A high resolution X-ray spectrum of the nearby LINER M81

1. A high resolution X-ray spectrum of the nearby LINER M81 M. J. Page1, A. A. Breeveld1 and the RGS Consortium 1Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT Here we present results from the analysis of the XMM-Newton RGS observations of the spiral LINER galaxy M81. The excellent RGS data clearly show the presence of emission lines, as well as continuum emission from the active nucleus. The emission lines are significantly broader than the RGS point-source spectral resolution, and appear to originate from multi-temperature (0.15-0.8 keV) collisionally ionized gas in a region of at least an arcminute across. Fig 2. Spatially extended emission line gas: emission lines are seen an arcminute away from the nucleus in the cross dispersion direction. Fig 1. The RGS spectrum with a power law + 3 temp Mekal model in red. Prominent emission lines are marked. M81 is a nearby spiral galaxy hosting a low luminosity Seyfert nucleus. ROSAT and Chandra data show apparently diffuse emission associated with the bulge, extending over a few arcminutes. Later, ROSAT, BBXRT, ASCA and SAX spectra suggested a soft thermal component at <1keV in addition to the absorbed power law from the nucleus. M81 was observed by XMM in April 2001 for 138ks; the RGS data are shown in Fig.1. The continuum from the AGN at the heart of M81 dominates the spectrum. A good fit is obtained with a simple power law model absorbed by an intrinsic cold column of 6.1020cm-2. The lines, and in particular O VIII Ly, are considerably broader than one expects from the RGS line spread function from a point source. Figure 2 shows that the emission line gas is actually spatially extended by more than an arcminute. Fig 3. shows a fit to the He-like Oxygen triplet. These lines are consistent with a purely collisionally ionized, low density plasma (ne~1010 cm-3 ). A 3-temperature Mekal plasma model provides a good fit to the emission lines (see Fig. 1). These data show that the emission lines come from the hot interstellar medium in the bulge region of M81, and are not powered by the nucleus. Fig 3. Fit to the O VII triplet. The line ratios (confidence contours) are consistent with collisional ionization.