The sharpest ultraviolet view of the star formation in an extreme environment of the nearest Jellyfish Galaxy IC 3418

Abstract

We present the far ultraviolet (FUV) imaging of the nearest Jellyfish or Fireball galaxy IC3418/ VCC 1217, in the Virgo cluster of galaxies, using Ultraviolet Imaging Telescope (UVIT) onboard the AstroSat satellite. The young star formation observed here in the 17 kpc long turbulent wake of IC3418, due to ram pressure stripping of cold gas surrounded by hot intra-cluster medium, is a unique laboratory that is unavailable in the Milky Way. We have tried to resolve star forming clumps, seen compact to GALEX UV images, using better resolution available with the UVIT and incorporated UV-optical images from Hubble Space Telescope archive. For the first time, we resolve the compact star forming clumps (fireballs) into sub-clumps and subsequently into a possibly dozen isolated stars. We speculate that many of them could be blue supergiant stars which are cousins of SDSS J122952.66?112227.8, the farthest star (*17 Mpc) we had found earlier surrounding one of these compact clumps. We found evidence of star formation rate (4-7.4 9 10 -4 M yr -1 ) in these fireballs, estimated from UVIT flux densities, to be increasing with the distance from the parent galaxy. We propose a new dynamical model in which the stripped gas may be developing vortex street where the vortices grow to compact star forming clumps due to self-gravity. Gravity winning over turbulent force with time or length along the trail can explain the puzzling trend of higher star formation rate and bluer/younger stars observed in fireballs farther away from the parent galaxy.

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE)

“…The VESTIGE survey has also detected several HII regions located well outside the star-forming discs of Virgo cluster galaxies formed within the gas stripped during the interaction with the surrounding environment. Typical examples of these extraplanar star-forming regions are those detected in the tail of IC3418 that probably formed after a ram-pressure-stripping event (VCC1217; Hester et al 2010, Fumagalli et al 2011b, Hota et al 2021, those located in between UGC 7636 and M49 that formed by a combined effect of ram-pressure stripping within the halo of M49 and gravitational interactions between the two galaxies (VCC 1249; Arrigoni- Battaia et al 2012), or those located along the long HI tail of NGC 4254 that formed after a gravitational perturbation in a high-speed fly-by encounter with another cluster member (Vollmer et al 2005, Duc & Bournaud 2008, Boselli et al 2018b. It has been claimed that these regions, characterised by stellar masses of 10 3 M star 10 5 M and star formation rates of 10 −5 S FR 10 −3 M yr −1 , might become gravitationally unbound systems and thus be at the origin of compact objects such as globular clusters or ultracompact dwarf galaxies (UCDs) typical of rich environments.…”

ViCTORIA project: MeerKAT H I observations of the ram pressure stripped galaxy NGC 4523

“…The green numbers are the ages in Myr for E(B − V) = 0.1. Jáchym et al 2013;Kenney et al 2014;Hota et al 2021), at least at the sensitivity of the available observations. The process of star formation and the conditions under which this occurs in the tails of stripped material is still poorly known.…”

Dorado and its member galaxies

“…therein). More recently, high spatial resolution FUV studies using Astrosat-UVIT investigated ram-pressure stripping in action in cluster jelly-fish galaxies (George et al 2018;Hota et al 2021).…”