Environments of dwarf galaxies with optical AGN characteristics

Mikkel T Kristensen,Samantha Penny,Kevin Pimbblet

doi:10.1093/mnras/staa1719

Mikkel T Kristensen, Samantha Penny + Show 1 more

Open Access

https://doi.org/10.1093/mnras/staa1719

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Abstract

ABSTRACT This study aims to explore the relation between dwarf galaxies (M* ≤ 5 × 109 M⊙) with active galactic nuclei (AGNs) and their environment by comparing neighbourhood parameters of AGN and non-AGN samples. Using the NASA-Sloan Atlas, both the local environment and the immediate environment of dwarf galaxies with z ≤ 0.055 are analysed. Of the 145 155 galaxies in the catalogue, 62 258 of them are classified as dwarf galaxies, and by employing two AGN selection methods based on emission-line fluxes (BPT and WHAN), 4476 are found to have AGN characteristics in their optical spectra. Regardless of selection method, this study finds no discernible differences in environment between AGN and non-AGN host dwarf galaxies and these results indicate that environment is not an important factor in triggering AGN activity in dwarf galaxies. This is in line with existing literature on environments of regular galaxies with AGNs and suggests universality in terms of reaction to environment across the mass regime. The biases of AGN selection in low-mass galaxies, and the biases of different measures of environment are also considered. It is found that there are several mass trends in emission-line ratios and that the SDSS fibre covers galaxies non-uniformly with redshift. These biases should be accounted for in future work by possibly including other wavelength regimes or mass weighting of emission-line ratios. Lastly, a discussion of the environment estimation methods is included since they may not gauge the desired properties due to factors such as time delay or using loosely constrained proxy parameters.

Highlights

Galaxies are dynamical objects that evolve and mature over time
Dense local environments have a detrimental effect on the cold gas reservoirs by stripping and heating it while strong galaxy interactions can enhance AGN activity by perturbing the otherwise stable structures, though neither effects can be inferred from the results of this study
This study finds that the environments of AGN dwarf galaxies are no different than the environments of regular dwarf galaxies regardless of AGN selection method

Summary

Introduction

Galaxies are dynamical objects that evolve and mature over time Internal processes such as star formation, supernovae, and nuclear activity and external ones such as galaxy interactions (Moore et al 1996), ram-pressure stripping (Gunn & Gott 1972), and intergalactic medium accretion can change the composition and structure of galaxies and decide their futures. Many of these processes are strongly correlated with stellar mass or environment (Kauffmann et al 2003; Miller et al 2003; Baldry et al 2006; Peng et al 2010, 2012). Field dwarfs are very much shaped only by internal processes while environmental effects dominate lowmass galaxies in clusters and groups (Haines et al 2007; Peng et al 2010)

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Conclusion