Chinese scientists conducted a study and found that the optical variability of galaxies with emission
Scientists used a sample of narrowband (NB) ELG images to study the optical variability of galaxies. Images of two eras of their development were obtained with a difference of 12–15 years.
ELGs are relatively low-mass galaxies.with efficient star formation and less dust. It is believed that there were many of them in the early Universe. They are used to study star formation and the evolution of galaxies.
However, no one has systematicallystudies of the optical variability of such objects. As a result, scientists could not understand what percentage of ELG exhibits optical variability and what causes it.
To answer these questions, astronomers examined the optical variability of a sample of 181 ELGs. They used NB image data obtained using the ground-based Subaru 8-meter telescope.
Image clippings of five ELG optical variables.
From left to right are images of the SC-NB816, SC-i’, HSC-NB816, HSC-i and HSC/ACS-i channels, respectively. Source: SHAO
In the study, scientists excluded the influenceshapes of different NB filters and found that less than 3% of galaxies exhibit significant optical variability. The researchers then assessed the X-ray brightness of the ELG optical variables, activity in the mid-infrared and radio wavelengths; morphology and other data to determine the cause of variability. Three sources of such variability are known: an active galactic nucleus (AGN), i.e. an active supermassive black hole; supernova explosion during active star formation; or a stellar tidal disruption event.
According to scientists, AGNs “did not make a major contribution” to the optical variability of galaxies with emission lines. It's all about supernovae and active star formation.
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