Galaxies: stellar content

Pagel, B.E.J. 1992a, in D. Alloin G. Stasinska (eds.), The Feedback of Chemical Evolution on the Stellar Content of Galaxies, Paris Observatoire, p. 87. 

APPLICATION OP NEAR-IR SPECTROSCOPY TO THE STUDY OF THE STELLAR CONTENT IN STARBURST GALAXIES... 

Key words Near-IR Spectroscopy - Stellar Content of Galaxies... 

NGC 3603 is a young (2—3 Myr, Melnick et al. 1989, MTT) cluster whose numerous OB and two WN stars ionize the largest KQ region in the Galaxy. This duster is very rich and dense, and while this complicates the data analysis, it also makes contamination by iidd stars a less serious problem. I present here the first results of a systematic infrared study of the stellar content of this duster. 

The abundance patterns of individual stars of different ages and environments enable us to unlock the evolutionary history of galaxies. Many physical characteristics of a galaxy may change over time, such as shape and colour, however the metal content and abundance ratios of stellar atmospheres are not so easy to tamper with. Stars retain the chemical imprint of the interstellar gas out of which they formed, and metals can only increase with time. This method to study galaxy evolution has been elegantly named Chemical Tagging [2],... 

In Fig. 1 we display the log(N/0) vs. time and log(N/0) vs. log(0/H)+12 behaviours predicted by two successful models for NGC 1569 and NGC 1705. These models well reproduce several observational constraints - the present-day gaseous and total masses as well as the overall metallicity and oxygen content of the gas - by adopting the same prescriptions on the stellar nucleosynthesis, stellar IMF and galactic outflow onset conditions and efficiency. However, as can be seen from Fig. 1, the present-day N/O ratio is reproduced only for NGC 1569, whilst for NGC 1705 the theoretical N/O ratio during the last 4 Gyr of galaxy s evolution is 0.3-0.4 dex higher than observed at the present time. 

The metallicity in elliptical galaxies always refers to the metal content of the stars, in particular of the stellar population dominating in the visual light. For this reason we should define the average stellar metallicity. In particular, the average metallicity of a composite stellar population averaged on the mass is ... 

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