Active black holes alter their galaxies' chemical distribution

Active supermassive black holes can considerably influence the presence and distribution of chemical molecules in their host galaxies.
Mrigakshi Dixit

The colossal black holes exert a complex and dynamic array of effects on their host galaxies, and astronomers continue to deepen their understanding of these phenomena.

According to a new study, active supermassive black holes can considerably influence the presence and distribution of chemical molecules in their host galaxies.

A team of scientists from the National Astronomical Observatory of Japan and Nagoya University evaluated the data collected by a robust network of telescopes: the Atacama Large Millimeter/Subsillimeter Array (ALMA) in Chile. 

Mapping the distribution of the molecules

Studying the surroundings of a black hole is a highly challenging task. 

Given the black holes’ tremendou distance from Earth, measuring the chemical composition distribution of the gas around it is even more difficult. 

Advanced facilities such as ALMA are required to see the galactic core, which is frequently obscured by thick stellar dust and gas. ALMA comprises 66 radio telescopes that work together to provide extraordinary observational capabilities.

In this study, ALMA focused on the central region of NGC 1068 (also known as M77), a barred spiral galaxy about 47 million light-years away in the direction of the constellation Cetus. 

The team combined the power of ALMA’s high spatial resolution and a new machine-learning analysis technique to map the distribution of molecules across two central regions of this galaxy. 

They discovered 23 different chemical molecule distributions in this galaxy. 

“This is the first survey to objectively depict the distribution of all detected molecules through unbiased observations,” noted the official release

The release further added: “The results show that along the path of the bipolar jets emanating near the black hole, molecules commonly found in galaxies such as carbon monoxide (CO) seem to break down, while the concentrations of distinctive molecules such as an isomer of HCN and the cyanide radical (CN) increase.”

Active black holes alter their galaxies' chemical distribution
Schematic diagram illustrating the location of the bipolar jet and galactic disk emanating from the supermassive black hole at the galaxy’s center, along with the resulting outflow of molecular gas

The supermassive black hole lurking at the center of this galaxy emits powerful polar jets that appear to impact the chemical composition.

This latest observation serves as compelling proof that supermassive black holes influence the overall structure and the chemical distribution of the galaxies they inhabit.

Moreover, this new study is vital to understanding the evolution of galaxies. 

The findings were reported in The Astrophysical Journal

Study abstract: 

We present an imaging molecular line survey in the 3 mm band (85–114 GHz) focused on one of the nearest galaxies with an active galactic nucleus (AGN), NGC 1068, based on observations taken with the Atacama Large Millimeter/submillimeter Array. 23 molecular transitions are obtained in the central ∼3 kpc region, including the circumnuclear disk (CND) and starburst ring (SBR) with 60 and 350 pc resolution. The column densities and relative abundances of all the detected molecules are estimated under the assumption of local thermodynamic equilibrium in the CND and SBR. Then, we discuss the physical and chemical effects of the AGN on molecular abundance corresponding to the observation scale. We found that H13CN, SiO, HCN, and H13CO+are abundant in the CND relative to the SBR. In contrast, 13CO is more abundant in the SBR. Based on the calculated column density ratios of N(HCN)/N(HCO+), N(HCN)/N(CN), and other molecular distributions, we conclude that the enhancement of HCN in the CND may be due to high-temperature environments resulting from strong shocks, which are traced by the SiO emission. Moreover, the abundance of CN in the CND is significantly lower than the expected value of the model calculations in the region affected by strong radiation. The expected strong X-ray irradiation from the AGN has a relatively lower impact on the molecular abundance in the CND than mechanical feedback.

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