Galaxy Zoo: secular evolution of barred galaxies from structural decomposition of multiband images

Abstract

We present the results of two-component (disc+bar) and three-component (disc+bar+bulge) multiwavelength 2D photometric decompositions of barred galaxies in five SDSS bands (ugriz ). This sample of ∼3,500 nearby (z < 0.06) galaxies with strong bars selected from the Galaxy Zoo citizen science project is the largest sample of barred galaxies to be studied using photometric decompositions which include a bar component. With detailed structural analysis we obtain physical quantities such as the bar-and bulge-to-total luminosity ratios, effective radii, Sérsic indices and colours of the individual components. We observe a clear difference in the colours of the components, the discs being bluer than the bars and bulges. An overwhelming fraction of bulge components have Sérsic indices consistent with being pseudobulges. By comparing the barred galaxies with a mass-matched and volume-limited sample of unbarred galaxies, we examine the connection between the presence of a large-scale galactic bar and the properties of discs and bulges. We find that the discs of unbarred galaxies are significantly bluer compared to the discs of barred galaxies, while there is no significant difference in the colours of the bulges. We find possible evidence of secular evolution via bars that leads to the build-up of pseudobulges and to the quenching of star formation in the discs. We identify a subsample of unbarred galaxies with an inner lens/oval and find that their properties are similar to barred galaxies, consistent with an evolutionary scenario in which bars dissolve into lenses. This scenario deserves further investigation through both theoretical and observational work.

Structural and photometric properties of barred galaxies from the Auriga cosmological simulations

“…Also, from multicomponent decomposition of S 4 G galaxies (Kim et al 2014, Salo et al 2015, barred galaxies such as NGC 7552, NGC 5728, and NGC 7582 have morphology and bar-to-total ratios comparable to those Auriga galaxies with the most luminous bars. Other morphological decompositions performed by Weinzirl et al (2009) or Kruk et al (2018) reports also several early-type galaxies with Bar/T > 0.3. In Fig.…”

“…Also, future studies on cosmological simulations must pursue statistical significant samples of simulated galaxies with the aim of reproducing the observed statistical properties of bars. a community-developed core Python package for Astronomy (Astropy Collaboration et al 2013;2018); NumPy (van der Walt et al 2011); pandas (McKinney 2010) and PyRAF, a product of the Space Telescope Science Institute, which is operated by AURA for NASA. Plots were generated using Matplotlib (Hunter 2007)…”

Galaxy Zoo: probabilistic morphology through Bayesian CNNs and active learning

“…This matches previous results (and intuition) that 'Smooth or Featured' is an easier question to answer than 'Bar'. Identifying bars, particularly weak bars, is challenging for both humans (Masters et al 2012;Kruk et al 2018) and machines (including CNNs, Domínguez Sánchez et al 2018).…”

Revealing the cosmic evolution of boxy/peanut-shaped bulges from HST COSMOS and SDSS

“…Imaging surveys at optical wavelengths only sample the rest frame optical up to z ∼ 1, while at higher redshifts it probes the rest frame ultraviolet, where the images show very different structures (Conselice et al 2004). This issue is particularly acute for barred galaxies, since bars inhibit star formation and have been shown to have redder colours and thus host an older population of stars than the disc (Kruk et al 2018). Bars are therefore less evident in the rest frame ultraviolet.…”