A hot bubble at the centre of M 81

Abstract

Context. 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. 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 Müller et al. 2011, MNRAS, 413, 149). Methods. 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 > 43 500 K that is associated with strong emission of [N II]λ5755 Å and a high [O I]λ6300/Hα ratio; the bubble displays a bluish continuum, surrounded by a thin shell of Hα + [N II] emission. We also reinterpret the outflow found by Schnorr Müller 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.

Digging process in NGC 6951: the molecular disc bumped by the jet

“…If this result is, indeed, indicative of shock waves, there is no strong evidence of any young stellar population in the nucleus (van der Laan et al 2013), which would be related with supernova remnants and stellar winds. A similar structure, of comparable dimension, was found near the nucleus in M81 (Ricci et al 2015) and, on a smaller scale, in stellar clusters at the centre of the Milky Way, as the Arches Cluster (Yusef-Zadeh Figure 18. Left: tomogram 2 obtained with PCA tomography of the GMOS data cube, with the cones corresponding to positive and negative weight, shown in red and blue, respectively.…”

Inflowing gas in the central parsec of M81

“…The summation was performed over the velocity span of the broad Hα line depicted in Figure 15. The observed profile has a flat top that can be reproduced in the model line profiles by creating a biconical-shaped cavity that is expected to be occupied by the jets, evidence for which has been seen in the radio (Martí-Vidal et al 2011) and in the visible (Ricci et al 2015). At the expense of one more parameter, a bi-conical cavity is invoked in spherical coordinates by restricting the polar angle, θ such that -0.85π/2 ≤ θ ≤ 0.85π/2 for all azimuthal angles φ so that 0 ≤ φ ≤ 2π.…”

“…The resulting geometry for the Hα emitting region is illustrated in Figure 16 wherein the azimuthal axis of symmetry is perpendicular to the line-of-sight. Observationally, M81* has what appears to be a one-sided radio jet, the inclination angle of which is undetermined (Martí-Vidal et al 2011;Bietenholz et al 2000Bietenholz et al , 1996, but it is quite likely to be small as the one-sided nature of the radio-jet has been attributed to Doppler boosting by Ricci et al (2015) based on a re-examination of the Schnorr Müller et al (2011) dataset. More complicated models for the Hα emitting geometry could be contrived, but at the expense of additional free parameters.…”

CAHA/PPAK Integral-field Spectroscopic Observations of M81 -- I. Circumnuclear ionized gas

“…Alternatively, a bi-polar inflow along the disk rotation axis would produce similar velocity patterns, which, however, appears physically implausible. Support for an outflow comes from Schnorr Müller et al (2011) and Ricci et al (2015a), who both analyzed the velocity field in the central 10 pc using the principle component analysis (PCA) tomography (Steiner et al 2009) Res. (PC 4) as a conical outflow of ionized gas.…”

“…GMOS IFS observations have found signatures of both an inflow of ionized gas at a rate of 3 × 10 −3 M ⊙ yr −1 and an outflow vertical to a rotating ionized gas disk in the central 120 pc×250 pc region (Schnorr Müller et al 2011). This outflow was reinterpreted by Ricci et al (2015a) as in line with the radio jet. More recently, a high-velocity outflow of hot gas is detected in the central 40 pc region with Chandra X-ray spectroscopy (Shi et al 2021), which is most likely driven by the hot accretion flow onto the SMBH.…”