Chemical enrichment of the complex hot ISM of the Antennae Galaxies

We present an analysis of the properties of the interstellar medium (ISM) in the merging pair of galaxies known as The Antennae (NGC 4038/39), performed using the deep coadded ∼411 ks Chandra ACIS-S data set. These deep observations and Chandra's high angular resolution allow us to investigate the properties of the hot ISM with unprecedented spatial and spectral resolution. Through a spatially resolved spectral analysis, we find a variety of temperatures (from 0.2 to 0.9 keV), densities (from 3 × 10 −2 to 3 × 10 −1 cm −3), and N H (from Galactic to a 2 × 10 21 cm −2). Metal abundances for Ne, Mg, Si, and Fe vary dramatically throughout the ISM from sub-solar values (∼0.2) up to ∼20–30 times solar. Measures for the hot-gas mass (∼10 7 M ⊙), cooling times (10 7 –10 8 yr), and pressure are derived. In the two nuclei the hot-gas pressure is significantly higher than the CO pressure, implying that shock waves may be driven into the CO clouds. Comparison of the abundances with the average stellar yields predicted by theoretical models of SN explosions points to SNe ot Type II as the main contributor of metals to the hot ISM. There is no evidence of any correlation between radio-optical star formation indicators and the metal abundances. Although uncertainties in the average density cannot exclude that mixing may have played some important role, the time required to produce the observed metal masses (3 Myr) suggests that the correlations are unlikely to be destroyed by the presence of efficient mixing. More likely a significant fraction of SN II ejecta may be in a cool phase, in grains, or escaping in the wind. – 2 –