A 3-Dimensional study of the Local Environment of Bright IRAS Galaxies: The AGN/Starburst connection

Abstract

We present a 3-dimensional study of the local ($\leq 100 h^{-1}$ kpc) and the large scale ($\leq$ 1 $h^{-1}$ Mpc) environment of Bright IRAS Galaxies (BIRGs). For this purpose we use 87 BIRGs located at high galactic latitudes (with 0.008$\leq z \leq$0.018) as well as a control sample of non-active galaxies having the same morphological, redshift and diameter size distributions as the corresponding BIRG sample. Using the Center for Astrophysics (CfA2) and Southern Sky Redshift Survey (SSRS) galaxy catalogues ($m_b\lesssim 15.5$)as well as our own spectroscopic observations ($m_b\lesssim19.0$) 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 Sy1 and Sy2 galaxies of Koulouridis et al. (2006) we find that BIRGs have a similar environment as Sy2s, although the fraction of BIRGs with a bright close neighbor is even higher than that of Sy2 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 non-interacting starbursts and a resemblance between the colors of non-interacting starbursts and Sy2s. Our results support the view where close interactions can drive molecular clouds towards 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) AGN. Finally, the complete disentanglement of the pair gives birth to an unobscured (type 1) AGN.