318 research outputs found
Extragalactic Planetary Nebulae: tracers of the chemical evolution of nearby galaxies
The study of the chemical composition of Planetary Nebulae in external
galaxies is of paramount importance in the fields of stellar evolution and of
the chemical enrichment history of galaxies. In the last years a number of
spectroscopic studies with 6-8m-class telescopes have been devoted to this
subject improving our knowledge of, among other, the time-evolution of the
radial metallicity gradient in disk galaxies, the chemical evolution of dwarf
galaxies, and the stellar evolution at low metallicity.Comment: 8 pages, 4 figures, Invited Review to IAU Symposium 283, "Planetary
Nebulae: an Eye to the Future", Tenerife, 25-29 July 201
Gas-phase oxygen abundances and radial metallicity gradients in the two nearby spiral galaxies NGC7793 and NGC4945
Gas-phase abundances in HII regions of two spiral galaxies, NGC7793 and
NGC4945, have been studied to determine their radial metallicity gradients. We
used the strong-line method to derive oxygen abundances from spectra acquired
with GMOS-S, the multi-object spectrograph on the 8m- Gemini South telescope.
We found that NGC7793 has a well-defined gas-phase radial oxygen gradient of
-0.321 0.112 dex R (or -0.054 0.019 dex kpc)
in the galactocentric range 0.17R/R 0.82, not
dissimilar from gradients calculated with direct abundance methods in galaxies
of similar mass and morphology. We also determined a shallow radial oxygen
gradient in NGC4945, -0.253 0.149 dex R (or -0.019
0.011 dex kpc) for 0.04R/R 0.51, where the
larger relative uncertainty derives mostly from the larger inclination of this
galaxy. NGC7793 and NGC4945 have been selected for this study because they are
similar, in mass and morphology, to M33 and the Milky Way, respectively. Since
at zeroth order we expect the radial metallicity gradients to depend on mass
and galaxy type, we compared our galaxies in the framework of radial
metallicity models best suited for M33 and the Galaxy. We found a good
agreement between M33 and NGC7793, pointing toward similar evolution for the
two galaxies. We notice instead differences between NGC4945 and the radial
metallicity gradient model that best fits the Milky Way. We found that these
differences are likely related to the presence of an AGN combined with a bar in
the central regions of NGC4945, and to its interacting environment.Comment: ApJ, in pres
The radial metallicity gradient and the history of elemental enrichment in M81 through emission-line probes
We present a new set of weak-line abundances of HII regions in M81, based on
Gemini Multi-Object Spectrograph (GMOS) observations. The aim is to derive
plasma and abundance analysis for a sizable set of emission-line targets to
study the galactic chemical contents in the framework of galactic metallicity
gradients. We used the weak-line abundance approach by deriving electron
density and temperatures for several HII regions in M81. Gradient analysis is
based on oxygen abundances.Together with a set of HII region abundances
determined similarly by us with Multi-Mirror Telescope (MMT) spectra, the new
data yield to a radial oxygen gradient of -0.0880.013 dex kpc,
which is steeper than the metallicity gradient obtained for planetary nebulae
(-0.0440.007 dex kpc). This result could be interpreted as gradient
evolution with time: Models of galactic evolution with inside-out disk
formation associated to pre-enriched gas infall would produce such difference
of gradients, although stellar migration effects would also induce a difference
in the metallicity gradients between the old and young populations. By
comparing the M81 metallicity gradients with those of other spiral galaxies,
all consistently derived from weak-line analysis, we can infer that similar
gradient difference is common among spirals. The metallicity gradient slopes
for HII regions and PNe seem to be steeper in M81 than in other galactic disks,
which is likely due to the fact that M81 belongs to a galaxy group. We also
found that M81 has experienced an average oxygen enrichment of 0.140.08
dex in the spatial domain defined by the observations. Our data are compatible
with a break in the radial oxygen gradient slope around R as inferred by
other authors both in M81 and in other galaxies.Comment: Astronomy and Astrophysics, in pres
Coevolution of metallicity and star formation in galaxies to z=3.7: I. A fundamental plane
With the aim of understanding the coevolution of star formation rate (SFR),
stellar mass (M*), and oxygen abundance (O/H) in galaxies up to redshift z=3.7,
we have compiled the largest available dataset for studying Metallicity
Evolution and Galaxy Assembly (MEGA); it comprises roughly 1000 galaxies with a
common O/H calibration and spans almost two orders of magnitude in metallicity,
a factor of 10^6 in SFR, and a factor of 10^5 in stellar mass. From a Principal
Component Analysis, we find that the 3-dimensional parameter space reduces to a
Fundamental Plane of Metallicity (FPZ) given by 12+log(O/H) = -0.14 log (SFR) +
0.37 log (M*) + 4.82. The mean O/H FPZ residuals are small (0.16 dex) and
consistent with trends found in smaller galaxy samples with more limited ranges
in M*, SFR, and O/H. Importantly, the FPZ is found to be redshift-invariant
within the uncertainties. In a companion paper, these results are interpreted
with an updated version of the model presented by Dayal et al. (2013).Comment: 19 pages, 10 figures, 4 tables, accepted for publication in MNRA
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