes candidate UDGs. Together, this sample yields 44 spectroscopically confirmed UDGs (r e ≥ 1.5 kpc and μ g (0) ≥ 24 mag arcsec−2 within uncertainties) and spans cluster and field environments, with all but one projected on the Coma cluster and environs. We find no statistically significant differences in the structural parameters of cluster and noncluster confirmed UDGs, although there are hints of differences among the axis ratio distributions. Similarly, we find no significant structural differences among those in locally dense or sparse environments. However, we observe a significant difference in color with respect to projected clustercentric radius, confirming trends observed previously in statistical UDG samples. This trend strengthens further when considering whether UDGs reside in either cluster or locally dense environments, suggesting starkly different star formation histories for UDGs residing in high- and low-density environments. Of the 16 large (r e ≥ 3.5 kpc) UDGs in our sample, only one is a field galaxy that falls near the early-type galaxy red sequence. No other field UDGs found in low-density environments fall near the red sequence. This finding, in combination with our detection of Galaxy Evolution Explorer NUV flux in nearly half of the UDGs in sparse environments, suggests that field UDGs are a population of slowly evolving galaxies.

Particle Reacceleration by Turbulence and Radio Constraints on Multimessenger High-energy Emission from the Coma Cluster

Galaxy clusters are considered to be gigantic reservoirs of cosmic rays (CRs). Some of the clusters are found with extended radio emission, which provides evidence for the existence of magnetic fields and CR electrons in the intra-cluster medium. The mechanism of radio halo (RH) emission is still under debate, and it has been believed that turbulent reacceleration plays an important role. In this paper, we study the reacceleration of CR protons and electrons in detail by numerically solving the Fokker–Planck equation, and show how radio and gamma-ray observations can be used to constrain CR distributions and resulting high-energy emission for the Coma cluster. We take into account the radial diffusion of CRs and follow the time evolution of their one-dimensional distribution, by which we investigate the radial profile of the CR injection that is consistent with the observed RH surface brightness. We find that the required injection profile is nontrivial, depending on whether CR electrons have a primary or secondary origin. Although the secondary CR electron scenario predicts larger gamma-ray and neutrino fluxes, it is in tension with the observed RH spectrum for hard injection indexes, α < 2.45. This tension is relaxed if the turbulent diffusion of CRs is much less efficient than the fiducial model, or the reacceleration is more efficient for lower-energy CRs. In both the secondary and primary scenario, we find that galaxy clusters can make a sizable contribution to the all-sky neutrino intensity if the CR energy spectrum is nearly flat.

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.

Non-Keplerian Orbits in Dark Matter

This paper is concerned with the mathematical description of orbits that do not have a constant central gravitating mass. Instead, the attracting mass is a diffuse condensate, a situation which classical orbital dynamics has never encountered before. The famous Coma Cluster of Galaxies is embedded in Dark Matter. Condensed Neutrino Objects (CNO), which are stable assemblages of neutrinos and anti-neutrinos, are candidates for the Dark Matter. A CNO solution has been attained previously for the Coma Cluster, which allows mathematical modeling of galaxy orbital mechanics within Dark Matter, first reported here. For non-zero eccentricity galaxy orbits, each point along the trajectory sees a different gravitating central mass, akin to satellite orbits inside Earth. Mathematically, the galaxy orbits are non-Keplerian, spirographs.