A Chandra observation of M51: Active nucleus and nuclear outflows

We present a Chandra Advanced CCD Imaging Spectrometer (ACIS-S) observation of the nuclear region of the nearby spiral galaxy M51 (NGC 5194), which ha s a low-luminosity Seyfert 2 nucleus. The X-ray image shows the nucleus, so uthern extranuclear cloud, and northern loop, the morphology of the extende d emission being very similar to those seen in radio continuum and optical emission-line images. The X-ray spectrum of the nucleus is well represented by a model consisting of soft thermal plasma with kT approximate to 0.5 ke V, a very hard continuum, and an Fe K alpha emission line at 6.45 keV with an equivalent width of greater than 2 keV. The very strong Fe line and the flat continuum indicate that the nucleus is obscured by a column density in excess of 10(24) cm(-2) and that the spectrum is dominated by reflected em ission from cold matter near the nucleus. The X-ray spectra of the extranuc lear clouds are well fitted by a thermal plasma model with kT approximate t o 0.5 keV. This spectral shape and morphology strongly suggest that the clo uds are shock-heated by the bipolar outflow from the nucleus. The shock vel ocities of the extranuclear cloud and northern loop inferred from the tempe ratures of the X-ray gas are 690 and 660 km s(-1), respectively. By assumin g a steady state situation in which the emission of the extranuclear clouds is powered by the jets, the mechanical energy in the jets is found to be c omparable to the bolometric luminosity of the nucleus.