The quest for hot gas in the halo of NGC 1511

¹ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
² XMM-Newton Science Operations Centre, Apartado 50727, 28080 Madrid, Spain
³ Science Operations & Data Systems Division, Research and Scientific Support Department of ESA, ESTEC, 2200 AG Noordwijk, The Netherlands
⁴ Dept. of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, USA
⁵ NASA/Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA

Corresponding author: M. Dahlem, Michael.Dahlem@csiro.au

Received: 2 January 2003
Accepted: 5 March 2003

Abstract

XMM-Newton observations of the starburst galaxy NGC 1511 reveal the presence of a previously unknown extended hot gaseous phase of its ISM, which partly extends out of the disk plane. The emission distribution is asymmetric, being brightest in the eastern half of the galaxy, where also radio continuum observations suggest the highest level of star formation. Spectral analysis of the integral 0.2–12 keV X-ray emission from NGC 1511 indicates a complex emission composition. A model comprising a power law plus thermal plasma component, both absorbed by foreground gas, cannot explain all details of the observed spectrum, requiring a third spectral component to be added. This component can be a second thermal plasma, but other spectral models can be fitted as well. Its X-ray properties characterize NGC 1511 as a starburst galaxy. The X-ray-to-infrared luminosity ratio is consistent with this result. Together with the X-ray data, XMM-Newton obtained UV images of NGC 1511, tracing massive stars heating the ambient gas, which is then seen in Hα emission. UV, Hα and near-infrared imagery suggest that NGC 1511 is disturbed, most likely by its two small companions, NGC 1511a and NGC 1511b.