Galaxy Zoo: bars in disc galaxies★

Abstract

We present first results from Galaxy Zoo 2, the second phase of the highly successful Galaxy Zoo project (www.galaxyzoo.org). Using a volume-limited sample of 13 665 disc galaxies (0.01 < z < 0.06 and M r < −19.38), we study the fraction of galaxies with bars as a function of global galaxy properties like colour, luminosity and bulge prominence. Overall, 29.4± 0.5 per cent of galaxies in our sample have a bar, in excellent agreement with previous visually classified samples of galaxies (although this overall fraction is lower than that measured by automated bar-finding methods). We see a clear increase in the bar fraction with redder (g − r) colours, decreased luminosity and in galaxies with more prominent bulges, to the extent that over half of the red, bulge-dominated disc galaxies in our sample possess a bar. We see evidence for a colour bimodality for our sample of disc galaxies, with a 'red sequence' that is both bulge and bar dominated, and a 'blue cloud' which has little, or no, evidence for a (classical) bulge or bar. These results are consistent with similar trends for barred galaxies seen recently both locally and at higher redshift, and with early studies using the RC3. We discuss these results in the context of internal (secular) galaxy evolution scenarios and the possible links to the formation of bars and bulges in disc galaxies.

Rotation-invariant convolutional neural networks for galaxy morphology prediction

“…Data from the Galaxy Zoo projects have already been used in a wide variety of studies on galaxy structure, formation, and evolution (Skibba et al 2009;Bamford et al 2009;Schawinski et al 2009;Darg et al 2010;Masters et al 2010Masters et al , 2011Simmons et al 2013;Melvin et al 2014;Willett et al 2015). Comparisons of Galaxy Zoo morphologies to smaller samples from both experts and automated classifications show high levels of agreement, testifying to the accuracy of the crowdsourced annotations .…”

“…Galaxy Zoo is an online crowdsourcing project where users are asked to describe the morphology of galaxies based on colour images (Lintott et al 2008(Lintott et al , 2011. Our model and analysis uses data from the Galaxy Zoo 2 iteration of the project, which uses colour images from the SDSS and a more detailed classification scheme than the original project .…”

The mass dependence of star formation histories in barred spiral galaxies

“…Their presence is quite ubiquitous, with recent observational data consistently establishing a bar fraction somewhere between 30% and 60% in the local universe (Knapen et al 2000;Martnez & Muriel 2011;Masters et al 2011;Lee et al 2012) and a slightly lesser value at higher redshift (Elmegreen et al 2004;Sheth et al 2008;Simmons et al 2014). Bars create a strong torque on the galaxy (Lynden-Bell 1979; leading to a redistribution of the gaseous and stellar component (Gadotti & dos Anjos 2001;Grand et al 2015) and a transport of angular momentum from the inner to the outer regions of the galaxy ( Seidel et al 2015).…”

On the morphology of dust lanes in galactic bars

“…Roughly 30-40% of the spiral galaxies have a pronounced bar in optical wavelengths and if we take into account weaker bars, the fraction rises up to 60% (de Vaucouleurs 1963;Sellwood & Wilkinson 1993;Marinova & Jogee 2007;Barazza, Jogee & Marinova 2008;Sheth et al 2008;Aguerri, Méndez-Abreu & Corsini 2009;Nair & Abraham 2010;Masters et al 2011). Kinematic data shows the presence of strong non-circular gas motions in bars (e.g.…”