Intergalactic H II regions discovered in SINGG

E.V. Ryan-Weber, G.R. Meurer, K.C. Freeman, M.E. Putman, R.L. Webster, M.J. Drinkwater, H.C. Ferguson, D. Hanish, T.M. Heckman, R.C. Kennicutt, V.A. Kilborn, P.M. Knezek, B.S. Koribalski, Martin Meyer, M.S. Oey, R.C. Smith, Lister Staveley-Smith, M.A. Zwaan

    Research output: Contribution to journalArticlepeer-review

    67 Citations (Scopus)

    Abstract

    A number of very small isolated H II regions have been discovered at projected distances up to 30 kpc from their nearest galaxy. These H II regions appear as tiny emission-line objects in narrowband images obtained by the NOAO Survey for Ionization in Neutral Gas Galaxies (SINGG). We present spectroscopic confirmation of four isolated H II regions in two systems; both systems have tidal H I features. The results are consistent with stars forming in interactive debris as a result of cloud-cloud collisions. The Hα luminosities of the isolated H II regions are equivalent to the ionizing flux of only a few O stars each. They are most likely ionized by stars formed in situ and represent atypical star formation in the low-density environment of the outer parts of galaxies. A small but finite intergalactic star formation rate will enrich and ionize the surrounding medium. In one system, NGC 1533, we calculate a star formation rate of 1.5 × 10-3 Modot yr-1, resulting in a metal enrichment of ~1 × 10-3 solar for the continuous formation of stars. Such systems may have been more common in the past and a similar enrichment level is measured for the "metallicity floor" in damped Lyα absorption systems.
    Original languageEnglish
    Pages (from-to)1431-1440
    JournalThe Astronomical Journal
    Volume127
    Issue number3
    DOIs
    Publication statusPublished - 2004

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