The Hot Interstellar Medium of the Interacting Galaxy NGC 4490

Abstract

We present an analysis of the hot interstellar medium (ISM) in the spiral galaxy NGC 4490, which is interacting with the irregular galaxy NGC 4485, using ~100ks of Chandra ACIS-S observations. The high angular resolution of Chandra enables us to remove discrete sources and perform spatially resolved spectroscopy for the star forming regions and associated outflows, allowing us to look at how the physical properties of the hot ISM such as temperature, hydrogen column density and metal abundances vary throughout these galaxies. We find temperatures of >0.41 keV and 0.85 +0.59/-0.12 keV, electron densities of >1.87 eta^(-1/2) x 10^(-3) cm^(-3) and 0.21 +0.03/-0.04 eta^(-1/2) x 10^(-3) cm^(-3), and hot gas masses of >1.1 eta^(1/2) x 10^7 M_{\odot} and ~3.7 eta^(1/2) x 10^7 M_{\odot} in the plane and halo of NGC 4490 respectively, where eta is the filling factor of the hot gas. The abundance ratios of Ne, Mg and Si with respect to Fe are found to be consistent with those predicted by theoretical models of type II supernovae. The thermal energy in the hot ISM is ~5% of the total mechanical energy input from supernovae, so it is likely that the hot ISM has been enriched and heated by type II supernovae. The X-ray emission is anticorrelated with the H-alpha and mid-infrared emission, suggesting that the hot gas is bounded by filaments of cooler ionized hydrogen mixed with warm dust.