Integral field spectroscopy of the planetary nebula NGC 3242 and the puzzling nature of its low-ionization structures

Abstract

Context. We investigate the physico-chemical properties of the planetary nebula (PN) NGC 3242 in both 1D and 2D, using integral field unit (IFU) data. This PN has a complex morphology with multiple shells and contains a pair of structures with a lower degree of ionization compared to the main nebular components. The origin of these so-called low-ionization structures (LISs) remains a mystery. Aims. With the capabilities offered by IFU spectroscopy, we aim to gain a better understanding of the behavior of nebular properties in the LISs and examine the spatial distribution of physico-chemical parameters in NGC 3242. Methods. Data from the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT) were used in order to perform a spatially resolved physico-chemical analysis of NGC 3242. The analysis was performed both in 2D, based on emission line maps, as well as in 1D, via simulations of long-slit spectroscopy, with pseudo-slits. Results. Through the deeper investigation of MUSE data, we detected new structures perpendicular to the pair of LISs of NGC 3242, which are mainly seen in the light of [S III] and [N II]. In addition, two arc-like structures were revealed. Moreover, an inner jet-like structure was found through its [Fe III] emission. The interaction of the jet with the rim may be related to the formation of knots and blobs. The higher value of Te , is estimated from the [S III] diagnostic lines, followed by Te ([N II]), Te(H I) and, finally, Te (He I). In all cases, Te is higher at the inner nebular structures. Regarding electron density, ne , is lower at the LISs, while an increase is observed at the nebular rim. Diagnostic diagrams confirm that NGC 3242 is a highly ionized nebula. Moreover, for the first time, the MUSE data have unveiled the atomic line [C I] λ8727 in this PN, which is primarily emitted from the LISs. This finding suggests that these structures may consist of a molecular core surrounded by neutral and ionized gas.