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Title: Metallicity inhomogeneities in local star-forming galaxies as a sign of recent metal-poor gas accretion

We measure the oxygen metallicity of the ionized gas along the major axis of seven dwarf star-forming galaxies. Two of them, SDSSJ1647+21 and SDSSJ2238+14, show ≅0.5 dex metallicity decrements in inner regions with enhanced star formation activity. This behavior is similar to the metallicity drop observed in a number of local tadpole galaxies by Sánchez Almeida et al., and was interpreted as showing early stages of assembling in disk galaxies, with the star formation sustained by external metal-poor gas accretion. The agreement with tadpoles has several implications. (1) It proves that galaxies other than the local tadpoles present the same unusual metallicity pattern. (2) Our metallicity inhomogeneities were inferred using the direct method, thus discarding systematic errors usually attributed to other methods. (3) Taken together with the tadpole data, our findings suggest a threshold around one-tenth the solar value for the metallicity drops to show up. Although galaxies with clear metallicity drops are rare, the physical mechanism responsible for them may sustain a significant part of the star formation activity in the local universe. We argue that the star formation dependence of the mass-metallicity relationship, as well as other general properties followed by most local disk galaxies, is naturally interpretedmore » as side effects of pristine gas infall. Alternatives to the metal-poor gas accretion are examined as well.« less
Authors:
; ; ;  [1] ;  [2] ;  [3]
  1. Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife (Spain)
  2. Department of Physics and Astronomy, Vassar College, Poughkeepsie, NY 12604 (United States)
  3. IBM Research Division, T.J. Watson Research Center, Yorktown Heights, NY 10598 (United States)
Publication Date:
OSTI Identifier:
22351347
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 783; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; DWARF STARS; ERRORS; EVOLUTION; GALAXIES; LARVAE; MASS; METALLICITY; METALS; OXYGEN; UNIVERSE