Hot halo gas in the Virgo cluster galaxy NGC 4569

Abstract

Abstract.We have observed the Virgo cluster spiral NGC 4569 in X-rays with ROSAT (0.1-2.4 keV) and in the optical. From the PSPC image one can distinguish different components, like the dominant source in the nuclear region, the galactic disk, and a diffuse soft component extended to the west. This latter one coincides with a giant Hα structure. In both spectral ranges the structure reaches up to 9 kpc out of the disk. This coincidence, the soft X-ray energy distribution, and the existence of a central starburst in NGC 4569 let us conclude that the X-ray gas traces a large scale outflow from accumulating supernova explosions and stellar winds in the galactic center. The resulting physical properties of this X-ray halo are comparable to those derived from X-ray halos in edge-on galaxies, like e.g. NGC 253. We also discuss the influence of the intracluster medium on the observed X-ray and Hα morphology. The spectral 0.1-2.4 keV distribution of the central source and the X-ray-to-Hα luminosity ratio favour a supermassive star cluster at the very compact core rather than an accretion-powered active nucleus in agreement with the absence of a hard compact X-ray source in the ASCA band. The nearby Magellanic dwarf galaxy IC 3583 at a projected distance of only 30 kpc reveals an unresolved X-ray point source, several blue knots in the optical, and a narrow Hα spur, pointing toward NGC 4569, detected also in the B band image. This is an indication for ongoing star formation also in IC 3583. Some interaction with NGC 4569 will be discussed although the relative radial velocity between both objects of about 1300 km s −1 makes it rather unlikely.

Spectacular tails of ionized gas in the Virgo cluster galaxy NGC 4569

“…Rosat, XMM-Newton, Chandra X-ray, and VLA 1.4, 4.86 GHz radio continuum images of NGC 4569 show extended features that are perpendicular to the stellar disc of the galaxy (Tschoeke et al 2001;Chyzy et al 2006;Grier et al 2011;Wezgowiec et al 2011Wezgowiec et al , 2012. The extension of the hot gas traced by the 0.2−1 keV XMM-Newton X-ray image, however, is smaller than that of the ionized gas (Figs.…”

“…The spur of gas observed on the western side has a higher recessional velocity with respect to the nucleus of the galaxy and is thus an outflow. The nuclear outflow is probably powered by a nuclear starburst (Barth et al 1998;Maoz et al 1998;Barth & Shields 2000;Tschoeke et al 2001;Chyzy et al 2006). The spectral synthesis analysis of the nuclear HST spectra carried out by Barth & Shields (2000), who classified it as a typical LINER/HII transition nucleus, date the nuclear ( < ∼ 30 pc) starburst as ∼3−6 Myr (Barth & Shields 2000;Gabel & Bruhweiler 2002).…”

“…A contribution from an AGN cannot be fully excluded, given the presence of a compact source in the soft Chandra X-ray image of NGC 4569 (Grier et al 2011). A dominant AGN activity, however, is ruled out by the lack of a point-like nuclear source in the radio continuum (Hummel et al 1987;Neff & Hutchings 1992) and in the ROSAT X-ray hardband image of the galaxy (Tschoeke et al 2001). …”

Molecular gas in NUclei of GAlaxies (NUGA)

“…On larger scales Tschöke et al (2001) detected a large soft X-ray emitting region above the disk of NGC 4569 which implies a large energy input into the halo. Hensler et al (2003) reported on a bipolar outflow seen in X-rays and a giant outflow (∼10 kpc in length) to the western side of the galaxy in Hα (see also Bomans et al 2007, submitted).…”

“…The presence of a supergiant-dominated starburst was established by Keel (1996). Barth & Shields (2000) demonstrated that a starburst with a large population of very hot Wolf-Rayet stars could produce the observed spectrum of the nucleus and AGN activity is ruled out by X-ray (Terashima et al 2000;Tschöke et al 2001;Ho et al 2001) and radio observations (Hummel et al 1987;Neff & Hutchings 1992). Gabel & Bruhweiler (2002) showed that for the starburst to be the only source of photoionization (no AGN) extreme conditions are required, with ∼5 × 10 4 O and B stars squeezed into the inner 30 pc.…”