Luminosity-metallicity relation for dIrr galaxies in the near-infrared*
European Southern Observatory, Alonso de Cordova, 3107 Santiago, Chile e-mail: [isaviane;vivanov]@eso.org
2 OAPD, vicolo Osservatorio 5, 35122 Padova, Italy e-mail: firstname.lastname@example.org
3 AIM, CEA/DSM/IRFU-Université Paris 7, Service d'Astrophysique, CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France e-mail: email@example.com
4 Department of Physics and Astronomy, 430 Portola Plaza, UCLA, Los Angeles, CA 90095-1547, USA e-mail: firstname.lastname@example.org
5 Institute for Astronomy, University of Hawaii at Manoa, 2680 Woodlawn Drive, Honolulu, HI 96822, USA e-mail: email@example.com
6 Joint Astronomy Centre, 660 N. Aohoku Place, University Park, Hilo, HI 96720, USA e-mail: firstname.lastname@example.org
Accepted: 22 May 2008
Context. The luminosity-metallicity relation is one of the fundamental constraints in the study of galaxy evolution; yet none of the relations available today has been universally accepted by the community.
Aims. The present work is a first step to collect homogeneous abundances and near-infrared (NIR) luminosities for a sample of dwarf irregular (dIrr) galaxies, located in nearby groups. The use of NIR luminosities is intended to provide a better proxy to mass than the blue luminosities commonly used in the literature; in addition, selecting group members reduces the impact of uncertain distances. Accurate abundances are derived to assess the galaxy metallicity.
Methods. Optical spectra are collected for regions in the dIrrs, allowing the determination of oxygen abundances by means of the temperature-sensitive method. For each dIrr galaxy H-band imaging is performed and the total magnitudes are measured via surface photometry.
Results. This high-quality database allows us to build a well-defined luminosity-metallicity relation in the range . The scatter around its linear fit is reduced to 0.11 dex, the lowest of all relations currently available. There might exist a difference between the relation for dIrrs and the relation for giant galaxies, although a firm conclusion should await direct abundance determinations for a significant sample of massive galaxies.
Conclusions. This new dataset provides an improved luminosity-metallicity relation, based on a standard NIR band, for dwarf star-forming galaxies. The relation can now be compared with some confidence to the predictions of models of galaxy evolution. Exciting follow-ups of this work are (a) exploring groups with higher densities, (b) exploring nearby galaxy clusters to probe environmental effects on the luminosity-metallicity relation, and (c) deriving direct oxygen abundances in the central regions of star-forming giant galaxies, to settle the question of a possible dichotomy between the chemical evolution of dwarfs and that of massive galaxies.
Key words: galaxies: fundamental parameters / infrared: galaxies / galaxies: dwarf / galaxies: irregular / galaxies: ISM
Based on data collected at the European Southern Observatory, La Silla, Chile, Proposal N. 70.B-0424(A,B); based on observations made at Lick (UCO) Observatory; based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.
© ESO, 2008