Star Formation in Young Stellar Clumps of Ram-Pressure Stripped Galaxies as seen by HST
Eric Giunchi (DIFA - Alma Mater Studiorum Univ. di Bologna)
Tuesday 16/04/2024 @ 14:00, Sala Antonio Sollima (IV piano Battiferro)
Young stellar clumps are found embedded in the gaseous tails of galaxies undergoing intense ram-pressure stripping (RPS) in galaxy clusters, so-called jellyfish galaxies. These clumps offer a unique opportunity to study star formation under extreme conditions, in the absence of an underlying disk and embedded within the hot intracluster medium (ICM). We present the first statistically robust sample of star-forming clumps and complexes of six jellyfish galaxies from the GASP survey, detected independently in H?, UV and V-band with UVIS/WFC3, at a spatial resolution of about 140 pc. The sample includes 2406 H? clumps and 3745 UV clumps (located both in the disk and in the stripped tails) and 424 optical star-forming complexes (only in the tails). The luminosity and mass functions of these objects reveal that they form throughout the same mechanism observed and predicted in isolated disks and starburst galaxies, in which the neutral gas is thought to collapse into molecular gas clouds and eventually into the stellar clumps that we observe. This mechanism seems to hold even in the disturbed and stripped gas, far away from the galactic disk and embedded in the ICM. The H? luminosity-size relation of the RPS clumps, compared with literature, shows an enhanced L(H?) at a given size, if compared to clumps in isolated disks, but not as enhanced as the one observed in clumps of starburst galaxies. This enhancement is most likely caused by the early-stage effects of RPS, which is able to compress the gas. Finally, the morphology of the tail clumps shows the first systematic evidence of "fireballs", observed until now just in a dozen of clumps in stripped tails, in which young stars are displaced further away from the galactic disk than old stars with. This is a consequence of RPS, acting only on the gaseous component of the clumps, without affecting the stellar component.