4.3. NGC 4636

A wealth of X-ray data has been accumulated for this X-ray bright galaxy since Einstein Observatory times, that indicate a very extended distribution of the X-ray emission, due almost entirely to hot gas at an average temperature of ~ 1 keV and total luminosity of L_X ~ 2 × 10⁴¹ erg s^-1 [Trinchieri et al. 1994, Matsushita et al. 1998, Buote, 2000]. From an Einstein HRI observation, [Stanger & Warwick, 1986] had already proposed an asymmetric gas distribution at small radii. Chandra data now clearly show symmetric, 8 kpc long, clearly defined spiral-like twisted structures in the inner few arcmin region of this galaxy (Fig. 4.3, [Jones et al.2002]), coupled with a complex temperature structure of the gas, a weak but measurable temperature gradient (but no cooling flow!) in the inner regions and a number of discrete spectral lines measured with XMM-Newton data [Xu et al. 2002]. To date there are no reports of a close morphological relation between the hot and the warm phases, although H is detected in this object [Demoulin-Ulrich et al. 1984] with chaotic gas kinematics and with evidence for a kinematically distinct inner region like NGC 5846 [Caon et al. 2000]. jonesetal propose that the X-ray morphology is formed as a result of shocks driven by a nuclear outburst in the recent past. These outbursts would also have implications both in the accumulation of material in the galaxy's center, and in the fueling of a central AGN.

Figure 7. Right (from Jones et al. [2002]): Full resolution ACIS-S image of the central regions of NGC 4636 in the 0.5-2.0 keV energy range. A plus sign marks the galaxy center.