Carbon Abundances in Starburst Galaxies of the Local Universe

The cosmological origin of carbon, the fourth most abundant element in the Universe, is not well known and matter of heavy debate. We investigate the behavior of C/O to O/H in order to constrain the production mechanism of carbon. We measured emission-line intensities in a spectral range from 1600 to 10000 \AA\ on Space Telescope Imaging Spectrograph (STIS) long-slit spectra of 18 starburst galaxies in the local Universe. We chose 9 strong lines over the wide spectral range observed and compared the measured intensities with those modeled by the photoionization code \cldy, using as ionizing source a theoretical spectrum obtained with the population synthesis code {\tt Starburst99}. We determined chemical abundances through traditional nebular analysis and through a Markov Chain Monte Carlo (MCMC) method. We obtained abundances comparable to those from our observations determined with the direct method. We analyzed the behavior of our sample in the [C/O] versus [O/H] diagram with respect to other objects such as DLAs, neutral ISM measurements, and disk and halo stars, finding that each type of object is located in a specific region of the diagram. This result confirms that C/O can in fact work as an efficient ``evolution clock": older objects have an enrichment of carbon perhaps due to Population III stars, then the nucleosynthesis of carbon and oxygen falls as Population II takes over.