The multi-phase gaseous halos of star forming late-type galaxies

Free access article

Issue		A&A Volume 448, Number 1, March II 2006


Page(s)		43 - 75
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20052936

A&A 448, 43-75 (2006)
DOI: 10.1051/0004-6361:20052936

I. XMM-Newton observations of the hot ionized medium

R. Tüllmann¹, W. Pietsch², J. Rossa³, D. Breitschwerdt⁴ and R.-J. Dettmar¹

¹ Astronomisches Institut, Ruhr-Universität Bochum, 44780 Bochum, Germany
    e-mail: [tullmann;dettmar]@astro.rub.de
² Max-Planck Institut für extraterrestrische Physik, Geissenbachstrasse, 85748 Garching, Germany
    e-mail: wnp@mpe.mpg.de
³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
    e-mail: jrossa@stsci.edu
⁴ Institut für Astronomie, Türkenschanzstrasse 17, 1180 Wien, Austria
    e-mail: breitschwerdt@astro.univie.ac.at

(Received 25 February 2005 / Accepted 25 September 2005)

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 NGC 3044, NGC 3221, NGC 4634, and NGC 5775, we present the first published high resolution/sensitivity detections of extended soft X-ray halos. EPIC X-ray contour maps overlaid onto H $\alpha$ 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 210 nm show Diffuse Ionized Gas to be well associated with UV emission originating in the underlying disk. Beside NGC 891, NGC 4634 is the second non-starburst galaxy with a diffuse soft X-ray halo ( $\vert z\vert\le 4$ kpc). In case of NGC 3877, for which we also present the first high resolution X-ray imaging data, no halo emission is detectable. EPIC pn spectra (0.3-12 keV) 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. In a forthcoming paper, we will present multi-frequency luminosity relations and evaluate key parameters which might trigger the formation of multi-phase galaxy halos.

Key words: galaxies: halos -- galaxies: ISM -- galaxies: spiral -- X-rays: galaxies -- X-rays: ISM

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