On the properties of the interstellar medium in extremely metal-poor blue compact dwarf galaxies:
GMOS-IFU spectroscopy and SDSS photometry of the double-knot galaxy HS 2236+1344

P. Lagos, P. Papaderos, J. M. Gomes, A. V. Smith Castelli, L. R. Vega

Abstract
Aims. The main goal of this study is to carry out a spatially resolved investigation of the warm interstellar medium (ISM) in the extremely metal-poor Blue Compact Dwarf (BCD) galaxy HS 2236+1344. Special emphasis is laid on the analysis of the spatial distribution of chemical abundances, emission-line ratios and kinematics of the ISM, and to the recent star-forming (SF) activity in this galaxy.
Methods. This study is based on optical integral field unit spectroscopy data from Gemini Multi-Object Spectrograph (GMOS) at the Gemini North telescope and archival Sloan Digital Sky Survey (SDSS) images. The galaxy has been observed at medium spectral resolution (R ~ 4000) over the spectral range from ~ 4300 Å to 6800 Å. The data were obtained in two different positions across the galaxy, obtaining a total 4''×8'' field which encompasses most of its ISM.
Results. Emission-line maps and broad-band images obtained in this study indicate that HS 2236+1344 hosts three Giant Hii regions (GHiiRs). Our data also reveal some faint curved features in the BCD periphery that might be due to tidal perturbations or expanding ionized-gas shells. The ISM velocity field shows systematic gradients along the major axis of the BCD, with its south-eastern and north-western half differing by ~80 km/s in their recessional velocity. The Ha and Hß equivalent width distribution in the central part of HS 2236+1344 is consistent with a very young (~3 Myr) burst. Our surface photometry analysis indicates that the ongoing starburst provides ~50% of the total optical emission, similar to other BCDs. It also reveals an underlying lower-surface brightness component with moderately red colors, which suggest that the galaxy has undergone previous star formation. We derive an integrated oxygen abundance of 12+log(O/H)=7.53±0.06 and a nitrogen-to-oxygen ratio of log(N/O)=-1.57±0.19. Our results are consistent, within the uncertainties, with a homogeneous distribution of oxygen and nitrogen within the ISM of the galaxy. The high-ionization He ii λ4686 emission line is detected only in the central part of HS 2236+1344. Similar to many BCDs with He ii λ4686 emission, HS 2236+1344 shows no Wolf-Rayet (WR) bump.

Keywords
Galaxies: individual: HS 2236+1344 – Galaxies: dwarf – Galaxies: abundances – Galaxies: ISM – Galaxies: star formation – Galaxies: photometry

Astronomy and Astrophysics
Volume 569, Page A110_1
September 2014

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