UV imaging tracks birth of stars outside galaxies in hi-res detail

With UVIT, star-forming features outside galaxies are better resolved which is critical in studying ongoing star formations at small scales

In a new study that could enable closer, deeper probes into the formation of stars outside the galaxies due to galactic interactions, an international team of astronomers has presented high-resolution ultraviolet imaging observations of an interacting galaxy system.

The team comprising astronomers from India, Australia, Canada, Germany, and France made the observations on star-forming regions around the interacting galaxy system NGC 5291, using data from the Ultraviolet Imaging Telescope (UVIT) on board AstroSat, Isro’s multi-wavelength space astronomy observatory.

Members of the team – Rakhi R, Koshy George, and Smitha Subramanian – told DH that the project was aimed at studying knots (gas and dust clumps where stars are formed) and the rate at which stars are being formed in these knots, at the best possible resolution. The paper has been accepted for publication in the June issue of the Monthly Notices of the Royal Astronomical Society.

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NGC 5291 is an interacting galaxy system in the western outskirts of the cluster Abell 3574 and comprises a companion galaxy, The Seashell. Rakhi, an Assistant Professor of Physics at the NSS College in Pandalam, Kerala, led the study. She said the team investigated the rate of star formation in the main system and within the ring of neutral hydrogen (HI) formed after the collision of NGC 5291 with The Seashell.

The study on the ongoing star formation in Tidal Dwarf Galaxies (TDGs) in the interacting system led to the identification of 57 star-forming knots including 12 new detections. TDGs take shape in the tidal arms of debris from the collisions or mergers of galaxies. Hierarchical clustering involves the merging of dwarfs to form big galaxies while these TDGs are newer galaxies that are formed from gas thrown out of big galaxies after they collide or merge.

Koshy George is a researcher at the Faculty of Physics, Ludwig Maximilian University, Munich, and Smitha Subramanian is an Assistant Professor in Extragalactic Astronomy at the Indian Institute of Astrophysics (IIA), Bengaluru.

In higher resolution

The team used UV imaging in the study because young, recently formed stars emit large amounts of UV radiation, making the star formation appear significantly brighter in these images. The results presented in this study improve on previous observations of the system that were made through GALEX (Galaxy Evolution Explorer, NASA’s orbiting space telescope). With UVIT, the star-forming features outside the galaxies are better resolved which is critical in studying the ongoing star formations at small scales.

UVIT is a unique instrument with a wide field of view and an angular resolution of 1.2 arcseconds. An arcsecond is an angular measurement equalling 1/3600 of a degree. AstroSat was launched in September 2015. UVIT, developed by IIA, is one of its five payloads with two telescopes covering the Far UV and Near UV bands.

PhD and MSc students were also involved in the project which commenced in July 2022. The team said the study was also about training the next generation of astronomers using a world-class facility with data at the finest resolution.