Deep VLT spectroscopy of the blue compact dwarf galaxies Tol 1214-277 and Tol 65

Abstract

We present VLT spectroscopic observations with different spectral resolutions and different slit orientations of the two metal-deficient blue compact dwarf (BCD) galaxies Tol 1214-277 and Tol 65. The oxygen abundances in the brightest H II regions of Tol 1214-277 and Tol 65 are found to be 12 + log O/H = 7.55 ± 0.01 and 7.54 ± 0.01, or Z⊙/ 24***. The nitrogen-to-oxygen abundance ratios in the two galaxies are log N/O = -1.64 ± 0.03 and -1.60 ± 0.02 and lie in the narrow range found for other most metal-deficient BCDs. The helium mass fraction derived in several H II regions in both galaxies is consistent with a high primordial helium mass fraction, Yp ∼ 0.244. We confirm the detection of the high-ionization forbidden emission line [Fe V] λ4227 in the spectrum of Tol 1214-277. Additionally, weak [Ne IV] λ4725, [Fe VI] λ5146, λ5177, and [Fe VII] λ5721, λ6087 emission lines are detected in the high-resolution spectrum of Tol 1214-277. The detection of these lines implies the presence of hard radiation with photon energy in the range ∼4-8 Ryd. Emission lines are detected in the spectra of eight galaxies in the fields of Tol 1214-277 and Tol 65. Seven of these galaxies are background objects, while one galaxy has a redshift close to that of Tol 1214-277. Situated at a projected distance of ∼14.5 kpc from Tol 1214-277, this galaxy is probably a companion of the BCD.