A hot bubble at the centre of M81

TL;DR

This study reveals a hot, high-temperature bubble at the center of M81, likely caused by post-starburst activity and stellar winds, using advanced data analysis techniques on GMOS-IFU observations.

Contribution

The paper introduces the detection of a hot bubble in M81's nucleus using novel data analysis methods, providing new insights into the galaxy's central structure.

Findings

Identification of a hot bubble with T > 43500 K

Association of the bubble with strong [N II] and [O I] emission

Reinterpretation of the outflow as aligned with the radio jet

Abstract

Context. Messier 81 has the nearest active nucleus with broad H$\alpha$ emission. A detailed study of this galaxy's centre is important for understanding the innermost structure of the AGN phenomenon. Aims. 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 M\"uller et al. 2011). Method. We analysed the data cube using techniques of noise reduction, spatial deconvolution, starlight subtraction, PCA tomography, and comparison with HST images. Results. We identified a hot bubble with T $>$ 43500 K that is associated with strong emission of [N II]$\lambda$5755\AA\ and a high [O I]$\lambda$6300/H$\alpha$ ratio; the bubble displays a bluish continuum, surrounded by a thin shell of H$\alpha$ + [N II] emission. We also reinterpret the outflow found by Schnorr M\"uller et al. (2011) showing that the blueshifted cone nearly coincides with the radio jet, as expected. Conclusions. 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.