Study DDO 68: new evidences for galaxy youth

TL;DR

This study investigates DDO 68, a very metal-poor galaxy, providing evidence that it is a young galaxy formed recently through a merger, based on stellar population ages and morphology analysis.

Contribution

It offers new insights into DDO 68's stellar populations and supports the hypothesis of its recent formation as a young galaxy through merger events.

Findings

Stellar populations suggest ages from 0.05 to 1 Gyr.

Total visible stellar mass is approximately 2.4x10^7 solar masses.

DDO 68 likely formed recently in a merger about 1 Gyr ago.

Abstract

DDO 68 is the second most metal-poor star-forming galaxy (12+log(O/H)=7.14). Its peculiar optical morphology and the data on its HI distribution and kinematics indicate the merger origin. We use the photometry of the SDSS u,g,r,i images of DDO 68 to estimate its stellar population ages. The available H-alpha-images of DDO 68 were used to select several representative regions without nebular emission. The analysis of obtained colours was performed via comparison with the PEGASE2 evolutionary tracks for various star formation (SF) laws, including the two extremes: instantaneous SF and continuous SF with constant SF rate. The (u-g), (g-r) colours derived for all selected regions, are consistent with a few `instantaneous' SF episodes with ages from ~0.05 to ~1Gyr. Combining the fluxes and colours of visible stellar subsystems with PEGASE2 models, we have estimated the total mass of visible stars in DDO 68 of ~2.4x10^7 Mo. This comprises only ~6% of the total galaxy baryonic mass. All available data do not contradict to the option that DDO 68 is a kind of very rare candidate `young' galaxy, whose dominant stellar build-up took place in course of the recent (with the first encounter ~1 Gyr ago) merger of two very gas-rich disks. DDO 68 best approximates on its properties cosmologically young low-mass galaxies.