Spectroscopic mapping of the physical properties of supernova remnant N\,49

Abstract

Physical conditions inside a supernova remnant can vary significantly between different positions. However, typical observational data are integrated data or contemplate specific portions of the remnant. We study the spatial variation in the physical properties of the N\,49 supernova remnant based on a spectroscopic mapping of the whole nebula. Long-slit spectra were obtained with the slit ($\sim4\arcmin \times 1.03\arcsec$) aligned along the east-west direction from 29 different positions spaced by $2\arcsec$ in declination. A total of 3248 1D spectra were extracted from sections of $2\arcsec$ of the 2D spectra. More than 60 emission lines in the range 3550\,\AA{} to 8920\,\AA{} were measured in these spectra. Maps of the fluxes and of intensity ratios of these emission lines were built with a spatial resolution of $2\arcsec \times 2\arcsec$. An electron density map has been obtained using the [S\,{\sc ii}]\,$\lambda6716/\lambda6731$ line ratio. Values vary from $\sim$500\,cm$^{-3}$ at the northeast region to more than 3500 cm$^{-3}$ at the southeast border. We calculated electron temperature using line ratio sensors for the ions S$^{+}$, O$^{++}$, O$^{+}$, and N$^{+}$. Values are about 3.6$\times10^{4}$\,K for the O$^{++}$ sensor and about 1.1$\times10^{4}$\,K for other sensors. The H$\alpha$/H$\beta$ ratio map presents a ring structure with higher values that may result from collisional excitation of hydrogen. We detected an area with high values of [N\,{\sc ii}]\,$\lambda6583$/H$\alpha$ extending from the remnant center to its northeastern border, that can be indicating an overabundance of nitrogen in the area due to contamination by the progenitor star. We found a radial dependence in many line intensity ratio maps. We observed an increase toward the remnant borders of the intensity ratio of any two lines in which the numerator comes before in a sequence of lines.