A Study of the Distribution of Star-Forming Regions in Luminous Infrared Galaxies by Means of Hα Imaging Observations

We performed Hα imaging observations of 22 luminous infrared galaxies to investigate how the distribution of star-forming regions in these galaxies is related to galaxy interactions. Based on correlation diagrams between Hα flux and continuum emission for individual galaxies, a sequence for the distribution of star-forming regions was found: very compact (∼ 100 pc) nuclear starbursts with almost no star-forming activity in the outer regions (type 1), dominant nuclear starbursts . 1 kpc in size and a negligible contribution from the outer regions (type 2), nuclear starbursts & 1 kpc in size and a significant contribution from the outer regions (type 3), and extended starbursts with relatively faint nuclei (type 4). These classes of star-forming region were found to be strongly related to global star-forming properties such as star-formation efficiency, farinfrared color, and dust extinction. There was a clear tendency for the objects with more compact distributions of star-forming regions to show a higher star-formation efficiency and hotter far-infrared color. An appreciable fraction of the sample objects were dominated by extended starbursts (type 4), which is unexpected in the standard scenario of interaction-induced starburst galaxies. We also found that the distribution of star-forming regions was weakly but clearly related to galaxy morphology: severely disturbed objects had a more concentrated distribution of star-forming regions. This suggests that the properties of galaxy interactions, such as dynamical phase and orbital Visiting Astronomer, Okayama Astrophysical Observatory of National Astronomical Observatory. Department of Astronomy, Faculty of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan Present address: Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, Kamogatacho, Asakuchi-gun, Okayama 719-0232, Japan; [email protected] Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, Kamogata-cho, Asakuchigun, Okayama 719-0232, Japan Department of Applied Physics, Graduate School of Engineering, Hokkaido University, Kita-ku, Sapporo, Hokkaido 060-8628, Japan Shimonoseki City University, Shimonoseki, Yamaguchi 751-8510, Japan Toyama Science Museum, Toyama, Toyama 934-8084, Japan Nishi-Harima Astronomical Observatory, Sayo-cho, Hyogo 679-5313, Japan Kurashiki Science Center, Kurashiki, Okayama 712-8046, Japan