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
Received 7 January 1999 / Accepted 12 March 1999
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 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 , 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
Send offprint requests to: E. Davoust (email@example.com)
© European Southern Observatory (ESO) 1999
Online publication: April 28, 1999