The Circumgalactic Environment of Bright IRAS Galaxies

This paper systematically studies, for the first time, the circumgalactic environment of bright IRAS galaxies as defined in 1989 by Soifer and coworkers. While the role of gravitational interaction for luminous and ultraluminous IRAS galaxies has been well established by various studies, the situation is by far more obscure in the IR luminosity range of the bright IRAS sample, 1010 L☉ ≲ LFIR ≲ 1011 L☉. To easily identify nearby companion galaxies, the bright IRAS sample is restricted to 87 objects with redshift range 0.008 ≤ z ≤ 0.018 and Galactic latitude δ ≥ . A control sample, selected from the CfA redshift-survey catalog, includes 90 objects matching the IRAS bright galaxy survey sample for distribution of isophotal diameter, redshift, and morphological type. From a search of nearby companion galaxies within 250 kpc in the second-generation Digitized Sky Survey (DSS-II), we find that the circumgalactic environments of bright IRAS galaxies contain more large companions than the galaxies in the optically selected control sample and are similar to those of Seyfert 2 galaxies. We find a weak correlation over a wide range of far-IR luminosity (109 L☉ ≲ LFIR ≲ 1012.5 L☉) between projected separation and LFIR, which confirms a very close relationship between the star formation rate of a galaxy and the strength of gravitational perturbations. We also find that the far-IR colors depend on whether a source is isolated or interacting. Finally, we discuss the intrinsic difference between and evolution expectations for the bright IRAS galaxies and the control sample, as well as the relationship between starbursting and active galaxies.