H. Bravo-Alfaro,1 R. Coziol,1 and E. Brinks2
1 Depto. de Astronomía, Universidad de Guanajuato, Apdo. Postal 144, 36000 Guanajuato, Gto., México (hector@astro.ugto.mx, rcoziol@astro.ugto.mx).
2 Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, U.K. (ebrinks@star.herts.ac.uk).
Received 2005 August 17
Accepted 2006 June 14
RESUMEN
Presentamos imágenes J y H de Haro 2, las cuales confirman que el índice J-H es típico de una galaxia S0 ligeramente azul. La ausencia de asimetrías en el NIR de la zona central es similar a lo observado en galaxias tempranas a pesar de ser una galaxia rica en gas (tanto H I como CO) y de tener una elevada tasa de formación estelar. Con el fin de entender mejor esta peculiar galaxia, obtuvimos espectros ópticos de mediana resolución, los cuales sugieren formación estelar continua durante más de 108 años. Esta edad para el brote es consistente con la abundancia de oxígeno y con el cociente nitrógeno a oxígeno. Reanalizamos datos H i del VLA, que comparados con el NIR y con mapas de CO (1-0) confirman un evento de importante acreción de gas, probablemente mediante una interacción con una galaxia rica en gas. Nuestras observaciones indican que Haro 2 es una enana elíptica que sufrió una interacción indirecta hace más de 108 años, lo que produjo la creación de una gran cantidad de gas y el subsecuente brote de formación estelar.
ABSTRACT
We carried out near infrared (NIR) imaging of the BCD Haro 2 in J and H bands which confirms that the J-H color is typical of a slightly blue S0 galaxy. The absence of asymmetries in the central NIR light distribution is similar to what is seen in unperturbed early-type galaxies, in spite of being a gas rich galaxy (in both H I and CO), with a high SFR. To better understand this peculiar object we obtained medium-resolution optical spectroscopy, which suggests continuous star formation over the past few ×108 yr. This age for the burst is consistent with the observed oxygen abundance and with the nitrogen to oxygen ratio. We reanalyze VLA H I data which, compared with the NIR images and CO(1-0) maps, confirm a major gas accretion event, most likely the result of an interaction with a gas rich companion. Our observations indicate that Haro 2 is likely a dwarf elliptical which suffered a fly-by interaction a few times 108 years ago; this resulted in the accretion of a substantial amount of gas and the subsequent triggering of star formation.
Key Words: GALAXIES: DWARF - GALAXIES: INDIVIDUAL (HARO 2) - GALAXIES: KINEMATICS AND DYNAMICS - TECHNIQUES: SPECTROSCOPIC.
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]]> Acknowledgements
We thank an anonymous referee for comments which significantly improved this article. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated for NASA by the Jet Propulsion Laboratory, California Institute of Technology. We have also used the Digital Sky Survey, produced at the Space Telescope Science Institute. HBA and RC thank CONACyT, México, for its support through grant 40194-F.
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