Evidence for a Fast Soft X-ray Wind in M82 from XMM-RGS

Starburst wind models predict that metals and energy are primarily carried out of the disk by hot gas (T > 10^6 K), but the low energy resolution of X-ray CCD observations results in large uncertainties on the mass and energy loading. Here, we present evidence for a fast soft X-ray wind from the prototypical starburst galaxy M82 using deep archival observations from the Reflection Grating Spectrometer on XMM-Newton. After characterizing the complex line-spread function for the spatially extended outflow (4'), we perform emission-line fitting to measure the velocity dispersion, ₕ, from OVIII (0. 65, 0. 77 keV), NeX (1. 02 keV), and MgXII (1. 47 keV). For the T 3 10^6 K gas, OVIII yields a velocity dispersion of ₕ = 1160^+100-₉₀ km s^-1, implying a wind speed that is significantly above the escape velocity (v₄ₒ₂ 450 km s^-1). NeX (ₕ = 550^+130-₁₅₀ km s^-1) and MgXII (ₕ < 370 km s^-1) show less velocity broadening than OVIII, hinting at a lower wind speed or smaller opening angle on the more compact spatial scales traced by the T (0. 6 - 1) 10^7 K gas. Alternatively, these higher energy emission lines may be dominated by shock-heated gas in the interstellar medium. Future synthesis of these measurements with Performance Verification observations of the E = 2 - 12 keV wind in M82 from the Resolve microcalorimeter on the X-ray Imaging and Spectroscopy Mission will inform the phase structure and energy budget of the hot starburst wind.