Extragalactic archeology with the GHOSTS Survey

I. Age-resolved disk structure of nearby low-mass galaxies

¹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
e-mail: dstreich@aip.de
² Department of Physics & Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487, USA
³ Department of Astronomy, University of Michigan, 304 West Hall, 1085 S. University Ave., Ann Arbor, MI 48109, USA
⁴ University of Leiden, Sterrenwacht Leiden, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
⁵ Max Planck Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
⁶ Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195, USA

Received: 3 March 2015
Accepted: 29 August 2015

Abstract

Aims. We study the individual evolution histories of three nearby low-mass edge-on galaxies (IC 5052, NGC 4244, and NGC 5023).

Methods. Using resolved stellar populations, we constructed star count density maps for populations of different ages and analyzed the change of structural parameters with stellar age within each galaxy.

Results. We do not detect a separate thick disk in any of the three galaxies, even though our observations cover a wider range in equivalent surface brightness than any integrated light study. While scale heights increase with age, each population can be well described by a single disk. Two of the galaxies contain a very weak additional component, which we identify as the faint halo. The mass of these faint halos is lower than 1% of the mass of the disk. The three galaxies show low vertical heating rates, which are much lower than the heating rate of the Milky Way. This indicates that heating agents, such as giant molecular clouds and spiral structure, are weak in low-mass galaxies. All populations in the three galaxies exhibit no or only little flaring. While this finding is consistent with previous integrated light studies, it poses strong constraints on galaxy simulations, where strong flaring is often found as a result of interactions or radial migration.