The atomic gas structure was found with the help of the Spherical Telescope with an aperture of five hundred meters. All galaxies are made up of their basic constituent, atomic gas. The main process of atomic gas accumulation and star formation from the intergalactic medium is how galaxies evolve.
Consequently, the study of theories of galaxy formation and evolution depends on the observation and study of atomic gas in and around galaxies. The simplest technique for probing atomic gas is to look at the 21 cm thin line emission of atomic hydrogen in the radio waveband.
What is 21 cm Hydrogen Emission?
Measurement of the 21 cm wavelength line of hydrogen gas allowed scientists to trace the distribution of hydrogen in our galaxy. Since visible light from stars cannot pass through dust clouds at 1420 MHz, this radiation from hydrogen can provide us with a more comprehensive view of hydrogen than is provided by stars.
The transition between the two levels of the 1s ground state of hydrogen is slightly separated by the interaction between electron spin and nuclear spin, generating 1420 MHz radiation. Hyperfine is a term for cleavage. The lower state of hydrogen will absorb 1420 MHz due to the quantum properties of the radiation, and the detection of 1420 MHz in emission indicates a previous excitation to the upper state.
Xu Cong, a researcher at the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), recently used the Five-hundred-metre Aperture Spherical Telescope (19-beam receiver) at 21 cm near the well-known compact galaxy group "Stephan's Quintet". performed deep mapping observations of the . These observations revealed a very large structure of atomic gas about 2 million light-years long.
The world's largest and most sensitive single dish radio telescope, FAST features the largest L-band multibeam feed array for 19 cm line observations with a 21-beam receiver. Full activation of the FAST 19 beam receiver opens a new window into atomic gas in the universe, especially for diffuse low-density gas far from galaxies.
According to XU, this is the largest structure of atomic gas ever discovered in a galaxy group. Observations are currently at this angular resolution, 1 per channelσ = 4.2 × 1016 cm−2 (Δv = 20 km h−1; angular resolution = 4′) are the most sensitive of the 21-cm line emission of atomic hydrogen.
Since its discovery in 1877 by the French astronomer Edouard Stephan, the Stephan Quintet has unraveled the mysteries of the complex web of connections between galaxies and between galaxies and the intragroup environment.
Recent studies reveal the presence of large-scale, diffuse, low-density gas far from the center of the group. This gas is most likely less than 1 gigayear old and18 cm−2 It has a column ID smaller than .
As it is unclear how low-density atomic gas can survive being ionized by the intergalactic UV background on such a long timescale, the data cast doubt on the current idea of galaxy-group formation/evolution.
Source: nature.com/articles/s41586-022-05206-x
Günceleme: 09/12/2022 17:56
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