Mon. Not. R. Astron. Soc., 464, 1833-1853 (2017/January-2)
Complexes of triggered star formation in supergiant shell of Holmberg II.
EGOROV O.V., LOZINSKAYA T.A., MOISEEV A.V. and SHCHEKINOV Y.A.
Abstract (from CDS):
We report a detailed analysis of all regions of current star formation in the walls of the supergiant H I shell (SGS) in the galaxy Holmberg II based on observations with a scanning Fabry-Perot interferometer at the Russian 6-m telescope. We compare the structure and kinematics of ionized gas with that of atomic hydrogen and with the stellar population of the SGS. Our deep Hα images and archival images taken by the Hubble Space Telescope demonstrate that current star formation episodes are larger and more complicated than previously thought: they represent unified star-forming complexes with sizes of several hundred pc rather than 'chains' of separate bright nebulae in the walls of the SGS. The fact that we are dealing with unified complexes is evidenced by identified faint shell-like structures of ionized and neutral gas which connect several distinct bright H II regions. Formation of such complexes is due to the feedback of stars with very inhomogeneous ambient gas in the walls of the SGS. The arguments supporting an idea about the triggering of star formation in SGS by the H I supershells collision are presented. We also found a faint ionized supershell inside the H I SGS expanding with a velocity of no greater than 10-15 km s–1. Five OB stars located inside the inner supershell are sufficient to account for its radiation, although a possibility of leakage of ionizing photons from bright H II regions is not ruled out as well.