A Three‐dimensional Study of the Local Environment of BrightIRASGalaxies: The Active Galactic Nucleus–Starburst Connection

Abstract

We present a three-dimensional study of the local (≤100 h-1 kpc) and the large scale (≤1 h-1 Mpc) environment of bright IRAS balaxies (BIRGs). For this purpose we use 87 BIRGs located at high Galactic latitudes (with 0.008 ≤ z ≤ 0.018), as well as a control sample of nonactive galaxies having the same morphological, redshift, and diameter size distributions as the corresponding BIRG sample. Using the Center for Astrophysics and the Southern Sky Redshift Survey galaxy catalogs (mb 15.5), as well as our own spectroscopic observations (mb 19.0), for a subsample of the original BIRG sample, we find that the fraction of BIRGs with a close neighbor is significantly higher than that of their control sample. Comparing with a related analysis of Seyfert 1 and Seyfert 2 galaxies by Koulouridis and coworkers, we find that BIRGs have a similar environment to that of Seyfert 2 galaxies, although the fraction of BIRGs with a bright, close neighbor is even higher than that for Seyfert 2 galaxies. An additional analysis of the relation between FIR colors and the type of activity of each BIRG shows a significant difference between the colors of strongly interacting and noninteracting starbursts and a resemblance between the colors of noninteracting starbursts and Seyfert 2 galaxies. Our results support the view that close interactions can drive molecular clouds toward the galactic center, triggering starburst activity and obscuring the nuclear activity. When the close neighbor moves away, starburst activity is reduced with the simultaneous appearance of an obscured (type 2) active galactic nucleus (AGN). Finally, the complete disentanglement of the pair gives birth to an unobscured (type 1) AGN.