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

LAGOS, PATRICIO; PAPADEROS, POLYCHRONIS; GOMES, JEAN MICHEL; SMITH CASTELLI, ANALIA; VEGA, LUIS

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2014 vol. 569 p. 1 - 14

0004-6361

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 H II regions(GH IIRs). Our data also reveal some faint curved features in the BCD periphery that might be due to tidal perturbations or expandingionized-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 Hα and Hβ 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-ionizationHe II λ4686 emission line is detected only in the central part of HS 2236+1344. Similar to many BCDs with He II λ4686 emission, HS2236+1344 shows no Wolf-Rayet (WR) bump.