Astrophys. J., 700, 654-678 (2009/July-3)
Keck HIRES spectroscopy of extragalactic H II regions: C and O abundances from recombination lines.
ESTEBAN C., BRESOLIN F., PEIMBERT M., GARCIA-ROJAS J., PEIMBERT A. and MESA-DELGADO A.
Abstract (from CDS):
We present very deep spectrophotometry of 14 bright extragalactic H II regions belonging to spiral, irregular, and blue compact galaxies. The data for 13 objects were taken with the High Resolution Echelle Spectrometer on the Keck I telescope. We have measured C II recombination lines in 10 of the objects and O II recombination lines in eight of them. We have determined electron temperatures from line ratios of several ions, especially those of low ionization potential. We have found a rather tight linear empirical relation between Te([N II]) and Te([O III]). We have found that O II lines give always larger abundances than [O III] lines. Moreover, the difference of both O++ abundance determinations–the so-called abundance discrepancy factor–is very similar in all the objects, with a mean value of 0.26±0.09 dex, independent of the properties of the H II region and of the parent galaxy. Using the observed recombination lines, we have determined the O, C, and C/O radial abundance gradients for three spiral galaxies: M33, M101, and NGC 2403, finding that C abundance gradients are always steeper than those of O, producing negative C/O gradients across the galactic disks. This result is similar to that found in the Milky Way and has important implications for chemical evolution models and the nucleosynthesis of C.
galaxies: abundances - galaxies: individual (M31, M33, M83, M101, NGC 1741, NGC 2366, NGC 2403, NGC 4395, NGC 4861) - galaxies: ISM - galaxies: spiral - H II regions
VizieR on-line data:
<Available at CDS (J/ApJ/700/654): sources.dat tab234.dat>
K932 is [WB92a] 932 and H1013 is HGGK 1013 in Simbad.
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