Astronomers explore origin of optical variability in emission-line galaxies

New Chinese language analysis means that optical variability in emission-line galaxies (ELGs) is probably going attributable to star-formation exercise quite than the exercise of supermassive black holes.

The examine, carried out by astronomers from the Shanghai Astronomical Observatory (SHAO) of the Chinese language Academy of Sciences (CAS) together with scientists from the College of Science and Know-how of China, Yunnan Observatories, and the Polar Analysis Institute of China, was printed in The Astrophysical Journal on Nov. 17.

The scientists used a pattern of narrowband (NB) photographs of ELGs within the COSMOS discipline to check the galaxies’ optical variability. The 2-epoch photographs had been acquired 12~15 years aside.

ELGs are comparatively low-mass, effectively star-forming galaxies with much less dust. They’re typically thought to be plentiful within the early universe. Nebular traces, equivalent to Hα, can hint the star formation charge of galaxies, so ELGs are broadly used to check star formation and the evolution of galaxies throughout cosmic time in addition to reveal the star formation historical past of the universe.

On the identical time, systematic probes of the optical variability of such galaxies have been missing. Because of this, scientists have been unclear what proportion of ELGs present optical variability and what causes it.

To reply these questions, the researchers investigated the optical variability of a pattern of 181 ELGs. They used NB imaging knowledge obtained by the ground-based 8-meter Subaru telescope to verify NB photometric variation throughout the pattern.

After excluding the impact of the form of various NB filters, they discovered that lower than 3% of the pattern confirmed vital optical variability. The researchers then assessed the optically variable ELGs’ X-ray luminosity, mid-infrared exercise, radio exercise, morphology and different knowledge to find out the reason for the variability. Three origins of such variability are recognized: an active galactic nucleus (AGN), i.e., an energetic supermassive black hole; the explosion of a supernova throughout energetic star formation; or a stellar tidal disruption occasion.

Based on Lin Ruqiu, a Ph.D. pupil at SHAO and first creator of the examine, AGNs had been “not the primary contributors to the optical variability in these emission-line galaxies.”

Lin famous that high-resolution Hubble House Telescope photographs revealed the “merging morphology” of the ELGs, giving help to the concept supernovae are behind ELG optical variability.

“Star formation is enhanced in merging galaxies, and thus we might see extra energetic star formation actions equivalent to supernova explosions,” mentioned Lin.