Automated bar detection in local disc galaxies from the SDSS - The colors of bars

TL;DR

This study develops an automatic method to identify barred late-type galaxies in SDSS images, revealing that bars are more common in massive galaxies and influence their color profiles, supporting the bar-quenching scenario.

Contribution

An automatic isophotal fitting procedure was created to detect bars in large galaxy samples without visual inspection, enabling statistical analysis of bar properties and their effects.

Findings

36% of face-on late-type galaxies are barred.

Barred galaxies are more common at higher stellar masses.

Bars cause redder color gradients inside the corotation radius.

Abstract

This paper describes an automatic isophotal fitting procedure that succeeds, without the support of any visual inspection of neither the images nor the ellipticity/P.A. radial profiles, at extracting a fairly pure sample of barred LTGs among thousands of optical images from the SDSS. The procedure relies on the methods described in Consolandi et al. (2016) to robustly extract the photometrical properties of a large sample of local SDSS galaxies and is tailored to extract bars on the basis of their well-known peculiarities in their P.A. and ellipticity profiles. It has been run on a sample of 5853 galaxies in the Coma and Local supercluster. The procedure extracted for each galaxy a color, an ellipticity and a position angle radial profile of the ellipses fitted to the isophotes. Examining automatically the profiles of 922 face-on late-type galaxies (B/A >0.7) the procedure found that ~ 36 % are barred. The local bar fraction strongly increases with stellar mass. The sample of barred galaxies is used to construct a set of template radial color profiles in order to test the impact of the barred galaxy population on the average color profiles shown by Consolandi et al. (2016) and to test the bar-quenching scenario proposed in Gavazzi et al. (2015). The radial color profile of barred galaxy shows that bars are on average redder than their surrounding disk producing an outside-in gradient toward red in correspondence of their corotation radius. The distribution of the extension of the deprojected length of the bar suggests that bars have strong impacts on the gradients of averaged color profiles. The dependence of the profiles on the mass is consistent with the bar-quenching scenario, i.e. more massive barred galaxies have redder colors (hence older stellar population and suppressed star formation) inside their corotation radius with respect to their lower mass counterparts.