Radio Relics in Merging Galaxy Cluster PSZ2 G200.95-28.16

In the vast universe, there are groups of galaxies bound together by gravity, known as Galaxy Clusters. Sometimes, these clusters collide and merge. When they do, they create something quite spectacular: Radio Relics. These are giant, glowing arcs of radio waves that appear on the outskirts of these merging clusters. Think of them as cosmic graffiti left behind by the energetic events of a galaxy cluster’s tumultuous history.

Today, we will look at one such merging cluster called PSZ2 G200.95-28.16. This cluster is a bit on the smaller side compared to its neighbors, but it boasts three interesting radio relics. Our research team has employed advanced radio telescopes to gather new data, paired with X-ray observations, to understand what’s going on with this cosmic dance.

#What Are Radio Relics?

Imagine the aftermath of a car crash. The sound of crumpling metal and glass scattering everywhere is akin to the shock waves produced during a merger of galaxy clusters. When these clusters collide, they generate shocks that accelerate cosmic rays-tiny particles traveling close to the speed of light. As these energized particles interact with magnetic fields found in the cluster, they emit radio waves, creating radio relics.

Radio relics have a distinct arc-like shape and are often polarized, which means their light has a preferred direction of oscillation. They are important clues that help scientists understand the energetic processes at play during galaxy cluster mergers.

#The Cluster PSZ2 G200.95-28.16

PSZ2 G200.95-28.16 is an intriguing low-mass galaxy cluster located in the cosmos. It was first spotted by the Planck Satellite and later confirmed using X-ray data. This cluster is particularly exciting because it contains not one, not two, but three radio relics-each presenting a unique cosmic story.

We have named the most prominent relic “Seahorse” due to its distinctive shape. The other two relics will be referred to as R2 and R3.

#New Observations

To learn more about PSZ2 G200.95-28.16, we utilized advanced radio telescopes: the Upgraded Giant Metrewave Radio Telescope (uGMRT) and the MeerKAT telescope. We took observations at various frequencies-400 MHz, 650 MHz, and 1283 MHz. In addition, we used data from the Chandra X-ray Observatory to add depth to our research.

In our images, we found the largest sizes of the three relics to be 1.53 Mpc for Seahorse, 1.12 kpc for R2, and 340 kpc for R3. Polarization measurements revealed that all three relics are polarized at 1283 MHz, providing more insights into their structure.

#The Unique Features of the Radio Relics

#Seahorse

The Seahorse is the star of the show, standing out for its unique morphology. It features a bent head, a body with a notch, and an elongated tail. The brightness of this relic suggests it is the result of intense energetic processes, possibly linked to shocks from the merging cluster.

Interestingly, the Seahorse has shown signs of spectral steepening towards the cluster center, which hints at the direction of the merger shocks. We estimated the Mach number, a measure of shock strength, to be around 2.5.

#R2

R2 is more complicated. It sports two structures: a bright diffuse area and a fainter filament. When we examined R2 closely, we noted variations in its brightness between different frequency bands, indicating that its true nature is more complex than it first appears.

The estimated Mach number for R2 is about 3.5, indicating that it is also influenced by strong shocks.

#R3

Finally, we have R3, which is the smallest of the three relics. It resembles an inverted arc and rests in the cluster’s northwest region.

While R3 is not as bright as Seahorse or R2, it still provides valuable insight into the cluster’s dynamics.

#Polarization Measurements

One of the intriguing features of these radio relics is their polarization. Our analysis showed that all three relics exhibit linear polarization, which is good news for understanding their magnetic fields.

The Seahorse had an average polarization of around 15%, with the electric field vectors aligning along the relic’s structure. R2 displayed a similar alignment, while R3 had a less clear magnetic field distribution due to its faint nature.

#The Role of X-rays

In addition to our radio observations, we employed X-ray data to gather a comprehensive view of the merging cluster. The X-ray surface brightness map revealed two prominent Subclusters, which are regions of intense heat and activity.

However, in a twist, we noticed that the radio relics weren’t aligned perpendicularly to the expected merger axis, something we usually see in other clusters. In fact, we did not detect any shocks in the locations where the relics are found. This contradiction raises questions about the merging history of PSZ2 G200.95-28.16.

#Possible Scenarios and Theories

With all this information in hand, we began to explore possible scenarios that could explain the observations. One theory suggests that the merger produced both axial and equatorial shocks. Axial shocks arise from the merging direction, while equatorial shocks expand outward.

Given the unusual positions of the radio relics, we also considered the possibility that PSZ2 G200.95-28.16 is experiencing an off-axis merger, where the clusters collide at an angle. This could explain the varying shock strengths and the resultant radio relic structures.

Another option is that multiple merging events are occurring simultaneously. If so, different axes of merging could contribute to the observed radio relics, but further investigation will be needed to confirm this.

#The Odd Radio Ring

While investigating the cluster, we stumbled upon a peculiar radio ring in our uGMRT images. This ring is about 100 kpc in size and has sparked curiosity among scientists.

It resembles what are known as Odd Radio Circles (ORCs)-mysterious, round radio sources that have been discovered in recent times. While we can’t say for certain if this is indeed an ORC, its formation likely involves interactions with the intracluster medium during the merger process, stirring up radio emissions.

#Conclusions

PSZ2 G200.95-28.16 is a thrilling low-mass galaxy cluster featuring three captivating radio relics. Through our observations, we managed to capture the unique characteristics of Seahorse, R2, and R3 while posing questions about the cluster's merger dynamics.

The merging process in this cluster is complex, leading to various radio emissions that challenge our existing theories. Our work emphasizes the importance of continuing to study these cosmic events, as they provide essential insights into the universe's evolution.

In the end, this study showcases the fascinating interactions happening in the cosmos and how radio relics serve as windows into these spectacular events. Who knew the universe could have such a flair for drama?