Galaxy Zoo: the environmental dependence of bars and bulges in disc galaxies

Abstract

We present an analysis of the environmental dependence of bars and bulges in disc galaxies, using a volume‐limited catalogue of 15 810 galaxies at z < 0.06 from the Sloan Digital Sky Survey with visual morphologies from the Galaxy Zoo 2 project. We find that the likelihood of having a bar, or bulge, in disc galaxies increases when the galaxies have redder (optical) colours and larger stellar masses, and observe a transition in the bar and bulge likelihoods at M*= 2 × 1010 M⊙, such that massive disc galaxies are more likely to host bars and bulges. In addition, while some barred and most bulge‐dominated galaxies are on the ‘red sequence’ of the colour–magnitude diagram, we see a wider variety of colours for galaxies that host bars. We use galaxy clustering methods to demonstrate statistically significant environmental correlations of barred, and bulge‐dominated, galaxies, from projected separations of 150 kpc h−1 to 3 Mpc h−1. These environmental correlations appear to be independent of each other: i.e. bulge‐dominated disc galaxies exhibit a significant bar–environment correlation, and barred disc galaxies show a bulge–environment correlation. As a result of sparse sampling tests – our sample is nearly 20 times larger than those used previously – we argue that previous studies that did not detect a bar–environment correlation were likely inhibited by small number statistics. We demonstrate that approximately half of the bar–environment correlation can be explained by the fact that more massive dark matter haloes host redder disc galaxies, which are then more likely to have bars; this fraction is estimated to be 50 ± 10 per cent from a mock catalogue analysis and 60 ± 5 per cent from the data. Likewise, we show that the environmental dependence of stellar mass can only explain a smaller fraction (25 ± 10 per cent) of the bar–environment correlation. Therefore, a significant fraction of our observed environmental dependence of barred galaxies is not due to colour or stellar mass dependences, and hence must be due to another galaxy property, such as gas content, or to environmental influences. Finally, by analysing the projected clustering of barred and unbarred disc galaxies with halo occupation models, we argue that barred galaxies are in slightly higher mass haloes than unbarred ones, and some of them (approximately 25 per cent) are satellite galaxies in groups. We discuss the implications of our results on the effects of minor mergers and interactions on bar formation in disc galaxies.

Simulating the evolution of disc galaxies in a group environment – II. The influence of close encounters between galaxies

“…As shown in tal dependence between bars/bulges likelihood with environment (e.g. Skibba et al 2012) would appear to be linked to the presence of gaseous components in group galaxies.…”

MUSE tells the story of NGC 4371: The dawning of secular evolution

“…A number of studies have been dedicated to understanding the effects of the environment on bar formation (e.g. Aguerri et al 2009;Li et al 2009;Barazza et al 2009;Méndez-Abreu et al 2010Skibba et al 2012;Lin et al 2014). While it is reasonable to consider the possibility that the bar in NGC 4371 is the result of an interaction, since the galaxy is in a dense environment, this is a difficult claim to defend.…”

The Environment of Barred Galaxies in the Low-Redshift Universe

“…More recently, Skibba et al (2012), also using clustering statistics, reported a positive correlation for bulge-dominated and barred galaxies to be found in denser environments on scales of 150 kpc to a few megaparsecs than their unbarred and diskdominated counterparts and argued that barred galaxies are often central galaxies in low-mass dark matter halos or satellites in more massive ones. Lee et al (2012a) also investigated the dependence of the barred galaxy fraction on environment, finding that once mass and color are fixed, the bar fraction is independent of the background density, but an influence of the nearest neighbor appears when the separation to the nearest neighbor is less than 0.1 times the virial radius of the neighbor.…”