Sunyaev Zel’dovich high resolution view of filamentary structures between galaxy clusters pairs

¹ Sapienza University of Rome, Physics Department, Piazzale Aldo Moro 5, 00185 Rome, Italy
² INFN - Sezione di Roma, Piazzale Aldo Moro 5 - I-00185, Rome, Italy

^* e-mail: federico.radiconi@roma1.infn.it

Published online: 17 January 2022

Abstract

Strong observational and theoretical evidences suggest that about half of the baryons in the Universe should lie outside galaxy clusters in a lowdensity and hot phase in filaments connecting galaxy clusters. Due to the low density, most of this filamentary plasma can not be detected by X-ray observatories. In particular cases of low redshift cluster pairs in the pre-merging phase, the Sunyaev Zel’dovich (SZ) effect can be used to observe the intercluster regions and detect the imprint of missing baryons.

The Abell 399-401 (A399-401) system is the perfect laboratory to test our ability to detect filamentary structures via the SZ effect with <~ 1′ angular resolution. This pair has been well studied at several frequencies: it exhibits double radio-halos, an excess of X-ray emission in the intercluster region and a synchrotron radio ‘ridge’ connecting the two clusters. Moreover the Planck satellite provided the first SZ detection of the gas between A399-401 despite the poor angular resolution (~ 10′) of its SZ map.

We have used an Atacama Cosmology Telescope (ACT) and Planck satellite Compton-y map (1:65′ angular resolution) that combines ACT data from 2008 to 2019 with Planck maps to study the A399-401 system in detail. We present the data analysis and results.