The Effect of Minor and Major Mergers on the Evolution of Low Excitation Radio Galaxies

Abstract

We use deep, ${\mu }_r\lesssim 28\text{mag}{\text{arcsec}}^{-2}$, $r$-band imaging from the Dark Energy Camera Legacy Survey (DECaLS) to search for past, or ongoing, merger activity in a sample of $282$ Low Excitation Radio Galaxies (LERGs) at $z<0.07$. Our principle aim is to assess the the role of mergers in the evolution of LERGs. Exploiting the imaging depth, we classify tidal remnants around galaxies as both minor and major morphological disturbances for our LERG sample and $1,622$ control galaxies matched in redshift, stellar mass, and environment. In groups and in the field, the LERG minor merger fraction is consistent with the control population. In galaxy clusters, $8.8\pm 2.9$ % of LERGs show evidence of recent minor mergers in contrast to $23.0\pm 2.0$ % of controls. This $\sim 4\sigma$ deficit of minor mergers in cluster LERGs suggests these events may inhibit this type of nuclear activity for galaxies within the cluster environment. We observe a $>4\sigma$ excess of major mergers in the LERGs with $M_{\ast }\lesssim 10^{11}{\text{M}}_{\odot }$, with $10\pm 1.5$ % of these AGN involved in such large-scale interactions compared to $3.2\pm 0.4$% of control galaxies. This excess of major mergers in LERGs decreases with increasing stellar mass, vanishing by $M_{\ast }>10^{11.3}{\text{M}}_{\odot }$. These observations show that minor mergers do not fuel LERGs, and are consistent with typical LERGs being powered by accretion of matter from their halo. Where LERGs are associated with major mergers, these objects may evolve into more efficiently accreting active galactic nuclei as the merger progresses and more gas falls on to the central engine.

18 pages, 7 figures, 2 tables, accepted for publication in ApJ

References in corpus (26)

• Galaxy Groups in the SDSS DR4: I. The Catalogue and Basic Properties
• Galaxy Merger Morphologies and Time-Scales from Simulations of Equal-Mass Gas-Rich Disc Mergers
• Hot and cold gas accretion and feedback in radio-loud active galaxies
• The Atlas3D project -- XXIX. The new look of early-type galaxies and surrounding fields disclosed by extremely deep optical images
• On the prevalence of radio-loud AGN in brightest cluster galaxies: implications for AGN heating of cooling flows
• An Infrared Survey of Brightest Cluster Galaxies. II: Why are Some Brightest Cluster Galaxies Forming Stars?
• Raining on black holes and massive galaxies: the top-down multiphase condensation model
• The X-ray nuclei of intermediate-redshift radio sources
• Ram pressure feeding super-massive black holes
• On the Bardeen-Petterson Effect in black hole accretion discs
• The Luminosity Dependence of the Galaxy Merger Rate
• Host galaxies of luminous z$\sim$0.6 quasars: Major mergers are not prevalent at the highest AGN luminosities
• Radio Jets in Galaxies with Actively Accreting Black Holes: new insights from the SDSS
• Incidence of WISE-Selected Obscured AGNs in Major Mergers and Interactions from the SDSS
• On the lifetime of merger features of equal-mass disk mergers
• Galaxy And Mass Assembly: The 1.4GHz SFR indicator, SFR-M* relation and predictions for ASKAP-GAMA
• Galaxy pairs in the Sloan Digital Sky Survey - XII: The fuelling mechanism of low excitation radio-loud AGN
• Evidence for recent star formation in BCGs: a correspondence between blue cores and UV excess
• Galaxy And Mass Assembly (GAMA): Active Galactic Nuclei in Pairs of Galaxies
• A Spectro-photometric Search for Galaxy Clusters in SDSS
• The internal dynamics of the Local Group dwarf elliptical galaxies NGC147, NGC185, and NGC205
• Delayed triggering of radio Active Galactic Nuclei in gas-rich minor mergers in the local Universe
• Galaxy And Mass Assembly (GAMA): The environments of high- and low- excitation radio galaxies
• Galaxy And Mass Assembly (GAMA): The effect of galaxy group environment on active galactic nuclei
• An Active Galactic Nucleus Caught in the Act of Turning Off and On
• The Role of Host Galaxy for the Environmental Dependence of Active Nuclei in Local Galaxies