The study investigates the double nuclei in the remnant of the merger of the Mrk 212 galaxy


The study investigates the double nuclei in the remnant of the merger of the Mrk 212 galaxy

The SDSS color composite image of Mrk 212. The slit position of the HCT observations is indicated by the dashed line. Mrk 212 is referred to as Source 1 (S1) and the companion as Source 2 (S2). Credit: Rubinur et al., 2020.

Using the Karl G. Jansky Very Large Array (VLA) and the updated Giant Meter Radio Telescope (uGMRT), astronomers conducted multi-wavelength observations of a remnant of galaxy fusion known as Mrk 212. Results of this campaign of observation, presented in a paper published on October 28 on, sheds more light on the properties and nature of this residue.

Galactic mergers play an essential role in the evolution of galaxies. Large mergers even have the ability to change the shape of parent galaxies and form an object with a completely new morphology.

Observations show that the influx of gas during galactic mergers can trigger mass accretion on supermassive black holes (SMBHs), turning them into active galactic nuclei (AGN). When both SMBHs are turned on at the same time, they can form AGN pairs. If the separation between the two AGNs is less than 326 light years, they are known as binary AGNs. In case the separation is greater, astronomers call them dual AGN.

At a distance of brightness of about 322 million light years, Mrk 212 is a remnant of galaxy fusion with two known radio sources associated with two optical nuclei, designated S1 and S2. The predicted separation between the two nuclei is estimated to be around 18,250 light years, making it a double AGN candidate.

A team of astronomers led by Khatun Rubinur of the Indian Institute of Astrophysics in Bangalore, India, made deep, optical and ultraviolet radio observations of Mrk 212 using VLA and uGMRT. The main objective of this monitoring campaign was to confirm the AGN dual nature of the object and provide more information on the properties of this source.

“We conducted a multi-wavelength study of the merging galaxy Mrk 212, which possesses two optical nuclei S1 and S2 with an expected separation of ∼ 11.8 ” or ∼ 6 kpc,” the astronomers wrote in document.

VLA observations revealed a double radio source associated with S1 and a compact radio structure associated with S2. The VLA images also show an extended 8.5 GHz radio structure which, located one arc second away from the S2 optical cores, which has a relatively flat spectral index and is assumed to be a compact core.

The researchers found that S1’s total span is about 2,445 light years and its average spectral index of 1.4-8.5 GHz is at a level of about -0.81. These properties indicate that S1 looks like a compact symmetrical object (CSO).

According to the study, the presence of the compact radio nucleus and the presence of AGN emission lines in the S2 optical spectrum suggest the presence of another AGN in S2. Furthermore, optical observations show that S1 and S2 both fall in the AGN + SF (star formation) region in the BPT diagram (Baldwin, Philips and Terlevich). All in all, the astronomers concluded that the results obtained strongly support the double AGN nature of Mrk 212.

New residual radio galaxy detected

More information:
Rubinur et al., A Multi-wavelength Study of the Dual Nuclei in Mrk 212, arXiv: 2010.14914 [astro-ph.GA]

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