Discovery of a galactic wind in the central region of M100

Abstract

We report the discovery of a galactic wind in the central region of the galaxy M100. This result is based on a careful 2D spectroscopic study performed on observations made with the fibre system INTEGRAL on the WHT. The primary evidence of the wind is the presence of blueshifted interstellar NaD absorption lines. The velocity field of the absorbers show a clear rotation pattern but globally blueshifted ($\sim$ -115 km/s) with respect to the systemic velocity of the galaxy. The emission lines also present a blueward component arising from the ionized gas phase of the galactic wind. The velocity field of the ionized gas wind component shows no evidences of rotation but exhibits a pattern that can be interpreted in terms of the projection of an outflowing cone or shell. The wind component has [NII]/H$α$ ratios of about 1.8, typical of shock ionization. The ionized component of the wind can be identified with an expanding shell of shocked gas, and the neutral component with disk gas entrained in the wind at the interface of the expanding shell with the galactic ISM. The galactic wind seems to be driven uniquely by the nuclear starburst. Our analysis indicates that a non negligible fraction of the wind material might escape to the IGM. In this case, if the wind detected in M100 were representative of similar phenomena in other galaxies with low to moderate activity, the current estimates of metal and dust content of the IGM might be drastically underestimated.