Extended HI halo in NGC 4449

Abstract

The Irregular galaxy of Magellanic type NGC 4449 has been observed with the Effelsberg radiotelescope in the HI 21 cm line. The emission was detected up to a distance of 14 galactic radii. It has been confirmed that the velocities in the halo increase, towers the South, i.e. in a direction opposite to the one observed over the galaxy itself. The systemic velocity is 214 km/s from which a distance of 3.7 Mpc (H₀= 75 km/s/Mpc) is derived. The HI mass is then 10⁹ M⊙ and the total mass, within 30', 2.1x10¹⁰ M⊙.