- The paper presents the discovery of ORC J0102–2450, a circular extragalactic radio source detected at 944 MHz with ASKAP.
- It details a 70‑arcsecond ring morphology and explores formation scenarios including giant radio lobes, blast waves, and galaxy interactions.
- The findings underscore the need for deeper multiwavelength surveys to understand galaxy formation dynamics and supermassive black hole activity.
The paper presents the discovery of a novel extragalactic radio source, Odd Radio Circle (ORC) J0102--2450, utilizing observations from the Australian Square Kilometre Array Pathfinder (ASKAP) at 944 MHz. This finding adds to a growing class of mysterious radio structures known as Odd Radio Circles (ORCs), which have been detected solely in radio wavelengths with no counterparts in optical or infrared spectra.
Observational Findings
ORC J0102--2450 exhibits a circular symmetry with a diameter of approximately 70 arcseconds, correlating to about 300 kpc if aligned with the central elliptical galaxy DES J010224.33--245039.5 at a redshift of z∼0.27. This ORC is characterized by a pronounced radio ring surrounding a central core, yet lacks corresponding emissions in non-radio wavelengths.
ASKAP’s rigorous data processing, combined with multi-epoch observations, allowed the detection of this faint radio ring amidst a complex background. The potential interaction of ORC J0102--2450 with neighboring galaxies, particularly with DES J010226.15--245104.9, situated within the ring's southeastern segment, warrants further investigation into interaction scenarios.
The paper explores several hypotheses regarding ORC formation:
- Giant Radio Lobes Viewed End-On: One theory posits that ORCs could be relic lobes of giant radio galaxies viewed end-on. Such a perspective could align with the symmetrical morphology and the presence of underlying elliptical hosts, with ORC J0102--2450 suggested as a possible manifestation of this scenario.
- Remnants of a Giant Blast Wave: Another conceptual framework considers the ORC as the remnant of a colossal blast wave, perhaps resulting from events such as binary supermassive black hole mergers or other powerful transient astrophysical occurrences. The symmetric blast wave could facilitate the formation of a spherical shock front, observed as a radio ring.
- Galactic and Intergalactic Medium Interactions: The interactions between galaxies, or with the surrounding intergalactic medium, might also account for the observed circular structures. Particular configurations of bent jets or radio tails from galaxies could manifest as ORCs.
Implications and Future Directions
The detection of ORC J0102--2450 bolsters the hypothesis that certain unknown physical mechanisms lead to the creation of these large, ring-like radio structures. Further ORC discoveries will be crucial in validating these scenarios. The identification and analysis of additional ORCs are expected to benefit from upcoming surveys with increased sensitivity and resolution, such as those conducted by LOFAR or MeerKAT.
From a theoretical perspective, understanding ORCs could significantly enhance our comprehension of the dynamics involved in galaxy formation and evolution, as well as the active phases of supermassive black holes.
As the exploration of ORCs progresses, integrating multi-wavelength studies, alongside advances in theoretical modeling of radio galaxies and cosmic structures, will be indispensable in unraveling the nature and origins of these enigmantic radio phenomena.