English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Radio halos are faint radio sources usually located at the center of mergingclusters of galaxies. These diffuse radio sources are rare, having so far beenfound only in about 30 clusters of galaxies, suggesting that particularconditions are needed to form and maintain them. It is interesting toinvestigate the presence of radio halos in close pairs of interacting clustersin order to possibly clarify their origin in relation to the evolutionary stateof the merger. In this work, we study the case of the close pair of galaxyclusters A399 and A401. A401 is already known to contain a faint radio halo,while a hint of diffuse emission in A399 has been suggested based on the NVSS.To confirm this possibility, we analyzed deeper Very Large Array observationsat 1.4 GHz of this cluster. We find that the central region of A399 ispermeated by a diffuse low-surface brightness radio emission that we classifyas a radio halo with a linear size of about 570 kpc and a central brightness of0.3 micro-Jy/arcsec^2. Indeed, given their comparatively small projecteddistance of about 3 Mpc, the pair of galaxy clusters A401 and A399 can beconsidered as the first example of double radio halo system. The discovery ofthis double halo is extraordinary given the rarity of these radio sources ingeneral and given that current X-ray data seem to suggest that the two clustersare still in a pre-merger state. Therefore, the origin of the double radio halois likely to be attributed to the individual merging histories of each clusterseparately, rather than to the result of a close encounter between the twosystems.

A double radio halo in the close pair of galaxy clusters Abell 399 and Abell 401