Volume 567, July 2014
|Number of page(s)||13|
|Section||Interstellar and circumstellar matter|
|Published online||17 July 2014|
The radial metallicity gradient and the history of elemental enrichment in M 81 through emission-line probes⋆
National Optical Astronomy Observatory,
2 INAF − Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
3 INAF − Istituto di Radioastronomia & Italian ALMA Regional Center, 40129 Bologna, Italy
4 Universidad Autónoma de Madrid, Departamento de Física Teórica C-XI, 28049 Madrid, Spain
Received: 14 January 2014
Accepted: 19 March 2014
Aims. We present a new set of weak-line abundances of HII regions in M 81, which are 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.
Methods. We used the weak-line abundance approach by deriving electron density and temperatures for several HII regions in M 81. Our gradient analysis is based on oxygen abundances.
Results. Together with a set of HII region abundances determined similarly by us with Multi-Mirror Telescope (MMT) spectra, the new data yield a radial oxygen gradient of −0.088 ± 0.013 dex kpc-1, which is steeper than the metallicity gradient obtained for planetary nebulae (−0.044 ± 0.007 dex kpc-1). 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 a difference in gradients, although stellar migration effects would also induce a difference in the metallicity gradients between the old and young populations.
Conclusions. By comparing the M 81 metallicity gradients with those of other spiral galaxies, which were all consistently derived from weak-line analysis, we can infer that a similar gradient difference is common among spirals. The metallicity gradient slopes for HII regions and PNe seem to be steeper in M 81 than in other galactic disks, which is probably because M 81 belongs to a galaxy group. We also found that M 81 has experienced an average oxygen enrichment of 0.14 ± 0.08 dex in the spatial domain defined by the observations. Our data are compatible with a break in the radial oxygen gradient slope around R25 as inferred by other authors both in M 81 and in other galaxies.
Key words: Galaxy: abundances / galaxies: evolution / galaxies: individual: M 81 / HII regions
Full Tables 3 and 4 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/567/A88
© ESO, 2014
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.