A map of the atomic hydrogen (HI) 21-cm line emission (revealed as the red haze) in the vicinity of Stephans Quintet, a famous compact group of galaxies discovered in 1887, overlaid on a deep optical color image. Credit: NASA, ESA, CSA, and STScI
The atomic gas structure was found utilizing the Five-hundred-meter Aperture Spherical Telescope..
Atomic gas is the essential product from which all galaxies are formed. The evolution of galaxies is mostly a process of accreting atomic gas from the intergalactic medium and transforming it into stars.
As a result, the observation and research study of atomic gas in and around galaxies are important to the research study of galaxy development and evolution designs. Observing the 21-cm fine structure line emission of atomic hydrogen in the radio waveband is the most direct way to explore atomic gas.
Recent deep mapping observations of 21-cm line emission in the area of the widely known compact group of galaxies “Stephans Quintet,” utilizing the Five-hundred-meter Aperture Spherical Telescopes (19-beam receiver) led by Xu Cong, a scientist from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), exposed a very big atomic gas structure with a length of about 2 million light-years (about 20 times the size of the Milky Way).
The discovery was recently published in the journal Nature..
FAST is presently the biggest and most delicate single-dish radio telescope in the world, and its 19-beam receiver is the biggest L-band multi-beam feed array for 21-cm line observations. The full commissioning of the FAST 19-beam receiver opened a new window on atomic gas in the Universe, particularly for low-density diffuse gas far from galaxies.
” This is the biggest atomic gas structure ever found around a galaxy group,” said XU. The observations reached a sensitivity of 1σ= 4.2 × 1016 cm-2 per channel (Δv= 20 km s-1; angular-resolution= 4 ′), making them presently the most sensitive observations of atomic hydrogen 21-cm line emission at this angular resolution.
Ever given that its discovery by the French astronomer Edouard Stephan in 1877, Stephans Quintet has continued exposing puzzles associated with the complex web of galaxy-galaxy and galaxy-intragroup medium interactions in the group.
The new observations reveal that massive, diffuse, low-density gas (with a column identity less than 1018cm-2) exists far away from the center of the group, and it is most likely that the gas has actually been there for ~ 1 giga years. The observations challenge the present theory of galaxy-group formation/evolution since it is unclear how the low-density atomic gas can make it through ionization by the intergalactic UV background on such a long time scale.
Referral: “A 0.6 Mpc H i structure associated with Stephans Quintet” by C. K. Xu, C. Cheng, P. N. Appleton, P.-A. Huang, U. Lisenfeld, and F. Renaud, 19 October 2022, Nature.DOI: 10.1038/ s41586-022-05206-x.
Reference: “A 0.6 Mpc H i structure associated with Stephans Quintet” by C. K. Xu, C. Cheng, P. N. Appleton, P.-A. Tang, M. Yun, Y. S. Dai, J.-S. Huang, U. Lisenfeld, and F. Renaud, 19 October 2022, Nature.DOI: 10.1038/ s41586-022-05206-x.
