Balmer and Paschen jump temperature determinations in low-metallicity emission-line galaxies

Abstract

We have used the Balmer and Paschen jumps to determine the temperatures of the H+ zones of a total sample of 47 H II regions. The Balmer jump was used on MMT spectrophotometric data of 22 low-metallicity H II regions in 18 blue compact dwarf (BCD) galaxies and of one H II region in the spiral galaxy M101. The Paschen jump was used on spectra of 24 H II emission-line galaxies selected from the Data Release 3 of the Sloan Digital Sky Survey (SDSS). To derive the temperatures, we have used a Monte Carlo technique varying the electron temperature in the H+ zone, the extinction of the ionized gas and that of the stellar population, the relative contribution of the ionized gas to the total emission and the star formation history to fit the spectral energy distribution of the galaxies. For the MMT spectra, the fit was done in the wavelength range of 3200 - 5200A which includes the Balmer discontinuity, and for the SDSS spectra, in the wavelength range of 3900 - 9200A which includes the Paschen discontinuity. We find for our sample of H II regions that the temperatures of the O+2 zones determined from the nebular to auroral line intensity ratio of doubly ionized oxygen [O III] (4959+5007)/4363 do not differ, in a statistical sense, from the temperatures of the H+ zones determined from fitting the Balmer and Paschen jumps and the SEDs. We cannot rule out small temperature differences of the order of 3-5%.