The multi-phase gaseous halos of star forming late-type galaxies - I. XMM-Newton observations of the Hot Ionized Medium

TL;DR

This paper reports XMM-Newton X-ray observations of diffuse hot ionized gas halos in nine nearby star-forming edge-on spiral galaxies, revealing correlations with ionized gas, cosmic rays, and star formation activity, and providing new high-resolution detections.

Contribution

First high-resolution X-ray detections of extended hot gas halos in multiple star-forming galaxies, linking these halos to star formation and multi-phase interstellar medium components.

Findings

Diffuse X-ray halos detected in 8 of 9 galaxies.

Halo properties decrease with distance from the disk.

Star formation activity correlates with halo creation.

Abstract

This study presents first results from an X-ray mini-survey carried out with XMM-Newton to investigate the diffuse Hot Ionized Medium in the halos of nine nearby star-forming edge-on spiral galaxies. Diffuse gaseous X-ray halos are detected in eight of our targets, covering a wide range of star formation rates from quiescent to starburst cases. For four edge-on spiral galaxies, namely NGC3044, NGC3221, NGC4634, and NGC5775, we present the first published high resolution/sensitivity detections of extended soft X-ray halos. EPIC X-ray contour maps overlaid onto Halpha imaging data reveals that in all cases the presence of X-ray halos is correlated with extraplanar Diffuse Ionized Gas. Moreover, these halos are also associated with non-thermal cosmic ray halos, as evidenced by radio continuum observations. Supplemental UV-data obtained with the OM-telescope at 210nm show Diffuse Ionized Gas to be well associated with UV emission originating in the underlying disk. Beside NGC891, NGC4634 is the second non-starburst galaxy with a diffuse soft X-ray halo (|z|<4kpc). In case of NGC3877, for which we also present the first high resolution X-ray imaging data, no halo emission is detectable. EPIC pn spectra (0.3-12keV) of the diffuse X-ray emission are extracted at different offset positions from the disk, giving evidence to a significant decrease of gas temperatures, electron densities, and gas masses with increasing distance to the plane. A comparison between dynamical and radiative cooling time scales implies that the outflow in all targets is likely to be sustained. We find very strong indications that spatially correlated multi-phase gaseous halos are created by star forming activity in the disk plane.