Three-dimensional distribution of molecular & atomic hydrogen in galaxies

Published: 31st May, 2021

A researcher has estimated the three-dimensional distribution of molecular and atomic hydrogen in a nearby galaxy which can help lead to clues to the star formation processes and the evolution of the galaxy.

Context

The research was conducted at Raman Research Institute (RRI), Bengaluru, an autonomous organisation of the Department of Science and Technology (DST), Government of India.
It was funded by the DST, Government of India.

Key Features of the Study

The estimates are based on the phenomenon of the galaxies like, the Milky Way, which consists of discs containing stars, molecular and atomic hydrogen, and helium.
The estimation was carried out by mathematical calculations on the computer and used publicly available data.
Study: Under the study a single galaxy about 20 million light-years away from the Milky Way was focused.
- The spectral lines of carbon monoxide (CO) were studied to accurately trace molecular hydrogen, whose spectral lines are more difficult to observe.

What are Spectral lines?

These are narrow emission or absorption features in the spectra of gaseous and ionized sources.
Spectral lines are powerful diagnostics of physical and chemical conditions in astronomical objects.
Their rest frequencies identify the specific atoms and molecules involved, and their Doppler shifts measure radial velocities.
- These velocities yield the redshifts and Hubble distances of extragalactic sources, plus rotation curves and radial mass distributions for resolved galaxies.

- Spectral lines of the CO molecule are used to infer the three-dimensional distribution of both the narrow disc component and the diffuse component of molecular hydrogen.

What is the role of Molecular Hydrogen gas in star formation?

The molecular hydrogen gas converts to individual stars under the pull of gravity, thus holding clues to the star formation processes and the evolution of the galaxy.
- The atomic hydrogen extends both above and below the discs.
- It has also been estimated that molecular hydrogen extends farther from the disc in both directions, up to about 3000 light-years.
- This gaseous component is warmer than the one straddling the disc and has comparatively lesser densities. This is known as the ‘diffuse’ component of the molecular disc.

What are the outcomes of the study?

The research says that the extension of gas may explain the occurrence of stars at a few thousand light-years perpendicular to the galactic disc.
- Research found that the diffuse component makes up about 70 percent of the molecular hydrogen, and this fraction remains roughly constant along the radius of the disc.

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Three-dimensional distribution of molecular & atomic hydrogen in galaxies

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