R.D.D. Costa and W.J. Maciel IAG/USP, Brazil

1. Radial abundance gradients in spiral galaxies R.D.D. Costa and W.J. MacielIAG/USP, Brazil The idea Abstract The existence of a radial gradient of abundances in the Milky Way is well known for the solar neighborhood, with the abundances tending to be smaller towards the external edge of the galactic disk. Similar gradients should exist for external galaxies, and their derivation is important to constraint chemical evolution models of spiral galaxies. We propose to perform a systematic survey of chemical abundances of planetary nebulae in nearby galaxies. These data will allow the investigation of the existence of abundance gradients in their disks, the study of the gradient behavior at different galactocentric distances, the effect of bars, and also the time evolution of this gradient. • Gradients in spiral galaxies are expected from galactic evolution models like those by Chiappini et al. 1997 (ApJ 477, 765), Samland et al. 1997 (ApJ 476, 544), Allen et al. 1998 (ApJ 494, 247) or Hou et al. 2000 (A&A 362, 921). • Observational results indicate the existence of this effect, as pointed out, for example, by Kennicutt & Garnett 1996 (ApJ 456, 504), Ferguson et al. 1998 (AJ 116, 673), Henry and Worthey 1999 (PASP 111, 919), generally based on HII regions data and concerning the ratios O/H, N/H and S/H. However, observational constraints have limited the derivation of abundances of extragalactic PNe, and consequently the derivation of gradients, to a few galaxies only. • Making use of multi-objects spectrographs, it is now possible to considerably extend the database of external galaxies for which spectra of individual PNe can be obtained. It is now possible to secure spectra of hundreds of objects simultaneously, allowing the measurement of all PNe in a galaxy in a single exposure, and mantaining therefore the homogeneity of the whole PNe sample in a given galaxy with respect to all observational constraints and parameters. Results for the Milky Way A first test: the radial gradient in M51 and M96 with Gemini/GMOS The radial gradient in the Milky Way: filled circles from Maciel & Quireza 1999 (A&A 345, 629) show the gradient in the inner disk and solar neighborhood. Open circles from Costa et al. 2003 (A&A, submitted) indicate the flattening of the gradient for R > 11 kpc, as predicted from evolutionary models for the galactic disk The time evolution of the radial gradient: when comparing older planetary nebulae (in green) with younger objects (in red and blue), the gradient decreases. Results indicate a decreasing from -0.11 dex/kpc to -0.06 dex/kpc during the last 9 Gyrs, or from -0.08 to -0.06 dex/kpc in the last 5 Gyrs. See details in Maciel et al. 2003 (A&A 397, 667) The field of M96 field (in blue) with the planetary nebulae (in yellow) from Feldmeyer et al. 1999 (ApJ 479, 231) The output from Gemini/GMOS in the multislit mode for 38 planetary nebulae in the field of M51, as displayed by iraf/gemini/gdisplay. Preliminary results are still under analysis. Project supported by IAG/USP, FAPESP and CNPq