LOFAR Discovery of a Radio Halo in the High-redshift Galaxy Cluster PSZ2 G099.86+58.45

Journal
Date Issued
2019
Author(s)
•
•
Di Gennaro, G.
•
•
•
Shimwell, T. W.
•
van Weeren, R. J.
•
Brüggen, M.
•
•
Izzo, L.
•
Bîrzan, L.
•
•
Cuciti, V.
•
•
Röttgering, H. J. A.
•
Hardcastle, M.
•
Mechev, A. P.
•
Tasse, C.
DOI
Abstract
In this Letter, we report the discovery of a radio halo in the high-redshift galaxy cluster PSZ2 G099.86+58.45 (z = 0.616) with the LOw Frequency ARray (LOFAR) at 120-168 MHz. This is one of the most distant radio halos discovered so far. The diffuse emission extends over ∼1 Mpc and has a morphology similar to that of the X-ray emission as revealed by XMM-Newton data. The halo is very faint at higher frequencies and is barely detected by follow-up 1-2 GHz Karl G. Jansky Very Large Array observations, which enable us to constrain the radio spectral index to be α ≲ 1.5-1.6, i.e., with properties between canonical and ultra-steep spectrum radio halos. Radio halos are currently explained as synchrotron radiation from relativistic electrons that are re-accelerated in the intracluster medium by turbulence driven by energetic mergers. We show that in such a framework radio halos are expected to be relatively common at ∼150 MHz (∼30%-60%) in clusters with mass and redshift similar to PSZ2 G099.86+58.45; however, at least two-thirds of these radio halos should have a steep spectrum and thus be very faint above ∼1 GHz frequencies. Furthermore, because the luminosity of radio halos at high redshift depends strongly on the magnetic field strength in the hosting clusters, future LOFAR observations will also provide vital information on the origin and amplification of magnetic fields in galaxy clusters.
Volume
881
Issue
1
Start page
L18
Uri
Url
Issn Identifier
2041-8205
Ads BibCode
2019ApJ...881L..18C
Rights
open.access
File(s)
Loading...
Thumbnail Image
Name

Cassano_2019_ApJL_881_L18.pdf

Description
Pdf editoriale
Size

1.47 MB

Format

Adobe PDF

Checksum (MD5)

7ee68ba8955b3a87d6d0bfd19f37d529