科研之友
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摘要
We present spectroscopic observations of 26 galaxies of type E and S0, based on their blue morphologies, located in voids by the study of Grogin & Geller in 1999. Measurements of redshift, velocity dispersion, and four Lick line indices, Mg(b), Fe5270, Fe5335, and H beta with their errors are given for all of these galaxies, along with H beta, [O III], H alpha, and [N II] emission line strengths for a subset of these objects. These sources are brighter than M* for low-density regions and tend to be bluer than their counterpart early-type objects in high-density regions. Using the models of Thomas et al., developed in 2003, gives metal abundances and ages with a median alpha enhancement, [alpha/Fe] = +0.13, and median metal abundance, [Z/H] = +0.22, values comparable to those found for E and S0 galaxies in clusters, but with a wider spread in [Z/H] toward low values. If the emission line subsample is interpreted as younger, the proportion of young objects is higher than for early types in higher-density regions. There is a significant incidence of sources in the sample with emission lines in their spectra (46% with H beta and [O III] and 69% with H alpha or [N II]) as well as shells and rings in their morphologies (19%). The diagnostic log[N II]/H alpha, log[O III]/H beta diagram places 10 of 12 emission line galaxies in or near the star-forming and liner region and two among the Seyferts. The H alpha fluxes indicate star-formation rates of 0.2-1.0 M(circle dot) yr(-1). The percentage of these early-type void galaxies undergoing star formation appears to be higher compared to their cluster counterparts and the range of ages wider.
- 出版日期2008-7
