MATHEMATICAL SCIENCES

An international team of researchers has discovered special galaxies in the Green Pea Galaxy


Recently, an international research team used samples found by the Guo Shoujing Telescope (LAMOST) to find 5 special galaxies with bimodal narrow lines in nearly 1550 green pea galaxies, and analyzed that such special objects may originate from the merger of active galactic nuclei. The findings were published July 19 in the Monthly Notices of the Royal Astronomical Society.

Green Pea Star Image source: NASA

According to reports, the Green Pea Galaxy is named for its green and dense optical form, with extremely strong emission lines, especially ionized oxygen emission lines. Green Pea galaxies are usually low-redshift galaxies with small masses , metal-poor abundance , and active star formation activity , and are thought to be their counterparts in the neighboring universe of earlier galaxies. Some green pea galaxies show signs of activity in active galactic nuclei, characterizing the activity of supermassive black holes in the nuclear region.

Therefore, the systematic search and study of the Green Pea Galaxy can help astronomers better understand the formation and evolution of early galaxies, and study the active galactic nucleus (AGN) samples of the Green Pea Galaxy to bring enlightenment to the study of the co-evolution of early supermassive black holes and host galaxies.

The early universe and high redshift galaxy cluster group led by Zheng Zhenya, the corresponding author of the paper and a researcher at the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, and researchers from many research units at home and abroad, such as the University of Chinese Academy of Sciences, the University of Science and Technology of China, NASA’s Goddard Space Flight Center, and the University of Manitoba in Canada, carried out joint research to analyze the spectral emission line profile based on the green pea galaxy samples of LAMOST’s extragalactic sky survey project.

Studies have shown that the green pea galaxy sample from the LAMOST extragalactic survey project is the largest pea galaxy spectral search sample, including nearly 1550 pea galaxy spectra, more than double the number of pea galaxy samples verified by the previous Sloan Digital Sky Survey (SDSS) project.

Based on X-ray, mid-infrared, radio and other multi-band photometric and spectroscopic data, the researchers used energy spectrum fitting and optical line diagnosis to verify AGN activity in this sample with high confidence. Combining the emission line profile as well as the optical morphology, the researchers believe that the physical source of the bimodal profile of these galaxies is more likely to be the merger of binically active galactic nuclei, rather than outflow or gas disks.

Lin Ruqiu, the first author of the paper and a doctoral student at the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, said that the composition of the bimodal emission line of the five green pea galaxies is very narrow, the morphology is dense and cannot distinguish the disk structure and there is no obvious tilt angle, so the possibility of the twin peaks originating from the outflow or gas disk is low.

Zheng Zhenya said that these 5 green pea galaxies have a stronger contour width (the ratio of line strength to continuous spectrum) than the bimodal emission line galaxies in the general type II active galaxy nucleus, and the cause of this phenomenon may be related to the merger of galaxies in the early universe. “Next, the Green Pea Galaxy survey project in the third phase of the LAMOST spectral survey program is expected to provide us with more samples of such special galaxies, thereby further revealing the co-evolution of massive galaxies and supermassive black holes.” (Source: Shen Chunlei, China Science News)

Related paper information:https://doi.org/10.1093/mnras/stad1857



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