About 430 million light years from Earth, in the Leo constellation, a new ultra-diffuse galaxy has been discovered to be under formation at the end of the tidal tail, a long, thin stream of stars and interstellar gas, of galaxy NGC 3785. The discovery of the galaxy formation, driven probably by the gravitational interaction between NGC 3785 and a neighbouring galaxy. marks a major milestone in understanding galaxy evolution.

NGC 3785 galaxy is known to possess the longest tidal tail discovered so far. The tail extends from the galaxy and is formed due to gravitational forces ("tidal forces") when two galaxies interact closely, essentially pulling material away from each other during a close encounter or merger process.

When astronomers from the Indian Institute of Astrophysics (IIA), an autonomous institution of Department of Science and Technology and their collaborators looked carefully at the galaxy NGC 3785, they found that not only does it have the longest tidal tail discovered so far, but that an ultra-diffuse galaxy is currently being formed at the end of this tidal tail as well.

A seemingly longer than average tidal tail consisting of a stream of stars and gas, was chanced upon by Omkar Bait a few years ago, when he was a student at the National Centre for Radio Astrophysics (NCRA) in Pune. Recognising that this was a unique object, this discovery was shared with Yogesh Wadadekar (NCRA) and Sudhanshu Barway at IIA. They worked together on the subsequent study. 

“We decided to look at this extraordinary galaxy and its giant tidal tail in great detail”, said Chandan Watts, a Ph.D. student at IIA and the first author of the paper that has since been published. He carried out a careful photometric analysis of the tail and measured its extent and length accurately using advanced image processing techniques. “We found that this extraordinary tidal tail stretches for 1.27 million light years, making this the longest tidal tail discovered so far,” he added.

The tail is not only remarkable in its size, it also offers clues to the formation of ultra-diffuse galaxies (UDGs). The unique aspect of this tail is that a nascent ultra-diffuse galaxy has formed at its tip, likely driven by the gravitational interaction between NGC 3785 and a neighbouring galaxy—making it a rare and exciting discovery.

“This particular tail's extraordinary length and the presence of star-forming clumps along its span make it a unique case for understanding how faint and diffuse galaxies come into existence”, said Sudhanshu Barway, a faculty member at IIA and co-author of the study.

“This discovery highlights the fascinating process of galaxy interaction and how it can create new, faint, and diffuse structures,” explains Chandan. "The tidal tail offers a glimpse into how galaxies like ultra-diffuse ones, with very low surface brightness, come into being."

The new discovery promises to advance our understanding of low surface brightness features, which are often missed by traditional surveys due to their faintness. Recently launched missions like the Euclid Space Telescope and upcoming ground-based surveys such as the Rubin Observatory's Legacy Survey of Space and Time (LSST) will be instrumental in uncovering more such faint tidal features thanks to their enhanced sensitivity.

The research has been published in the November issue of the European journal, Astronomy & Astrophysics Letters. It is authored by Chandan Watts, from IIA and Pondicherry University, Dr. Sudhanshu Barway from IIA, Dr. Omkar Bait from SKA, U.K., and Dr. Yogesh Wadadekar from National Centre for Radio Astrophysics, Pune.

The enhanced tail features of NGC 3785 are shown in a reversed grey scale image. The regions of high brightness are shown in color to highlight the different features. The longest known tidal tail can be seen extending towards the bottom right from NGC 3785, culminating in the Ultra Diffuse Galaxy (UDG) in formation.

***

NKR/PSM

(Release ID: 2090582) Visitor Counter : 1376