Interaction between the Galaxies IC 2163 and NGC 2207

VLA HI observations of the interacting pair IC 2163/NGC 2207 are presented. The velocity and structural anomalies of IC 2163 agree with predictions of N-body galaxy encounter simulations if IC 2163 recently underwent a strong, prograde, in-plane encounter with NGC 2207. The velocity disturbances in NGC 2207 suggests that the main tidal force on NGC 2207 was perpendicular to the disk of NGC 2207

Spitzer Space Telescope IRAC and MIPS observations of the interacting galaxies Ic 2163 and NGC 2207: clumpy emission

Peer reviewe

CO Observations of the Interacting Galaxy Pair NGC 5394/95

Peer reviewe

Metallicity inhomogeneities in local star-forming galaxies as 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 Sanchez Almeida et al. (2013) and 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, are naturally interpreted as side effects of pristine gas infall. Alternatives to the metal poor gas accretion are examined too.Comment: Accepted for publication in ApJ. 10 pages. 5 Fig