ASCA OBSERVATIONS OF THE STARBURST-DRIVEN SUPERWIND GALAXY NGC 2146: BROADBAN (0.6-9 keV) SPECTRAL PROPERTIES

摘要

We report ASCA GIS and SIS observations of the nearby (D = 11.6 Mpc), nearly edge-on, starburst galaxy NGC 2146. These X-ray spectral data complement ROSAT PSPC and HRI imaging already dis- cussed in the literature. The broadband (0.6-9 keV) X-ray spectrum of NGC 2146 is best described by a two-component model, the soft X-ray emission being modeled by a Raymond-Smith thermal plasma model with a temperature of kT ~ 0.8 keV, while the hard X-ray emission is modeled by a thermal plasma model with kT ~ 8 keV, or by a power-law model with a photon index of ~ 1.7. We do not find compelling evidence of substantial excess absorption above the Galactic value. The total luminosities of NGC 2146 in the soft (0.52.0 keV), hard (210 keV), and broad (0.510.0 keV) energy bands are ~ l.3 x 10~40, ~l.8 x 10~40, and ~3.1 x 10~40 ergs s-1 , respectively. The soft and hard thermal com- ponents provide about 30 and 70, respectively, of the total luminosity in the 0,5-2.0 keV energy band, while in the 2-10 keV energy range only the hard component plays a major role. The spectral results allow us to set tighter constraints on the starburst-driven superwind model which we show can satisfactorily account for the luminosity, mass, and energy content represented by the soft X-ray spectral component. We estimate that the mass outflow rate (~9 Mo yr-1) is about an order of magnitude greater than the predicted rate at which supernova and stellar winds return mass into the interstellar medium, and therefore we argue that the flow is strongly ``mass loaded'' with material in and around the starburst. Th