Dwarf Galaxies: From the Deep Universe to the Present Proceedings IAU Symposium No. 344, 2019 K. B. W. McQuinn & S. Stierwalt, eds. c  International Astronomical Union 2019 doi:10.1017/S1743921318008098 Mass Distribution in Stellar Structures of Local Dwarfs Kar´ ın Men´ endez-Delmestre 1 , Yasmin Coelho 1 , Marco Grossi 1 and Kartik Sheth 2 1 Valongo Observatory, Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil email: kmd@astro.ufrj.br 2 NASA Headquarters Washington DC, USA Abstract. We study the distribution of mid-infrared light in stellar structures in a large sample (∼ 400) of low-mass (M stellar < 10 9 MSun) galaxies. Our sample is selected from the Spitzer Survey of Stellar Structures in Galaxies (S4G), which entails deep imaging of nearby galaxies with the IRAC instrument at 3.6/4.5 μm. Based on the 2D decomposition of the 3.6μm images, we find that the majority (∼65%) of galaxies in our sample is well-fit by a single disk profile. The rest of the sample is more adequately fit by a disk and an additional component (e.g., bar, nucleus, bulge, second disk component). Bars are present in ∼11% of the sample, marking a sharp drop in the bar fraction compared to that found for more massive galaxies. The typical contribution of bars to the 3.6 μm light in dwarfs is ∼1-2%, lower than that found in more massive galaxies. These results bring a number of issues into question: why do low-mass galaxies have such low bar fraction? does the bar instability act differently in low-mass galaxies such that a smaller proportion of stellar mass is typically involved in the bar structure? Is the fact that dwarfs are more dark matter dominated playing a role? Keywords. galaxies: dwarf, galaxies: structure, infrared: galaxies 1. Introduction Galaxies in the local universe are a fossil record of events in the distant universe and present critical constraints for examining models of formation and evolution of galaxies. Based on the Spitzer Survey of Stellar Structure in Galaxies (S4G; Sheth et al. 2010) database, we have set out to quantify the relative amount of stellar light typically con- tained within different stellar structures (such as bulge, disk, bar) in nearby galaxies, in the interest of establishing a systematic characterization of the stellar mass distribution in these structures. S4G entails deep mid-infrared (mid-IR) imaging of ∼2300 nearby (< 40 Mpc) relatively-large (D 25 > 1’) relatively-bright (m Bcorr < 15.5) galaxies with the Infrared Array Camera (IRAC) onboard Spitzer at 3.6/4.5 μm. With a surface bright- ness limit at 3.6μm of 27 mag/arcsec 2 , this survey is unique in its capability to probe stellar surface densities down to ≪ 1M Sun /pc 2 , which is of particular interest when studying faint extended objects. The choice of mid-IR is particularly important because the emission of low mass stars, that dominate stellar mass in galaxies, dominates the flux in these bands. The S4G collaboration makes the reduced images publicly available (Mu˜ noz-Mateos, J.-C. et al. 2015) via the NASA/IPAC Infrared Science Archive (IRSA). In an interest to focus our study on dwarf galaxies, we select all galaxies from the S4G sample with low stellar masses (M stellar < 10 9 M Sun ). Considering that one of our drivers is to explore the prevalence of bars in such galaxies, we restrict our sample to galaxies with inclinations lower than 65 degrees; bars in more inclined galaxies are notoriously difficult to detect. These cuts resulted in a total of 454 dwarf galaxies. As we 340 https://doi.org/10.1017/S1743921318008098 Published online by Cambridge University Press