Letter to the Editor

A Tale of NGC 3785: The formation of an ultra-diffuse galaxy at the end of the longest tidal tail

¹ Indian Institute of Astrophysics, II Block, Koramangala, Bengaluru 560 034, India
² Pondicherry University, R.V. Nagar, Kalapet, 605014 Puducherry, India
³ SKA Observatory, Jodrell Bank, Lower Withington, Macclesfield, SK11 9FT, UK
⁴ National Centre for Radio Astrophysics, TIFR, Post Bag 3, Ganeshkhind, Pune 411 007, India

^⋆ Corresponding author; chandan@iiap.res.in

Received: 27 August 2024
Accepted: 16 October 2024

Abstract

Aims. We present the discovery of an extended and faint tail observed in the isolated environment associated with galaxy NGC 3785. This study additionally provides observational evidence supporting the formation of ultra-diffuse galaxies (UDGs) at the end of the tail.

Methods. We utilized the Gnuastro software to detect and analyze the low surface brightness structures in the optical g- and r-bands using data from the Dark Energy Camera Legacy Survey. We created a detection map to identify the faint tail and measured its length using cubic spline fitting. Additionally, we found 84 star-forming clumps along the tail and performed photometric analysis on the tail portion after applying a significance threshold on the signal-to-noise ratio.

Results. We have measured the projected length of the tail, which is ∼390 kpc. We propose that this tail arises from the interaction of the NGC 3785 with a gas-rich galaxy, which ends up as a UDG at the end of the tail.