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Astron. Astrophys. 345, 733-746 (1999)


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The abundance of nitrogen in starburst nucleus galaxies *

R. Coziol **  1, R.E. CarlosReyes 2,3, S. Considère 4, E. Davoust 5 and T. Contini 6

1 Observatório Nacional, Rua Gal. José Cristino, 77-20921-400, Rio de Janeiro, RJ., Brazil
2 Laboratório Nacional de Astrofísica - LNA/CNPq, CP 21, 37500-000 Itajubá, MG, Brazil
3 Seminario Permanente de Astronomía y Ciencias Espaciales, FCF, UNMSM, Líma, Perú
4 UPRES-A CNRS 6091, Observatoire de Besançon, B.P. 1615, F-25010 Besançon cedex, France
5 UMR 5572, Observatoire Midi-Pyrénées, 14 avenue E. Belin, F-31400 Toulouse, France
6 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München, Germany

Received 7 January 1999 / Accepted 12 March 1999

Abstract

We show that the excess of nitrogen emission observed in a large sample of Starburst Nucleus Galaxies (SBNGs) can only be explained at a given metallicity by an overabundance of nitrogen with respect to normal H II regions in the disks of late-type spirals. The N/O ratios in the SBNGs are comparable to the values found in the bulges of normal early-type spirals, which suggests that what we observe could be the main production of nitrogen in the bulges of these galaxies.

The variation of the N/O ratio as a function of metallicity in SBNGs follows a [FORMULA] relation, but the increase of nitrogen does not appear as a continuous process. In SBNGs, nitrogen is probably produced by different populations of intermediate-mass stars, which were formed during past sequences of bursts of star formation. This assumption pushes the origin of the main bursts 2-3 Gyrs back in the past. On a cosmological scale, this time interval corresponds to redshifts [FORMULA], where a significant increase of star formation activity occurred. The origin of the SBNG phenomenon would thus have cosmological implications, it would be related to a more active phase of star formation in the Universe sometime in its recent past.

Key words: galaxies: starburst – galaxies: abundances – galaxies: evolution

* Based on observations obtained at the 193cm telescope of Observatoire de Haute-Provence, operated by INSU (CNRS)
** PRONEX/FINEP - P. 246 - 41.96.0908.00

Send offprint requests to: E. Davoust (davoust@obs-mip.fr)

© European Southern Observatory (ESO) 1999

Online publication: April 28, 1999

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