The relative impact of photoionizing radiation and stellar winds on different environments

ABSTRACT Photoionizing radiation and stellar winds from massive stars deposit energy and momentum into the interstellar medium (ISM). They might disperse the local ISM, change its turbulent multi-phase structure, and even regulate star formation. Ionizing radiation dominates the massive stars’ energy output, but the relative effect of winds might change with stellar mass and the properties of the ambient ISM. We present simulations of the interaction of stellar winds and ionizing radiation of 12, 23, and 60 M⊙ stars within a cold neutral (CNM, n0 = 100 cm−3), warm neutral (WNM, n0 = 1, 10 cm−3), or warm ionized (WIM, n0 = 0.1 cm−3) medium. The flash simulations adopt the novel tree-based radiation transfer algorithm TreeRay. With the On-the-Spot approximation and a temperature-dependent recombination coefficient, it is coupled to a chemical network with radiative heating and cooling. In the homogeneous CNM, the total momentum injection ranges from 1.6 × 104 to 4 × 105 M⊙ km s−1 and is always dominated by the expansion of the ionized HII region. In the WIM, stellar winds dominate (2 × 102 to 5 × 103 M⊙ km s−1), while the input from radiation is small (∼ 102 M⊙ km s−1). The WNM (n0 = 1 cm−3) is a transition regime. Energetically, stellar winds couple more efficiently to the ISM (∼ 0.1 percent of wind luminosity) than radiation (< 0.001 percent of ionizing luminosity). For estimating the impact of massive stars, the strongly mass-dependent ratios of wind to ionizing luminosity and the properties of the ambient medium have to be considered.