The M33 Metallicity Project: Resolving the Abundance Gradient Discrepancies in M33

Abstract

We present a new determination of the metallicity gradient in M33, based on Keck/LRIS measurements of oxygen abundances using the temperature-sensitive emission line [OIII] 4363 A in 61 HII regions. These data approximately triple the sample of direct oxygen abundances in M33. We find a central abundance of 12 + log(O/H) = 8.36+/-0.04 and a slope of -0.027+/-0.012 dex/kpc, in agreement with infrared measurements of the neon abundance gradient but much shallower than most previous oxygen gradient measurements. There is substantial intrinsic scatter of 0.11 dex in the metallicity at any given radius in M33, which imposes a fundamental limit on the accuracy of gradient measurements that rely on small samples of objects. We also show that the ionization state of neon does not follow the ionization state of oxygen as is commonly assumed, suggesting that neon abundance measurements from optical emission lines require careful treatment of the ionization corrections.

10 pages, Accepted to ApJ

References in corpus (2)

• The metallicity gradient of M 33: chemical abundances of HII regions
• Neon and Argon optical emission lines in ionized gaseous nebulae: Implications and applications

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• Star formation in M33: multiwavelength signatures across the disk
• The cluster birthline in M33
• A photodissociation model for the morphology of the HI near OB associations in M33
• Massive stars in the nuclei and arms of spirals
• A Metallicity Map of M33