2015A&A...576A..58R

Messier 81 has the nearest active nucleus with broad Hα emission. A detailed study of this galaxy's centre is important for understanding the innermost structure of the AGN phenomenon. Our goal is to seek previously undetected structures using additional techniques to reanalyse a data cube obtained with the GMOS-IFU installed on the Gemini North telescope (Schnorr Mueller et al. 2011MNRAS.413..149S). We analysed the data cube using techniques of noise reduction, spatial deconvolution, starlight subtraction, PCA tomography, and comparison with HST images. We identified a hot bubble with T>43500K that is associated with strong emission of [NII]λ5755Å and a high [OI]λ6300/Hα ratio; the bubble displays a bluish continuum, surrounded by a thin shell of Hα+[NII] emission. We also reinterpret the outflow found by Schnorr Mueller et al. (2011MNRAS.413..149S), showing that the blueshifted cone nearly coincides with the radio jet, as expected. We interpret the hot bubble as having been caused by post starburst events that left one or more clusters of young stars, similar to the ones found at the centre of the Milky Way, such as the Arches and the IRS 16 clusters. Shocked structures from combined young stellar winds or supernova remnants are probably the cause of this hot gas and the low ionization emission.