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Revealing the origin of ORCs with LEM: A lucky CLOVERLEAF at z~0.045

Presentation #110.12 in the session LEM.

Published onJul 01, 2023
Revealing the origin of ORCs with LEM: A lucky CLOVERLEAF at z~0.045

Odd radio circles (ORCs) are a newly discovered class of radio sources, first detected by Norris et al. (2021) with the Australian SKA Pathfinder (ASKAP) and GMRT surveys and recently also found in the MeerKAT Galaxy Cluster Legacy Survey (Lochner et al. 2022). They are complex, often ring like structures spanning several hundreds of kpc diameter around early type galaxies with stellar masses of several times 1011 solar masses. They are thought to be caused by shocks within the CGM residing around the virial radius, traced by the shock accelerated electrons producing synchrotron emission within magnetic fields penetrating the CGM. A possible origin of such shocks are mergers during the formation of such galaxies (Dolag et al. 2022). Their counterparts within galaxy clusters can be observed with current X-ray instruments, but detecting such features within galaxies at these distances is out of range for current instruments. New, ongoing ASKAP surveys are expected to deliver a large number of these sources, with the chance of finding also local ones. Indeed, recently archival ASKAP data revealed for the first time a candidate for such features in local galaxies at z~0.045 (CLOVERLEAF, Koribalski, in prep.). Given the size of these structures, their mean over-densitie of ~100 and their temperature slightly below 0.1 keV bring this in the range of opportunity (see Churazov, in prep) to detect the surface brightness jump associated to these shocks with the Line Emission Mapper (LEM) for such, close-by objects. In fact, depending on the metalicity, we predict order of few 100 counts for the post shock region in the very outskirts of such galaxies in a 100ks exposure, which will allow to test the formation mechanism of this newly detected class of objects. The distance of z~0.045 gives also a unique opportunity to distinguish the line emission within the CGM from elements like Oxygen (O VII and VIII) from the galactic foreground.

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