Paper detail

X-ray narrow emission lines from the nuclear region of NGC 1365

NGC 1365 is a Seyfert 2 galaxy with a starburst ring in its nuclear region. In this work we look at the XMM Reflection Grating Spectrometer (RGS) data from four 2012-13, three 2007 and two 2004 observations of NGC 1365. We characterise the narrow-line emitting gas visible by XMM RGS and make comparisons between the 2012-13 spectra and those from 2004-07, already published. This source is usually absorbed within the soft X-ray band, with a typical neutral column density of >1.5 x 10$^{23}$ cm$^{-2}$, and only 1 observation of the 9 we investigate shows low enough absorption for the continuum to emerge in the soft X-rays. We stack all observations from 2004-07, and separately three of the four observations from 2012-13, analysing the less absorbed observation separately. We first model the spectra using gaussian profiles representing the narrow line emission. We fit physically motivated models to the 2012-13 stacked spectra, with collisionally ionised components representing the starburst emission and photoionised line emission models representing the AGN line emission. The collisional and photoionised emission line models are fitted together on top of a physical continuum and absorption model. The X-ray narrow emission line spectrum of NGC 1365 is well represented by a combination of two collisionally ionised and three photoionised phases of emitting gas, all with higher than solar nitrogen abundances. This physical model was fitted to the 2012-13 stacked spectrum, and yet also fits well to the 2004-07 stacked spectrum, without changing any characteristics of the emitting gas phases. Our 2004-07 results are consistent with previous emission line work using these data, with 5 additional emission lines detected in both this and the 2012-13 stacked spectra. We also estimate the distance of the X-ray line-emitting photoionised gas from the central source to be <300 pc.