Breakout: The Origin of Faint Extended Broad Emission Lines Associated with Giant Extragalactic H II Regions

摘要

The faint extended broad (≥1000 km s~-1) optical emission lines associated with giant H II regions are shown here to be produced in a shell of ISM material smoothly accelerated soon after breakout. Two-dimensional calculations of remnants caused by a strong energy deposit in a low metal abundance ISM are here shown to undergo breakout once encountering a steep density gradient, leading to a fast-moving shell capable of producing the broad and faint emission lines. Energetic sources lead to fast, thick, and hot shells, and when evolving in a low-metallicity ISM, to quasi-adiabatic shells that strongly delay their fragmentation owing to Rayleigh-Taylor instabilities.