Searching for Star Formation Outside Galaxies: Multiwavelength Analysis of the Intragroup Medium of HCG100

Abstract

We used multiwavelength data (HI, FUV, NUV, R) to search for evidence of star formation in the intragroup medium of the Hickson Compact Group 100. We find that young star-forming regions are located in the intergalactic HI clouds of the compact group which extend to over 130 kpc away from the main galaxies. A tidal dwarf galaxy candidate is located in the densest region of the HI tail, 61 kpc from the brightest group member and its age is estimated to be only 3.3 Myr. Fifteen other intragroup HII regions and TDG candidates are detected in the GALEX FUV image and within a field 10'x10' encompassing the HI tail. They have ages <200 Myr, HI masses of 10^(9.2-10.4) Msun, 0.001< SFR <0.01 Msun yr^-1, and stellar masses 10^4.3--10^6.5 Msun. The HI clouds to which many of them are associated have column densities about one order of magnitude lower than N(HI)~10^21 cm^-2.