arXiv subjects

N. Oozeer

Publications and source records attributed to N. Oozeer.

23 records · Page 2Linked to original sources

arXiv2016

A KAT-7 view of a low-mass sample of galaxy clusters

Radio observations over the last two decades have provided evidence that diffuse synchrotron emission in the form of megaparsec-scale radio halos in galaxy clusters is likely tracing regions of the intracluster medium where relativistic particles are accelerated during cluster mergers. In this paper we present results of a survey of 14 galaxy clusters carried out with the 7-element Karoo Array Telescope at 1.86 GHz, aimed to extend the current studies of radio halo occurrence to systems with lower masses (M$_{\rm 500} > 4\times10^{14}$ M${_\odot}$). We found upper limits at the $0.6 - 1.9 \times 10^{24}$ Watt Hz$^{-1}$ level for $\sim 50\%$ of the sample, confirming that bright radio halos in less massive galaxy clusters are statistically rare.

astro-ph.CO↗

arXiv2016

A Newly-Discovered Radio Halo in Merging Cluster MACS J2243.3-0935

We report the discovery of a radio halo in the massive merging cluster MACSJ2243.3-0935, as well as a new radio relic candidate, using the Giant Meterwave Radio Telescope and the KAT-7 telescope. The radio halo is coincident with the cluster X-ray emission and has a largest linear scale of approximately 0.9 Mpc. We measure a flux density of $10.0\pm 2.0$ mJy at 610 MHz for the radio halo. We discuss equipartition estimates of the cluster magnetic field and constrain the value to be of the order of 1 $μ$G. The relic candidate is detected at the cluster virial radius where a filament meets the cluster. The relic candidate has a flux density of $5.2\pm 0.8$ mJy at 610 MHz. We discuss possible origins of the relic candidate emission and conclude that the candidate is consistent with an infall relic.

astro-ph.CO↗

arXiv2015

KAT-7 observations of a mass-selected sample of galaxy clusters

The presence of megaparsec-scale radio halos in galaxy clusters has already been established by many observations over the last two decades. The emerging explanation for the formation of these giant sources of diffuse synchrotron radio emission is that they trace turbulent regions in the intracluster medium, where particles are trapped and accelerated during cluster mergers. Our current observational knowledge is, however, mainly limited to massive systems. Here we present observations of a sample of 14 mass-selected galaxy clusters, i.e. $M_{\rm 500} > 4\times10^{14}$~M${_\odot}$, in the Southern Hemisphere, aimed to study the occurrence of radio halos in low mass clusters and test the correlation between the radio halo power at 1.4 GHz $P_{\rm 1.4}$ and the cluster mass $M_{\rm 500}$. Our observations were performed with the 7-element Karoo Array Telescope at 1.86 GHz. We found three candidates to host diffuse cluster-scale emission and derived upper limits at the level of $0.6 - 1.9 \times 10^{24}$~Watt~Hz$^{-1}$ for $\sim 50\%$ of the clusters in the sample, significantly increasing the number of clusters with radio halo information in the considered mass range. Our results confirm that bright radio halos in less massive galaxy clusters are statistically rare.

astro-ph.CO↗

arXiv2015

Discovery of a suspected giant radio galaxy with the KAT-7 array

We detect a new suspected giant radio galaxy (GRG) discovered by KAT-7. The GRG core is identified with the WISE source J013313.50-130330.5, an extragalactic source based on its infrared colors and consistent with a misaligned AGN-type spectrum at $z\approx 0.3$. The multi-$ν$ spectral energy distribution (SED) of the object associated to the GRG core shows a synchrotron peak at $ν\approx 10^{14}$ Hz consistent with the SED of a radio galaxy blazar-like core. The angular size of the lobes are $\sim 4 ^{\prime}$ for the NW lobe and $\sim 1.2 ^{\prime}$ for the SE lobe, corresponding to projected linear distances of $\sim 1078$ kpc and $\sim 324$ kpc, respectively. The best-fit parameters for the SED of the GRG core and the value of jet boosting parameter $δ=2$, indicate that the GRG jet has maximum inclination $θ\approx 30$ deg with respect to the line of sight, a value obtained for $δ=Γ$, while the minimum value of $θ$ is not constrained due to the degeneracy existing with the value of Lorentz factor $Γ$. Given the photometric redshift $z \approx 0.3$, this GRG shows a core luminosity of $P_{1.4 GHz} \approx 5.52 \times 10^{24}$ W Hz$^{-1}$, and a luminosity $P_{1.4 GHz} \approx 1.29 \times 10^{25}$ W Hz$^{-1}$ for the NW lobe and $P_{1.4 GHz} \approx 0.46 \times 10^{25}$ W Hz$^{-1}$ for the SE lobe, consistent with the typical GRG luminosities. The radio lobes show a fractional linear polarization $\approx 9 \%$ consistent with typical values found in other GRG lobes.

astro-ph.GA↗

arXiv2014

Early Science with the Karoo Array Telescope: a Mini-Halo Candidate in Galaxy Cluster Abell 3667

Abell 3667 is among the most well-studied galaxy clusters in the Southern Hemisphere. It is known to host two giant radio relics and a head-tail radio galaxy as the brightest cluster galaxy. Recent work has suggested the additional presence of a bridge of diffuse synchrotron emission connecting the North-Western radio relic with the cluster centre. In this work, we present full-polarization observations of Abell 3667 conducted with the Karoo Array Telescope at 1.33 and 1.82 GHz. Our results show both radio relics as well as the brightest cluster galaxy. We use ancillary higher-resolution data to subtract the emission from this galaxy, revealing a localised excess, which we tentatively identify as a radio mini-halo. This mini-halo candidate has an integrated flux density of $67.2\pm4.9$ mJy beam$^{-1}$ at 1.37 GHz, corresponding to a radio power of P$_{\rm{1.4\,GHz}}=4.28\pm0.31\times10^{23}$ W Hz$^{-1}$, consistent with established trends in mini-halo power scaling.

astro-ph.GA↗