Scientists discover the farthest Gamma-ray emitting active galaxy

Vijay Mohan
Tribune News Service
Chandigarh, April 13

Astronomers have discovered a new active galaxy, identified as the farthest gamma-ray emitting galaxy, that has so far been stumbled upon. This active galaxy called the Narrow-Line Seyfert 1 (NLS1) galaxy, which is about 31 billion light-years away, opens up avenues to explore more such gamma-ray emitting galaxies.

Ever since 1929, when Edwin Hubble discovered that the Universe is expanding, it has been known that most other galaxies are moving away from us.

Light from these galaxies is shifted to longer wavelengths.

As wavelength gets longer, the hue of light turns redder which is termed as ‘redshifted'. Scientists have been trying to trace such red-shifted galaxies to understand the early Universe.

Scientists from Aryabhatta Research Institute of Observational Sciences (ARIES), Nanital, in collaboration with researchers from other institutions, studied around 25,000 luminous Active Galactic Nuclei (AGN) and found a unique object that emits high-energy gamma rays located at a high red-shift.

They identified it as a gamma-ray emitting NLS1 galaxy, which is a rare entity in space.

The Sloan Digital Sky Survey (SDSS), a major optical imaging and spectroscopic survey of astronomical objects that have been in operation for the last 20 years was used for the study.

Powerful relativistic jets, or sources of particles in the Universe travelling nearly at the speed of light, are usually produced by AGN powered by large black holes and hosted in a giant elliptical galaxy.

However, the detection of gamma-ray emission from NLS1 challenges the idea of how relativistic jets are formed because NLS1s are a unique class of AGN that are powered by the black hole of low mass and hosted in a spiral galaxy.

As of today, gamma-ray emission has been detected in about a dozen NLS1 galaxies, which are a separate class of AGN identified four decades ago. All of them are at lower redshifts, and no method was available to date to find NLS1 at higher redshifts.

This opens up a new way to find gamma-ray emitting NLS1 galaxies in the early Universe.

For the research, the scientists used one of the largest ground-based telescopes in the world, the 8.2 m Subaru Telescope located in Hawaii, USA.

They helped establish a new method to find high red-shift NLS1 galaxies that were not known previously by comparing different emission lines in their spectra.

The new gamma-ray emitting NLS1 was formed when the Universe was only about 4.7 billion years old as compared to its current age of about 13.8 billion years.

The research was led by Dr Suvendu Rakshit from ARIES, Other in the team included CS Stalin, Vaidehi S Paliya and Indrani Pal from India, Malte Schramm from Japan, I Tanaka from the USA, Jari Kotilainen from Finland and Jaejin Shin from South Korea.