Piecing together the puzzle of NGC 5253: abundances, kinematics and WR stars^⋆,⋆⋆

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
e-mail: mwestmoq@eso.org
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
⁴ Instituto de Astrofísica de Andalucía (CSIC), C/ Camino Bajo de Huétor 50, 18008 Granada, Spain

Received: 17 October 2012
Accepted: 10 December 2012

Abstract

We present Gemini-S/GMOS-IFU optical spectroscopy of four regions near the centre of the nearby (3.8 Mpc) dwarf starburst galaxy NGC 5253. This galaxy is famous for hosting a radio supernebula containing two deeply embedded massive super star clusters, surrounded by a region of enhanced nitrogen abundance that has been linked to the presence of Wolf-Rayet (WR) stars. We detected 11 distinct sources of red WR bump (C iv) emission over a 20′′ (~350 pc) area, each consistent with the presence of ~1 WCE-type star. WC stars are not found coincident with the supernebula, although WN stars have previously been detected here. We performed a multi-component decomposition of the Hα line across all four fields and mapped the kinematics of the narrow and broad (FWHM = 100−250 km s^-1) components. These maps paint a picture of localised gas flows, as part of multiple overlapping bubbles and filaments driven by the star clusters throughout the starburst. We confirm the presence of a strong Hα velocity gradient over ~4.″5 (~80 pc) coincident with the region of N/O enhancement, and high gas density known from previous study, and interpret this as an accelerating ionized gas outflow from the supernebula clusters. We measure the ionized gas abundances in a number of regions in the outer IFU positions and combine these with measurements from the literature to assess the radial abundance distribution. We find that the O/H and N/H profiles are consistent with being flat. Only the central 50 pc exhibits the well-known N/O enhancement, and we propose that the unusually high densities/pressures in the supernebula region have acted to impede the escape of metal-enriched hot winds from the star clusters and allow them to mix with the cooler phases, thus allowing these freshly processed chemicals to be seen in the optical.