Detalles de publicación
PP 06039
The localized chemical pollution in NGC 5253 revisited: Results from deep echelle spectrophotometry
(1) Instituto de Astrofísica de Canarias
(2) Instituto de Astronomía, UNAM, Mexico
(3) Instituto de Astrofísica, Óptica y Electrónica, Puebla, Mexico
We present echelle spectrophotometry of the blue compact dwarf galaxy (BCDG)
NGC~5253. The data have been taken with the Very Large Telescope UVES echelle
spectrograph in the 3100 to 10400 angstroms range. We have measured the
intensities of a large number of permitted and forbidden emission lines in four
zones of the central part of the galaxy. In particular, we detect faint C II
and O II recombination lines (RLs). This is the first time that these lines are
unambiguously detected in a dwarf starburst galaxy. The physical conditions of
the ionized gas have been derived using a large number of different line
intensity ratios. Chemical abundances of He, N, O, Ne, S, Cl, Ar, and Fe have
been determined following the standard methods. In addition, C^{++} and O^{++}
abundances have been derived from pure RLs. These abundances are larger than
those obtained from collisionally excited lines, (CELs) (from 0.30 to 0.40 dex
for C^{++} and from 0.19 to 0.28 dex for O^{++}). This result is consistent
with a temperature fluctuations parameter (t2) between 0.050 and 0.072. We
confirm previous results that indicate the presence of a localized N enrichment
in certain zones of the center of the galaxy. Moreover, our results also
indicate a possible slight He overabundance in the same zones. The enrichment
pattern agrees with that expected for the pollution by the ejecta of massive
stars in the Wolf-Rayet (WR) phase. The amount of enriched material needed to
produce the observed overabundance is consistent with the mass lost by the
number of WR stars estimated in the starbursts. Finally, we discuss the
possible origin of the difference between abundances derived from RLs and CELs
in H II regions, finding that a recent hypothesis based on the delayed
enrichment by SNe ejecta inclusions seems not to explain the observed features.
NGC~5253. The data have been taken with the Very Large Telescope UVES echelle
spectrograph in the 3100 to 10400 angstroms range. We have measured the
intensities of a large number of permitted and forbidden emission lines in four
zones of the central part of the galaxy. In particular, we detect faint C II
and O II recombination lines (RLs). This is the first time that these lines are
unambiguously detected in a dwarf starburst galaxy. The physical conditions of
the ionized gas have been derived using a large number of different line
intensity ratios. Chemical abundances of He, N, O, Ne, S, Cl, Ar, and Fe have
been determined following the standard methods. In addition, C^{++} and O^{++}
abundances have been derived from pure RLs. These abundances are larger than
those obtained from collisionally excited lines, (CELs) (from 0.30 to 0.40 dex
for C^{++} and from 0.19 to 0.28 dex for O^{++}). This result is consistent
with a temperature fluctuations parameter (t2) between 0.050 and 0.072. We
confirm previous results that indicate the presence of a localized N enrichment
in certain zones of the center of the galaxy. Moreover, our results also
indicate a possible slight He overabundance in the same zones. The enrichment
pattern agrees with that expected for the pollution by the ejecta of massive
stars in the Wolf-Rayet (WR) phase. The amount of enriched material needed to
produce the observed overabundance is consistent with the mass lost by the
number of WR stars estimated in the starbursts. Finally, we discuss the
possible origin of the difference between abundances derived from RLs and CELs
in H II regions, finding that a recent hypothesis based on the delayed
enrichment by SNe ejecta inclusions seems not to explain the observed features.