Dust and star formation in the centre of NGC 3311
  NGC 3311 is the central galaxy of the Hydra I galaxy cluster. It has a hot
interstellar medium and hosts a central dust lane with emission lines. These
dust lanes are frequent in elliptical galaxies, but the case of NGC 3311 might
be particularly interesting for problems of dust lifetime and the role of cool
gas in the central parts. We aim to use archival HST images and MUSE data to
investigate the central dust structure of NGC 3311. We used the tool PyParadise
to model the stellar population and extract the emission lines. The HST/ACS
colour map reveals the known dust structures, but also blue spots, which are
places of strong line emission. A dusty 'mini-jet' emanates from the centre.
The distribution of the emission line gas matches the dust silhouette almost
exactly. Close to the brightest Halpha emission, the ratio [NII]/Halpha
resembles that of HII-regions; in the outer parts, [NII] gets stronger and is
similar to LINER-like spectra. The gas kinematics is consistent with that of a
rotating disc. The Doppler shifts of the strongest line emissions, which
indicate the areas of highest star formation activity, smoothly fit into the
disc symmetry. The metallicity is supersolar. The presence of neutral gas is
indicated by the fit residuals of the stellar NaI D absorption line, which we
interpret as interstellar absorption. We estimate the mass of the neutral gas
to be of the order of the X-ray mass. The dynamical mass infers a stellar
population of intermediate age, whose globular clusters have already been
identified. Our findings can be harmonised in a scenario in which the star
formation is triggered by the accretion of cold gas onto a pre-existing
gas/dust disc or ring. Newly produced dust then contributes to the longevity of
the dust.
