We present new, deep H i line and 20‐cm radio‐continuum data of the very puzzling blue compact dwarf galaxy NGC 5253, obtained with the Australia Telescope Compact Array as part of the ‘Local Volume H i Survey’ (LVHIS). Our low‐resolution H i maps show, for the first time, the disturbed H i morphology that NGC 5253 possesses, including tails, plumes and detached H i clouds. The high‐resolution map reveals an H i plume at the SE and an H i structure at the NW that surrounds an Hα shell. This latter structure is related to an expanding bubble in the interstellar medium (ISM), but it will almost certainly not originate a galactic wind. We confirm that the kinematics of the neutral gas in NGC 5253 are highly perturbed and do not follow a rotation pattern. We discuss the outflow and infall scenarios to explain such disturbed kinematics, analyse the environment in which NGC 5253 resides and compare its properties with those observed in similar star‐forming dwarf galaxies. The radio‐continuum emission of NGC 5253 is resolved and associated with the intense star‐forming region located at the centre of the galaxy. We complete the analysis using multiwavelength data extracted from the literature, which include X‐ray, Galaxy Evolution Explorer (GALEX) far‐ultraviolet, optical B and R band and Hα, near‐infrared H band, and far‐infrared data. We estimate the star formation rate using this multiwavelength approach, and compare the results with other galaxy properties. NGC 5253 does not satisfy the Schmidt–Kennicutt law of star formation, has a very low H i mass‐to‐light ratio when comparing with its stellar mass and seems to be slightly metal‐deficient in comparison with starbursts of similar baryonic mass. Taking into account all available multiwavelength data, we conclude that NGC 5253 is probably experiencing the infall of a diffuse, low‐metallicity H i cloud along the minor axis of the galaxy. The infall of this independent H i cloud is comprising the ISM and triggering the powerful starburst we see in NGC 5253. The tidally disturbed material observed at the east and north of the galaxy is a consequence of this interaction, which probably started more than 100 Myr ago. The origin of this H i cloud may be related with a strong interaction between NGC 5253 and the late‐type spiral galaxy M83 in the past.

A faint new radio source has been detected in the nuclear region of the starburst galaxy M82 using Multi-Element Radio-Linked Interferometer Network radio observations designed to monitor the flux density evolution of the recent bright supernova SN 2008iz. This new source was initially identified in observations made between 2009 May 1 and 5 but had not been present in observations made 1 week earlier, or in any previous observations of M82. In this Letter, we report the discovery of this new source and monitoring of its evolution over its first 9 months of existence. The true nature of this new source remains unclear, and we discuss whether this source is an unusual and faint supernova, a supermassive black hole associated with the nucleus of M82 or intriguingly the first detection of radio emission from an extragalactic microquasar.

Context. Outflows powered by the injection of kinetic energy from massive stars can strongly affect the chemical evolution of galaxies, in particular of dwarf galaxies, as their lower gravitational potentials enhance the chance of a galactic wind. Aims. We therefore performed a detailed kinematic analysis of the neutral and ionised gas components in the nearby star-forming irregular dwarf galaxy NGC 4861. Similar to a recently published study of NGC 2366, we want to make predictions about the fate of the gas and to discuss some general issues about this galaxy. Methods. Fabry-Perot interferometric data centred on the Hα line were obtained with the 1.93 m telescope at the Observatoire de Haute-Provence. They were complemented by H i synthesis data from the VLA. We performed a Gaussian decomposition of both the Hα and the H i emission lines in order to search for multiple components indicating outflowing gas. The expansion velocities of the detected outflows were compared to the escape velocity of NGC 4861, which was modelled with a pseudo-isothermal halo.Results. Both in Hα and H i the galaxy shows several outflows, three directly connected to the disc and probably forming the edges of a supergiant shell, and one at kpc-distance from the disc. We measured velocity offsets of 20 to 30 km s −1 , which are low in comparison to the escape velocity of the galaxy and therefore minimise the chance of a galactic wind.