The incidence of nuclear activity in galaxy pairs with different morphologies (E+E), (E+S) and (S+S)

We analysed 385 Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) galactic spectra that belong to the catalogue of isolated pairs of galaxies by Karachentsev. The spectra correspond to physical pairs of galaxies defined by a difference in velocity ≤1200 km s−1 and a pair separation ≤100 kpc. We stu...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2016-06, Vol.459 (1), p.291-309
Main Authors: Hernández-Ibarra, Francisco J., Krongold, Yair, Dultzin, Deborah, del Olmo, Ascensión, Perea, Jaime, González, Jesús, Mendoza-Castrejón, Sandro, Bitsakis, Theodoros
Format: Article
Language:English
Subjects:
Accretion disks
Active galactic nuclei
Active galaxies
Astronomy
Diagnostic systems
Extraction
Galaxies
Incidence
Luminosity
Nuclei
Spectra
Stars & galaxies
Velocity
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Summary:We analysed 385 Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) galactic spectra that belong to the catalogue of isolated pairs of galaxies by Karachentsev. The spectra correspond to physical pairs of galaxies defined by a difference in velocity ≤1200 km s−1 and a pair separation ≤100 kpc. We study the incidence of nuclear activity, both star formation and non-thermal – active galactic nuclei (AGNs). After a careful extraction of the nuclear spectra, we use diagnostic diagrams and find that the incidence of AGNs is 48 per cent in emission line paired galaxies and 40 per cent for the total sample (as compared to ∼43 per cent and 41 per cent, respectively, in a sample of isolated galaxies). These results remain after dissecting the effects of morphological type and galactic stellar mass (with only a small, non significant, enhancement of the AGN fraction in galaxy pairs). These results suggest that weak interactions are not necessary and/or sufficient to trigger low-luminosity AGN. Since the fraction of AGN is predominant in early-type spiral galaxies, we conclude that the role of a bulge, and a large gas reservoir are both essential for the triggering of nuclear activity. The most striking result is that Type 1 nuclei are absent from the AGN sample. This result is in conflict with the Unified Model, and suggests that high accretion rates are essential to form the broad line region in active galaxies.
ISSN:0035-8711
1365-2966
DOI:10.1093/mnras/stw480