Large radio bubble detected in the galaxy NGC 4217

An international team of astronomers has carried out radio observations of a star-forming galaxy known as NGC 4217. The observation campaign detected a large radio bubble in the galaxy’s halo. The discovery was reported in a paper published September 23 on the preprint server. arXiv.

Located approximately 61.6 million light years away, NGC 4217 is a nearby star-forming spiral galaxy. Previous observations of this galaxy have shown that it contains dozens of absorbing dust structures of various morphologies. Additionally, a radio halo extending out to about 16,000 light-years from the galaxy’s star-forming disk has been identified.

Recently, a group of astronomers led by Volker Heesen of the University of Hamburg in Germany used the Jansky Very Large Array (JVLA) and the LOw Frequency ARray (LOFAR), to take a closer look at NGC 4217 in the radio band.

“We present new observations of the galaxy NGC 4217 CHANG-ES (Continuum HAloes in Near Galaxies—an EVLA Survey) in S-band (2-4 GHz), which we combine with the LoTSS-DR2 archive (LOFAR Two-meter data Sky Survey) version 2) data at 144 MHz,” the researchers wrote in the paper.

The observations detected a visible extension of the radio continuum emission in the northwest halo of NGC 4217. Closer inspection of this emission allowed Heesen’s team to identify a very extended faint component that had previously escaped detection.

The images show that this component has the morphology of a bright-edged bubble extending to a distance of 65,000 light-years from the star-forming disk.

According to the paper, the emission is amplified along the walls of NGC 4217’s radio bubble with a slight depression in the center of the bubble. The northeast edge of the bubble is particularly prominent and the images collected suggest the potential presence of a shell on this side.

The study found that the scale heights of the radio bubble are 19,200 and 9,400 light years, respectively, at 144 MHz and 3 GHz. Therefore, they are several times larger than the typical heights of radio bubbles in edge galaxies. The total magnetic field intensity of the bubble in NGC 4217 was measured to be around 11 µG.

Additionally, astronomers estimated that at the edge of the bubble, wind speed increases by about 300 to 600 km/s, or approximately the level of the escape velocity of NGC 4217.

This result suggests that the bubble can be inflated by about 10% of the kinetic energy injected by supernovae on its dynamic time scale of 35,000 years. However, the researchers note that not all of the kinetic energy can be used to inflate the bubble, because large fractions can be radiated.

© 2024 Science X Network