Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2011-11-17
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
Submitted in ApJ. arXiv admin note: substantial text overlap with arXiv:0910.1355v1 (withdrawn)
Scientific paper
We present a follow-up study on a series of papers concerning the role of close interactions as a possible triggering mechanism of the activity of AGN and starburst galaxies. We have already studied the close (< 100 kpc/h) and the large scale (< 1 Mpc/h) environment of Sy1, Sy2 and Bright IRAS galaxies (BIRG) and their respective control samples. The results led us to the conclusion that a close encounter appears capable of activating a sequence where a normal galaxy becomes first a starburst, then a Sy2 and finally a Sy1. However since both galaxies of an interacting pair should be affected, we present here optical spectroscopy and X-ray imaging of the neighbouring galaxies around our original Seyfert and BIRG galaxy samples. Based on optical spectroscopy we find that more than 70% of all neighbouring galaxies exhibit thermal or/and nuclear activity (namely enhanced star formation, starbursting and/or AGN), while an additional X-ray analysis showed that this percentage can reach up to 100%. Furthermore, we discovered various trends regarding the type and strength of the neighbour's activity with respect to the activity of the central galaxy, the most important of which is that the neighbours of Sy2 galaxies are systematically more ionized than the neighbours of Sy1s, a fact that indicates differences in metallicity, stellar mass and star-formation history between the samples. Our results not only strengthen the link between close galaxy interactions and activity, but also provide more clues regarding the evolutionary sequence inferred by our previous studies.
Chavushyan Vahram
Dultzin Deborah
Georgantopoulos Ioannis
Koulouridis Elias
Krongold Yair
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